97 running very hot [Resolved.....Finally!]

1997 ls 4.3 4x4 4dr

After i have done the intake manifold gasket my blazer seems to be running very hot. It would normaly sit between the bigger dasher on the cold side and the 210 mark. In the middle of that. no matter how im driving , what season always sat there. Only when im travinlg some very steep hills of pittsburg it would jump up to 210, but quickly drop. w/ or w/o a/c on. Now my car is running at 210 avg w/o a/c and if i turn the a/c on it will jump to half way in the between dasher of 210 and the red on the hot side in a matter of secs when im driving normal. and if i contine to drive w/ a/c it steped in the red and my check gauge liek came out, at that point i shut it off and let it cool down and got home. Take in note this is all after the intake manifold job. When i did the job i put in a new tensior, idle pully, rad cap, t-stat and flushed the system w/ new dexcool. I check the dexcool lever every morning, and the rad and overflow are full and nice and orange. When the car gets past 210, it really dawgs down(no power) and i can hear gurgling(Air) in my heat core. But only when its hot. 3 days ago i tossed a fan clutch at it after closly follwing the last guy on here w/overheating problems in hope that was the key...... It wasnt. It did help a lil, It hasnt got in the red yet. But still geting way to hot for my comfert. Im kinda stumped now to what it could be, cloged cat, head gasket water pump. I was going to put another t-sat in. The one time i have had 2 bad ones in a row go in. there cheap and easy to pop in. just getting stumped and its really starting to get under my skin. I feel like there somthign wrong EVERY day w/ it. and when i fix one thing there gonna be somting else thats going wrong. So i dont want to toss any more parts at is if there not gonna do anything :banghead: so any ideas guys, Thanks in advance

note- driving it harder speeds everything up. W/ a/c on and about 3/4 gas till about 70mph it was on the last big dasher before the red zone

The gurgle sound is air that is trapped in the cooling system. You need to "burp" or "bleed" it out. That's what's causing your overheating concern.

I agree with Old Master, burp this thing.

Make sure that you didn't install the T-Stat upside down or anything else that is obvious. (Don't be insulted, it happens to the best of us.) Put your T-Stat in a pot of boiling water to check to see if it is opening. You could also try putting a 180° T-Stat in it instead of the 210°.

If all else fails, you might try getting a Reverse Power flush on the Rad.

none taken. I was preety sure it was a 180 t-stat, And yes haha it is in the right way. Im just gonna toss a new rad cap and t-stat at it and hope for the best. if not then the radiator is coming out.

Also i was talking to some other people they were thinking possible blown head gasket.. My oil is good and the car runs good so i dont think it could be.

And will drving around take the air out of there or is the easiest way the way blazerlt's "how to" in the FAQ the best way?

BLT's "how to"

You did properly dilute the fresh Dex-Cool, 50-50 mix right? You're not running straight Anti-freeze are you?

If the air removal does not solve all , I have had the best luck with buying 3' of both 5/8 and 3/4 heater hose, then using them to first reflush the heater core in both directions using only a hose and holding it to the heater hose so not to blow the core, then reconnecting and all that seems to do it - if you tie the heater hoses you removed from the firewall UP, no dex cool will be lost (or very little).

BLT's "how to"

You did properly dilute the fresh Dex-Cool, 50-50 mix right? You're not running straight Anti-freeze are you?

I ran stright water in the system for about 10-15 min till nothing but water came out of the radiator, then i draind the rad and i got about 3/4 of a gallon of dexcool in. Ive done it that way 3 times before and never had a problem. Im gonna try to flush the core real good and new t-stat and see what happens

Just put in a 195 temp stant t-stat. When i took it out the antifreeze was almost water:banghead: :banghead: wooooops. I guess not enough dexcool. I feel preety stupid i know better then that, But when i checked it at the rad neck it look very orange. Any way i flushed and back flushed the heat core, and did the BLT on getting the air out. Burnt my hand a lil. It was like foaming then BAM just a stream of orange. I guess thats when the t-sat opens and i have no more air,,,,,, i hope. When i was filling it i use stight anitfrezze to hopfully balence out the water. I got about 1/2 gallon of dexcool in. SO ill drive it around and let u guys know what happens

:angryfire nothing. It does the same thing. It idle for like 25 min and was perfect. right inbetween the half way mark on the cold side and 210 I took it out slow and it climbed to a lil under 210. i gave it some gas, it jumped a lil over 210 and didnt come back down when i slowed down. I turned a/c on and it jumped up to the middle of 210 and 260 in about 2 min. I turned a/c off and it stayed there. i have no idea what it is now. When i was driving i didnt hear any of the gurgling so i guess i got the air out. but my temp is still kickin my butt.

I know you said you put a new fan Clutch on it, Are the fan blades installed in the right direction? The fan should be marked with the word "FRONT" on the hub, that side should be toward the radiator. The Shroud is installed correctly?

Sorry, I don't mean to sound so insulting, I really am trying to help you. Do you hear the fan working?

Sounds unlikely, but I'd be suspicious that perhaps the new fan clutch isn't working well. I'm in Philly area which has been having the same weather as you, and it seems that my new fan clutch has been engaged the past few days around 80% of the time after warm up. The loud fan woosh-sound is REALLY noticeable particularly during acceleration after sitting at a red light or stopping for a stop sign. If you're not hearing that sound a lot these past few days, that new clutch might be your problem.

I know you said you put a new fan Clutch on it, Are the fan blades installed in the right direction? The fan should be marked with the word "FRONT" on the hub, that side should be toward the radiator. The Shroud is installed correctly?

Sorry, I don't mean to sound so insulting, I really am trying to help you. Do you hear the fan working?


I understand complety. It is put on the right way. It does kick on for about 30 sec everytime the first time i start it up and drive. The only other time is when it hit the middle mark on the hot side. It did kick in once it went past the half way mark, but as soon as it got on the mark or very slighty past it, it shut off. I live about 30 min north of philly, So were having the same out side temps AJT for the most part. Mine is hardly on. SO possible bad fan clucth. But that wouldnt explain why it never did it before. I never had this problem even in heat, this hot and that was with a bad fan clutch, blown manifold gasket, And brown dexcool. Pending how much money i get for my birthday:grinyes: im gonna let a garage deal with it.

Keep on burping it.

Let it sit overnight and then check the coolant level in the rad when dead cold.

Also, did you replace the rad cap?

I understand complety. It is put on the right way. It does kick on for about 30 sec everytime the first time i start it up and drive. The only other time is when it hit the middle mark on the hot side. It did kick in once it went past the half way mark, but as soon as it got on the mark or very slighty past it, it shut off. I live about 30 min north of philly, So were having the same out side temps AJT for the most part. Mine is hardly on. SO possible bad fan clucth. But that wouldnt explain why it never did it before. I never had this problem even in heat, this hot and that was with a bad fan clutch, blown manifold gasket, And brown dexcool. Pending how much money i get for my birthday:grinyes: im gonna let a garage deal with it.

Don't give up just yet. Do like BlazerLT says, keep burping it. Check it in the morning while it is stone cold, before you start it.

You can also get a radiator Pump from Auto Zone (for free) and check for leaks and pressure drop. This will help to find/eliminate bad gaskets, head or intake.

You also said that the water was almost clear when you pulled the T-Stat. I think what you were saying (without knowing it) is that the water was not mixing with the Anti-freeze, which tells me that your water pump might not be pumping. This would seem to explain why it is o.k. at idle and overheats under a load. Can you tell if the coolant is circulating in the Radiator?

At high speeds, most fan clutches really don't do anything but spin along for the ride, the air passing through the rad at 60 MPH cools the rad.

I'm not seeing the signs of air in the system. Usually if there's air, you can rev the engine and the temp will drop. He has the opposite reaction. Also, you said that mostly water ran out of the engine when you put in the new t-stat, right? I'm leaning towards a bad/clogged waterpump also. BTW, how much RTV did you use on that intake gasket?? It's possible to block coolant flow if excess RTV gets into the coolant ports..

have you checked for cruddy Dexcool blockage inside the hose that goes from your rad-cap to your overflow reservoir?

mine was completely blocked ... used a wire clothes-hangar to scrape the inside clean ...




I understand complety. It is put on the right way. It does kick on for about 30 sec everytime the first time i start it up and drive. The only other time is when it hit the middle mark on the hot side. It did kick in once it went past the half way mark, but as soon as it got on the mark or very slighty past it, it shut off. I live about 30 min north of philly, So were having the same out side temps AJT for the most part. Mine is hardly on. SO possible bad fan clucth. But that wouldnt explain why it never did it before. I never had this problem even in heat, this hot and that was with a bad fan clutch, blown manifold gasket, And brown dexcool. Pending how much money i get for my birthday:grinyes: im gonna let a garage deal with it.

I'm not seeing the signs of air in the system. Usually if there's air, you can rev the engine and the temp will drop. He has the opposite reaction. Also, you said that mostly water ran out of the engine when you put in the new t-stat, right? I'm leaning towards a bad/clogged waterpump also. BTW, how much RTV did you use on that intake gasket?? It's possible to block coolant flow if excess RTV gets into the coolant ports..

Naw, water in the system won't cause what you are seeing with the 4.3L.

A new rad cap is needed and the rad cap needs to be taken off in the morning when cold and the rad level needs to be checked.

I can't stress enough, CHANGE THE RAD CAP.

Well, if he ran the engine with water in the block and dexcool in the radiator before installing the new t-stat it should've mixed, right?

Well, if he ran the engine with water in the block and dexcool in the radiator before installing the new t-stat it should've mixed, right?

Yes, it would have and even with a light mix it shouldn't overheat if the rad cap is keeping the sufficient pressure of 16psi which will suppress any overheating unless it was under stressed conditions.

This problem is air in the cooling system which still has to be burped out and a new rad cap installed.

Put the truck front on ramps so the rad is the highest point in the cooling system and when the engine is cold remove the rad cap and allow the engine to come up to temperature. When the t-stat opens the coolant will rush into the engine and you will have to keep on topping up the coolant until it starts to gush out the rad neck which is when you install the new cap cap on quickly.

Also the overflow tank and the tube joining it to the rad should be cleaned and flushed to get all the gunk out of it.

Often the bottom of the overflow tank will get clogged full of crud which will not allow the rad to recover coolant from the overflow tank when cooling and contracting and will find another weakness like the stock faulty acdelco rad cap to suck in air when it should be recovering coolant.

I went through this with my cooling system recently and found this out.

Just trying to pass on the knowledge.

Right, but I'm not referring to the mix, I'm talking about how the water pump should have mixed all that. He said he flushed with water, then drained/filled the radiator with Dex. This would leave water in the block. When started and warmed up, it should have mixed the water in the block with dex from the rad. He said water ran out of the block when putting the new t-stat in. If it ain't mixin', it ain't pumping OR somethings stopped up. I think he did replace the cap, or said he was(hopefully with the right PSI rating). That and cleaning the overflow is a good idea..

EDIT: Also, I noticed if the proper 50/50 mix isn't used, it can throw off temp readings..

Before you spend your birthday money on a shop, remove the new fan clutch and exchange it for a another new one. All you have to lose is a couple hours of your time. My fan clutch was bad for a long time (it worked a little bit before) but this recent heat wave really pushed it over the top. From what you are describing, it really sounds like how my car was behaving a couple of weeks ago with the old clutch that worked a little bit (like at morning start-up and on brief intervals thereafter) but didn't engage nearly enough like it does now.

Before you spend your birthday money on a shop, remove the new fan clutch and exchange it for a another new one. All you have to lose is a couple hours of your time. My fan clutch was bad for a long time (it worked a little bit before) but this recent heat wave really pushed it over the top. From what you are describing, it really sounds like how my car was behaving a couple of weeks ago with the old clutch that worked a little bit (like at morning start-up and on brief intervals thereafter) but didn't engage nearly enough like it does now.


Thanks for the encouragement guys, Its a big help. ok from what u guys said i think im still on track.

Yes New rad cap, i got it along w/ a t-sat when i did the manifold gasket.

The pump test, I will give it a shot in a day or 2 when im able to devot a good portion of a day running around my car.

I didnt put the front of the car on ramps. I will try that when i burb the system again.

Yesterday when i put the new t-stat in. Used the hose, And shot in the hose going TO the heat core, It came out, on the top of the t-stat whole i think. And then the TO heat core hose hits the engine. I shot water down there I think it was the water pump i forgot where it came out at but i think i flushed most of the compents fairly well. I did take the over flow out and cleaned that along with hoses, The inside of that bottle was all gunked up. I did that about 4 months ago its still clean. But i blew the hoses out again yesterday.

When i burbed it i used all antifreeze, No water.

RTV, I used the whole little tube they gave me in the felpro kit. I have my own i was goign to use. BUt the amount they supplied me w/ was what i would think to be just enough.

Im still not sure about the fan clutch, because i havent had problems with it before. But i think after the manifold. Once i cleaned it, In an assumption i would think now coolant is flowing though whole engine now. When i took off the manfold, the front driver side colant port on the cyl head was pretty well gunked up.

As for the water pump, I would think it would be pumping fine. When i was burbing it, And the t-stat opened, The flow of water hit about middle of the battery. or would that be more pressure then water pump?

When i was getting the t-stat, I was talking to the guy about my problems More or less the air in the system. He told be If i get longer hose running from the engine to heat core, And put a loop in the hose. Thats the way to fix it. He said the air will get traped in the hose and stay there. I wanted to know if any of you guys herd about that. I dont know how well it would work. theres still air in the system it doesent get removied just tapped like the heat core.

They should put like a bleeder on the damn heat core. Just like brakes that would make this simple

Loop in the Hose? That's a new one. I don't think so. YOU DON"T WANT AIR IN THE SYSTEM, TRAPPED OR NOT, PERIOD.

Let's review. New T-Stat, installed with spring down. New Rad Cap. Flushed radiator, engine and heater core. Fresh diluted anti-freeze. Pump that appears to be working. New fan clutch with the blades installed properly. Overflow tank and all hoses seem to be clean and open.

Either your not getting air through the Radiator or the water is not flowing through the radiator. I'd try the Ramps and Burp thing again and since you probably got some kind of warranty with the fan clutch, take it back to the parts store and get a new one. If neither of these things correct the problem, I'm thinking bad water pump or clogged Radiator because the water must not be circulating.

This is an air problem for sure.

Every morning you should check the coolant level in the rad when the truck has never been run and burp the system as much as possible.

This is an air problem for sure.

Every morning you should check the coolant level in the rad when the truck has never been run and burp the system as much as possible.


I checked it this moring. Everytime i check it, The level is just flush w/ the cap When i checked it today a lil bit came out. SOOOO i guess im on the right path for burbing it. I ran it hard today and there was some improvement. Normal running w/o a/c was a hair over 210, w/ ac was at 235 ish.

Fan question??? When i first start it up and go, The fan's on for about 30sec and shuts off. After that it will never turn back on. I noitce that by sitting and bringing, the rpms up to like 2500, the motor will get hot, like 220 ish and the fan will not kick in NOW if i let the rpms drop to idle, then bring it back to 2000-2500 and let it sit there the fan will kick in for about 5 secs then kick off. I would assume from hearing what people are saying about there fan clutch is, May be mines just not working correctly? I think the mix of air in the system, fan clutch, antifreeze/water mix and the CRAZY heat all just boil down to me overheating.

I wont have a chance to burb it today (my 21st b-day) But tomorro i will try. Do you guys think or, kinda sure my fan clutch just isnt doing what it should when it should. I could care less if its on 24/7, I can fix that by turing up my system. I cant however turn down the heat. I never had a DOA part before. What are your guys fan doing? What temp do they kick on at???

And I was thinking of a way to possibly build in a breather for the coolant system to bleed the air. Would it be possible to get like a bleeder valve, Stick it in a t-fitting and just run the motor and hold that down till antifreeze comes out. The air woudl come out, and get replaced with antifreeze from the reservor. If that would work, Less mess and way easier. If so were would be a good loacation to put one in at in the system.

Man, GO GET A NEW FAN CLUTCH!

Definitely a bad fan clutch. Mine was pretty much engaged full time this afternoon as yours should have been since you only live about 20 miles from me. The way your fan is behaving is exactly like mine before I replaced it.

Definitely a bad fan clutch. Mine was pretty much engaged full time this afternoon as yours should have been since you only live about 20 miles from me. The way your fan is behaving is exactly like mine before I replaced it.


I called advanced auto, where i picked up the clucth they said rip off and bring it in. So that will be first thing to do 2-morro. Ill pop it in and see what happens. Its only a week old so well see

But if it is overheating on the highway, it is not the fan clutch.

The fan freewheels when going at highways speeds.

But if it is overheating on the highway, it is not the fan clutch.

The fan freewheels when going at highways speeds.

But it should engage when it gets hot though right. Like when it hits 230 ish. Shouldnt it engage to kool it down? no matter how its being driven, town or highway. Even though high will kool off the rad just from driving, its got to have somthing more. I did here a slight gurgle when i made a right turn today. So some buring its still needed. i just got get it ALL the air out.

Where did you use the RTV? It's only supposed to be used on the front and rear of the block in between the gaskets where the block and intake mate. Either way, I never use more than half the tube. I doubt that's your problem, but.... As a side note, the only time I heard my fan was startup, and after sitting in traffic.

Where did you use the RTV? It's only supposed to be used on the front and rear of the block in between the gaskets where the block and intake mate. Either way, I never use more than half the tube. I doubt that's your problem, but.... As a side note, the only time I heard my fan was startup, and after sitting in traffic.


it came with a tube about 2-3" long that was like 1/2" think. A very small ammount, And yes just on the front and back of the motor conneting the gaskets together. im not worried about the rtv, i have no leaks and the oil is fine. I dont think thats my problem.

:banghead: Nothing. I put in the new clutch and it still overheated/. Spiked to 260 and ran terrible. I took out the drive side head light to get some colder air to hit the kone filter. I also stoped at a car wash and just hit the radiator with the hose for like 3 min its drop the temp down to like 130. So now in have no idea what it is, Bad radiator. I also did burb it again.

:banghead: Nothing. I put in the new clutch and it still overheated/. Spiked to 260 and ran terrible. I took out the drive side head light to get some colder air to hit the kone filter. I also stoped at a car wash and just hit the radiator with the hose for like 3 min its drop the temp down to like 130. So now in have no idea what it is, Bad radiator. I also did burb it again.

Can you tell if the coolant is circulating in the system? Since you eliminated the Clutch as the culprit, about the only thing left is poor/no circulation. Either the water pump is not pumping, or the Rad is plugged. When you burped it, did you get much air out? How much more coolant did it take?

Can you tell if the coolant is circulating in the system? Since you eliminated the Clutch as the culprit, about the only thing left is poor/no circulation. Either the water pump is not pumping, or the Rad is plugged. When you burped it, did you get much air out? How much more coolant did it take?


Well the thing was it was werid when i burbed it. I jacked the front of the car up so the rad is the highest point. I did it when i twould cold, I had it held at 3000 rpm the aint freeze sunk. I got a very small amount in then the t-stat opend. And it didnt gush out like it did before. There was 3 preety strong small streams that shot verticle across. It wasnt shooting out though. At that point i tied to pour some in, and the streams of anitfrezze shot it right ouw. But it wouldnt over flow. What im gonna try is in my heatcore return i still have my t-fitting in from my flush. Im gonna open that and run it and hopfully that will be able to burb it better. I thinking now my rad is shot. not sure Also today was all normal driving w/ a mix of a/c on and off

:2cents: I had this same problem about four years ago on my '88 4x4 5.0 worried me plum gray headed. It would run up to 210 stay there about 10 or 15 sec drop like a piece of lead run up to normal stay a minute run back to 210 or right at the red and drop again. I went through about five Tstat,burped, flushed, backed flushed, took my rad to have it flushed and the the guy told me it was a waste of money that type Hardly ever gets clogged up. So I checked it after I put it back on and the flow was good. I still don't know to this day what fixed my truck,if I finally got a good Tstat, I finally got the air out, or all the flushing and back flushing got the gunk out of it because it don't and has not ran hot since then.

have you tried a Prestone Acid Flush ?

at this point, I'm thinking heater core clog or rad clog or maybe even something going back to your original intake manifold repair ... perhaps some RVC/gasket blockage ?

did you pull your water pump when you had the fan clutch off?









Well the thing was it was werid when i burbed it. I jacked the front of the car up so the rad is the highest point. I did it when i twould cold, I had it held at 3000 rpm the aint freeze sunk. I got a very small amount in then the t-stat opend. And it didnt gush out like it did before. There was 3 preety strong small streams that shot verticle across. It wasnt shooting out though. At that point i tied to pour some in, and the streams of anitfrezze shot it right ouw. But it wouldnt over flow. What im gonna try is in my heatcore return i still have my t-fitting in from my flush. Im gonna open that and run it and hopfully that will be able to burb it better. I thinking now my rad is shot. not sure Also today was all normal driving w/ a mix of a/c on and off

have you tried a Prestone Acid Flush ?

at this point, I'm thinking heater core clog or rad clog or maybe even something going back to your original intake manifold repair ... perhaps some RVC/gasket blockage ?

did you pull your water pump when you had the fan clutch off?


No i didnt I didnt think there was anything wrong but a manifold leak. I dont know how the rtv would block annything it was wasnt close to any of the ports. Im leaning torwrd the radiator right now. When i flushed and back flushed it. The water came out reall hard. I was using a normal house spicket and a it came out of both ends of the core like it did the hose its self. May be it is the rad. Whats the best way to flush or test it. Would it be eaiser to pop for a new one and cancle any "did i flush it good enough" ideas.

BTW thanks soo much guys for your help. Slowy im getting there you guys are saving me alot of money again.

This sure sounds like a poor circulation problem. Early on you talked about bright orange Coolant in the Rad, while the coolant in the T-stat housing was clear. Either the coolant is not circulating, which means a bad water pump, or there is a blockage of some sort, a plugged radiator or something.

I haven't completely dismissed the possibility of air in the system yet.

Remove the rad cap and run the engine and watch to see if the coolant is circulating. Is there any possibilty that the water pump is choked with crud or damaged? You might try removing the little by-pass hose and flushing the water pump and block again.

What about the radiator, you might try to flush the T-Stat side by removing the upper hose and using the garden hose and rag method in the filler neck and back flush any crud out of the drivers side of the rad.

I think the thermostat is not opening enough.

Defective stat in my mind.

That's what I did to my '88 PU I backed flushed the Rad and the block like Rick was talking about and got all kind of gunk out. Like I said in my other thread I don't know what I did but it fixed my truck from running hot.:screwy:

I think the thermostat is not opening enough.

Defective stat in my mind.


U read my mind. I drained the rad today to see if anything came out. Very orange and not to much gunk at all. While i was there i took my t-stat out and boiled it it opend around 210, and when it opened it only opend about 1/8" from looking at the side. I pulled it apart and theres like 1.5" of travel there so i got another one (4 t-stats in 2 weeks all stants) and boiled it. it open around 200 degress but still not very far. And it very slowy opened. Does any one know how far they are soppsed to open. and how fast.

When i took it out the antifreeze was more orange this time.

I filled up the rad w/ new dexcool and burbed it as best as i could( it was getting hot). I took it out it jumped to 210, stayed there for a bit when a lil over (15 degrees) came back to a lil over 210. and stayed for a bit. ( this is all w/ a/c on). Then i turned it off and climbed the biggest hill i could find and went about 3/4 throttle up it and drove around fairly hard and back up to 245 ish. and stayed there. i parked it and let it idle for about 15 min while i cleaned up and put tools away and looked at it it was at 225 ish. So it did cool down a lil. It never did that. So a slight improvment but i still got more to do. I guess its down to bad water pump or bad rad. thats really the only realistic thing to be bad. Im gonna drive around and burb it every morning and see what happens.

Good luck, you have done about every thing I did to my truck so maybe if is not the t-stat it might be the pump. Check for that good water flow in the rad after the t-stat opens.

Well, I had a freak thing happen to me about twenty years ago with a car that would'nt stop running hot, The inside of the lower radiator came apart and blocked the inlet to the block, letting only a small amount of antifreeze to pass through.
I would pull all the hoses off (Heaters and upper and lower rads) and replace them first before ripping apart the water pump. It's Cheap Insurance...

You have a very unusual problem on your hands and I'm out of ideas other than what everyone above said today. Just a mention that if you are driving and the temperature gets dangerously high again, you might consider dropping your windows and cranking up the heater full blast. It's usually good for a 20 degree drop -- better a little sweat than a fried engine. (I'm still curious as to why with all that engine heat that your fan clutch is not engaged 100% of the time at lower RPMs). Keep at it and good luck. I can hardly wait to see how this is ultimately resolved.

1. So, no air then have you put a pressure tester on the system and does it hold pressure. Rule this out and the head gasket. You can leave the thermostat out and see if that helps the temp as a test.
2. When the thermostat opens, with the cap off, and you give it alittle throttle, do you see the water flowing a good rate in the radiator. If not then a water pump is about $50. so change it - if over 100k its nearing its life anyway.
4. Finally, a radiator is $160 and they do clog/corrode in the tubes. If Dex and air were in there you can try a chem flush but that usually takes the heater core out and that is a pain behind the dash, so....

1. So, no air then have you put a pressure tester on the system and does it hold pressure. Rule this out and the head gasket. You can leave the thermostat out and see if that helps the temp as a test.
2. When the thermostat opens, with the cap off, and you give it alittle throttle, do you see the water flowing a good rate in the radiator. If not then a water pump is about $50. so change it - if over 100k its nearing its life anyway.
4. Finally, a radiator is $160 and they do clog/corrode in the tubes. If Dex and air were in there you can try a chem flush but that usually takes the heater core out and that is a pain behind the dash, so....

Did you ever test the system with a pressure tester? I saw where you put on a fan clutch, where did you get it? The one I got from Advance was no good I went to NAPA spent a little more it worked.

Here's a quick and dirty way to check radiator performance that I pulled off another board. It's not necessarily a definititive test, but it might help:

"To check rad performance [in your back yard] you can drive until your
vehicle has reached normal operating temperature and then mist the rad with
water. If all the water evaporates then the rad is probably alright [as in
not blocked]. If there are areas where the water evaporates and others
where it doesn't [cold spots, usually vertical sections of the rad] then
the rad needs to be serviced [power flushed or rodded-out]. You can also
check for cold spots by using your hand but there is often not a lot of
space between the grille and the rad --> and you could burn your hand. Be
careful."

Did you ever test the system with a pressure tester? I saw where you put on a fan clutch, where did you get it? The one I got from Advance was no good I went to NAPA spent a little more it worked.


Yea i got mine from there. I get all my parts from there and really havnt had a problem with them. I hope i didnt get another crap clutch along w/ the 4 t-stats.

No, i didnt pressure test it yet. My buddy has one and i yet to go over and pick it up and try it. Hopfully i can do that 2-morro.

I am seeing an improvment thought. I hit 210 failry qucikly but i guess the t-stat open and it droped to about 190 ish and stayed there. that was only a short and easy drive w/o a/c. so i wont get my hopes up yet.

I took some temps from the rad. When idle w/ a/c for 15 min the car leveled at one small dasher colder then 210

Passenger top- 152
Passenger bottom -113
driver top - 125
driver bottom - 117
middle - 112

So i have a heat diff some top to bottom and side to side on the top. they were taken w/ a meat thermoter, And i VERY carefully stuck them in the fins of the rad with the car idle. those number show me a little. but may be to some who know more about rads, that would be my problem, ors its normal. I will try to get it hot and check it again.

what brand of thermostat are you using?

what brand of thermostat are you using?

Rad cap and t-stats are all Stant. i did get them from 3 differnt stores. They all have there own name, Napa, advanced, national. But they all have stants name on the box. All of them were 195 temp. I asked if they had a lower one, but they all told me theres only one for the 4.3 and its a 195

Same ones I used after I bought one that had a LIFE TIME GARROTEE on it was not no better than the rest.

Same ones I used after I bought one that had a LIFE TIME GARROTEE on it was not no better than the rest.


And i never seen another brand. I dont ask for them they all only stock stant. If they would have given me somthing diff i would have asked for a stant.

When it comes to thermostats, I always use GM..

I agree with Muddog, try running without a T-Stat. Years ago in OLDER 1960-ish trucks (Pre-Emission Control), I ran without the T-stat all of the time. See if this helps, if it does, I'd keep shopping for a colder thermostat. You should be able to find a 180° T-Stat for your truck, BUT DO NOT BUY ONE COLDER THAN 180° or you'll really open up a can of worms.

I live just outside of Phoenix Az, we see outside 100° temps everyday. In my 2000 Jimmy (and 2001 S-10 Blazer), I run a 195° T-Stat and my Air cond. all of the time and the only time I run above the 210° mark is when I'm stuck in rush hour traffic a 4:00 in the afternoon. I had my system reverse power flushed last year and run 50-50 Dexcool. As a comparison, Your truck should not be running that hot.

I just dropped a stat into a pot of boiling water and it opened up quite a bit.

I have to replace my stat tomorrow.

It will warm up, open up and then won't close back up which has the engine running quite cold for a while before the stat will close up a bit. Just wasting gas not changing it.

I just dropped a stat into a pot of boiling water and it opened up quite a bit.

I have to replace my stat tomorrow.

It will warm up, open up and then won't close back up which has the engine running quite cold for a while before the stat will close up a bit. Just wasting gas not changing it.

U think we have the oppiste problems? mines not opening enough, and urs is opening to much/not closing?. When yours opened how far did it open. For me looking at the side where the plunger would move down, there was a very small gap from the top of the plunger and the bottom, of the top of the t-stat, almost like 1/8" I asked some people at carsense and when i asked them they all looked at eachother and scratch there heads.

U think we have the oppiste problems? mines not opening enough, and urs is opening to much/not closing?. When yours opened how far did it open. For me looking at the side where the plunger would move down, there was a very small gap from the top of the plunger and the bottom, of the top of the t-stat, almost like 1/8" I asked some people at carsense and when i asked them they all looked at eachother and scratch there heads.
The one's I was having problems with when I was having my problem since I don't throw nothing away, all four of them was not opening all the way when put in boiling water. I dug them out of the tool box last night and made some t-stat soup today. I noticed on two of them the reason they was not opening all the way the valve was binding and twisting so I worked and piddled with one smoothed the edges retested it works fine now.

O.K. Here is the big question for all of you experienced wrench twisters out there. And I almost hate to even ask it.

Is it possible to put the intake manifold gaskets on backwards or upside down and block the water ports and thus restrict or stop the coolant flow? I am being told that this is very possible. Even to the point that the bolt holes will still line up but the coolant ports won't.

I think after all this poor guy's been through, we'd have tripped over something by now.

Oh and BTW I just went down and bought a brand new 195° T-Stat and threw it into a cup of boiling water and it didn't even open at all.