A Severe Overheating Problem -1995 Jimmy (I did a search – no help) - Anyone

I’ve read at least 20 Threads on the board about overheating, but haven’t seen an answer that fits my problem.

I have a 1995 Jimmy 4x4, with 100K miles on it. The overheating problem started 2-summers ago when I flushed the radiator myself. The coolant looked ok, no sludge, still looked green, but I thought it was time for a coolant change. It had about 85K on it then. I used a fast flush I got from the local parts store, followed the directions, then stuck the garden hose into the radiator, wrapped a rag around it to create a little pressure and let it run for 2-3 minutes with the drain plugs open on the block and radiator. I refilled the radiator with 50/50 green antifreeze and water, plus I added anti rust inhibitor.

From that point on, when the outside temperature is 90 plus I have an overheating problem. Not too bad on the highway, but in the city with stop and go traffic it will peg the red line on the heat gauge. If I don’t run the air conditioning, or if I run the heater it helps. When the outside temperature is 70 degrees or less - no problem. 80 degrees outside and it runs warmer than it should.

Here’s what I’ve done in trying to find a fix. Replaced the thermostat with a 180, replaced the mechanical clutch on the fan with a heavy duty type, replaced the fan belt, replaced the radiator cap with a Stant 14 psi vented, took the radiator to a local radiator shop and had it checked out. He said he ran water through it with his power washer and it seemed ok, not plugged up. I parked it on a 30 degree slope and let it run for about 30 minutes. The thermostat opened up, but no air seemed to come out. None of this helped – still overheating into the red in town and the gauge running ¾ the way over on the highway. The radiator is full to the brim when I take the cap off. I can hear the mechanical fan kick in, but it shuts down when I reach a speed of about 35-40.

I installed an 11-inch eclectic fan on the inside of the radiator and I run it in conjunction with the mechanical fan. This helps, but it still wants to try and hit red on the heat gauge when driving in stop and go traffic on 90 degree days. I have the electric fan set to come on at about 220, just above the half way point on the gauge and it goes off just under the half way point. With the addition of the electric fan on the highway when its 90+ the heat gauge runs straight up at the half way point, but when I stop at a traffic light it goes up to the ¾ mark, then back to the half way mark when I get back up to 60-65. I even popped the hood onto the safety latch to let air into the engine compartment while running down the highway – no difference. I visually inspected the radiator hoses when the gauge was at the ¾ mark and they didn’t appear to be collapsing. 2-summers ago I added a quart of "cool-it" I got from the auto parts store. This helped some, but not enough. Since then I've changed the coolant again.

There is no water in the oil, no gas in the water, no ugly looking antifreeze or bubbles or gunk or bad smell in the radiator or the reservoir tank, and it doesn’t loose any water, or use any oil. The Jimmy runs fine, no change there and it gets the same gas mileage as before, about 20 mpg on the highway.

I’m thinking there must be a restriction in the water flow, or the water pump is not doing what it should.

However, since the problem started immediately after I did the flush, it almost has to be related to what I did. When I flushed it I put a screen in front of the radiator to keep out bugs, maybe this is the problem. I will try removing it and see what happens, but I’ve checked the screen and it’s clear – not bugged up.

Does it seem possible that a radiator hose may have deteriorated on the inside to the point where a flap is blocking water flow?

I wouldn’t hesitate to replace the radiator, if I thought it would solve the problem, which seems like the next logical step.

Any suggestions will certainly be appreciated.

Thanks in advance,

DelCoch

DelCoch, very good post about your problem. I have to say it sounds like you covered about every possibility but I am sure others will chime in if something was missed. One thought came to me while reading your post. Have you thought about your temerature gauge. Could it be bad? I am wondering if there is a way to check the gauge to see if it is reading too hot. I have driven a too hot truck before and believe me you know something is very wrong. My .02. I am sure others will chime in. Good luck.

Charlie M.
Dallas

Charlie, Thanks for your reply.

I thought about the heat gauge not being accurate, but the electric fan has an adjustable thermostat for on and off, labeled like 160-220, which seems to be in correlation with the heat gauge. That is, if I set the fan to come on at 180 it comes on when the temp gauges says 180, same when set at 200 or 220. I’ve never let the radiator boil over; when it gets to the red I do something to cool it down.

I also thought about not having a heavy enough mixture of antifreeze, as at first it tested at -15, so I added more antifreeze to get it down to -25. I would think this would be good, maybe not.

I’ve also noticed the mechanical fan doesn’t really start getting in the act until the heat gauge gets well past the half way point. (I can hear it kick in when setting at a traffic light) I think this is normal, but again I’m not sure. The electric fan kicks in first and it may be somewhat cooling down the sensor on the mechanical fan.

I also thought about having an overcharge on the air conditioning system, but I had to replace the compressor on it last fall and I made sure it reads what it should on the gauges.

I’m sure I’m overlooking something, somewhere, but I don’t know where.

DelC

How does the cooling fan know the temperature? Does it connect to the vehicles sending unit? If so your sending unit may be bad and you are not actually running hot.

Water pumps have a little feature called a weep hole to let you know when they should be replaced. Do you see any coolant dripping from behind the water pump.

Anything restricting the flow of air into the radiator will increase the temperature. You should remove the screen.

You should also put a 195 thermostat back in. Putting a lower thermostat in will do nothing to prevent overheating. Running the temperature lower than the factory setting will increase combustion by-products in the engine causing increased engine wear.

You need to replace the rad cap with a 16psi Stant. It should have came from the factory with a 15psi cap, you should never go lower than what it came with considering that every 1 pound of pressure increases the boiling point of the coolant 3-4 degrees.

Change the water pump.
The vanes (impellor) in the water pump do corrode over time. When I changed mine with a new one from Autozone, there was a warranty disclaimer in the box stating that corrosion of the impeller blades was not covered without using a specific mfg # of antifreeze. They would still cover the more commonly-known water pump failures "leaking shaft seal". Disolving impellor blades will not produce a telltale leak in the weep hole.
It is only about $40 and easy to change. This is a much better bet than buying a new radiator.
__Also check to make sure a previous owner has not installed underdrive pully on the water pump. Common underdrive pulley will decrease the coolant flow by 14%. You need 100% of what GM dsigned in to cool when ambient is 90-100F.

heater core?

reverse flush?

How does the cooling fan know the temperature?
Do you see any coolant dripping from behind the water pump.
You should remove the screen.
You should also put a 195 thermostat back in.
You need to replace the rad cap with a 16psi Stant.
The cooling fan has its own sensor, which I installed inside the left radiator hose at the radiator. I have no coolant leaks. My mistake on the radiator cap and thermostat; I just double checked and the cap is a 16 psi Stant, which I just replaced last week after seeing it as a suggestion for someone else on this board. I still have the box for the thermostat, which I replaced 2 summers ago when the problem first started. It’s a Stant # 13849 – S 384 195. Which probably indicates it’s a 195. I defiantly will take the screen out tomorrow.

Change the water pump.
__Also check to make sure a previous owner has not installed underdrive pully on the water pump.
I'm the original owner - no modifications on pulley.
I’ve been thinking about replacing the water pump, but since there was no problem before I flushed it I can’t see it becoming corroded in a period of a few weeks. If the fins are aluminum, I guess the fast flush could have eaten them. I was thinking the fins were steel, or something.

heater core?
reverse flush?
I doubt the heater core is plugged. When I run the heater it helps cool the engine, which means the heater fan is cooling the coolant as it passes through the heater.

I going to take the screen out tomorrow and if that doesn't solve the problem the next step will be replacing the water pump. I've been leaning towards the water pump since the beginning, but I didn't realize the blades could be corroded or eaten alive. I guess the blades must be aluminum, huh?

Thanks for the suggestions. Please keep them coming.

I'll let you know any results, good, bad or no change.

DelC

I would agree on the radiator being the final option with all that you did... But for giggles, I would back flush the heater core. (pull the hoses and run good amount of water pressure through it)... Please let us know how it turns out!

As others have said, you've done a pretty good job of troubleshooting and tried everything we would. How bout sitting back and tracing the heat path in the engine to see where heat goes, and maybe why it's not getting there.
The engine burns fuel to create prower and heat, the cooling system extracts the heat from the engine and delivers it to the radiator which dumps it into the air flowing over it. The radiator is designed to deliver all of the heat from the engine, oil cooler, and transmission cooler while using air heated by the air conditioner condenser. It does this on everyone elses truck, what's wrong with yours?
You say that going faster cools the engine, because of increased air flow, running the heater cools the engine, because of extracting heat through the heater core, turning off the AC cools the engine, because the air getting to the radiator is cooler and extracts more heat. Sounds like the radiator isn't doing it job of getting rid of the heat your generating.
I had the same problem on one of my vehicles. I had a cronic hot day cooling problem, when I climbed the hill to my house I could hear the coolant boiling in the block. One day I got the hose out and sprayed the radiator while the engine was running, it cooled down to normal fairly quickly. I shut the hose off and went to get ready to attack the car, when I returned the hot radiator had dried, well almost. The top of the radiator was almost dry, but the bottom was still wet. I started the engine, disconnected the electric fan and cooled the radiator with the hose. I then checked the radiator, it was hot, but about 2/3 of the way down it was cool.
I replaced the radiator and the overheating stopped. I unsoldered the old radiator and found the bottom third of the tubes were completely plugged. The flow was adiquate in the upper 2/3 but the bottom 1/3 of the radiator was inert. I rodded them out and they were plugged from one end to the other.
Our cooling systems are designed to handle the heat load on the hot days we have, the radiator should be able to handle it all plus some, but not if its plugged.
Some times we just have to bite the bullet and change a part because it can't be anything else. If you change the radiator, take some more heat out of the engine, replace the radiator mounted oil cooler with an external one, same with the transmission cooler. I have a transmission cooler on my Yukon and it never get's above 160F even on 110+ days, that's got to be good for the transmission.
Hope this helps.
94

Some times we just have to bite the bullet and change a part because it can't be anything else.
That's been my thoughts too. The thing with the radiator is; I took it to a radiator guy that I half way trust, he took the tanks off and sprayed water though the core with a power washer and said it wasn’t plugged up. I thought for sure I had caused it to plug up when I tried to back flush it with the garden hose. If a larger capacity radiator was available I would have replaced it by now. But, it seems the only radiator available is just the standard factory type.

I do have a transmission cooler, which was added after the transmission got too hot while towing and blew the seals. This was long before the current problem developed. One problem there though, the transmission cooler sets in front of the radiator and air conditioning cores, which probably blocks some of the air flow.

When I removed the radiator to take it to the shop, I found about 2-inches of bugs stacked up on the top portion of the radiator, between the cores of the radiator and the air conditioner. I thought I had found the problem then, but no. That’s why I put the screen in front of everything.

I’ve now removed the screen; I just need to wait for another 85-90 degree day to see how it does. I have my trusty 88-95 Hanes manual, plus the 300 dollars worth of original factory repair manuals, so I will see what it’s like to pull the water pump and take a look at the fins on it. I guess I just as well replace it once I have it off, regardless of what it looks like.

Thanks for the reply - other suggestions are welcome,

DelC – ‘95 Jimmy

Ok, I replaced the water pump. 30 dollars and change, and some 4 hours later I found there was nothing wrong with my old water pump, at least not that I could see. I removed the backing plate and took a look inside the old pump. The fines on the propeller are not aluminum; they are metal and look like about 8-gauge sheet metal. There was no corrosion, or gunk. It looked really clean.

However, I did find the spring in the bottom radiator hose was extended up into the water pump about 3 inches. This probably wasn’t a problem itself, but it could have been letting the hose suck shut on the other end near the connection to the radiator. (Maybe) I had checked for such when the engine was overheating.

So, I topped it off with antifreeze again, got the air out and removed the bug screen, which was located between the radiator and the air-conditioning condenser cores. I will be taking a 1,400 mile trip with it this weekend. Be interesting to see how it does. Maybe I can get some of that 30 mpg gas mileage.

DelC 95-Jimmy

Look for a hose that collapse's under hot condition?

It happened to me old worn out hoses that loose their form from the inner spring being bad?

I ended up putting the old hose back on. Advance auto didn't have a new one. Actually, the old one didn't look that bad and the spring still looked good. I stretched the spring out to make it fit tighter. I’ll keep an eye on it, but I had checked it before to see if it was collapsing and it looked ok. So, we will see.

Well, the new water pump didn't help, nor did removing the bug screen. I still have the same problem of overheating when the outside temp is above 80 degrees.

I guess the next step is to set it fire and collect on the ins.

Well, the new water pump didn't help, nor did removing the bug screen. I still have the same problem of overheating when the outside temp is above 80 degrees.

I guess the next step is to set it fire and collect on the ins.

I reread your original post. You say that you have both a mechanical and clutch fan on the system. This could be blocking proper air flow to the engine. (do you still have the OEM fan shroud on?)

Did you ever try the back flush? When/if you do, remove the thermostat while doing it.

One other thought... Do you have access to a live scanner? The reason I ask is that it may be possible that your gauge sending temp unit may be bad. This can be confirmed by running a live feed on the ECM and seeing with the ECM temp sensor is sending out. I've seen this happen more than once.

My son has a live scanner, but he lives an hour from me. It will be a couple weeks before I will have a chance to run it on my Jimmy.

However, the electric cooling fan has its own heat sensor, which I installed inside the left radiator hose at the radiator. The elec fan is set to come on at 220 and go off at about 195, which is what the stock heat gauge reads when the electric fan goes on & off. Thus, I believe the heat gauge to be accurate. Plus, when the outside temp is 70, the heat gauge runs at 195 like it should. As I said before, it only overheats when the outside temp is 85 degrees or above. Yes, I still have the OEM fan shroud on.

Prior to adding the electric fan the heat gauge easily pegged out in the red in town and ran about 230 on the highway, when not running the air-conditioner. Adding the electric fan improved things, temp reads 230 on highway with air running and will go into the red in the city, but it no longer pegs out all the way. Since it improved the situation, I don’t think the electric fan is blocking air flow. (it’s mounted on the inside of the radiator) And, popping the hood onto the safety latch to allow more air into the engine compartment, when driving down the highway, has no effect on cooling.

Also, I don’t have fog lights or anything in the grill to obstruct the airflow.

I guess the only thing left is to try a fast flush and a back flush with the garden hose. Although I haven’t done anything to cause it to change, I probably should check the timing. It may have changed on its own and be a little advanced, but I doubt that. Or, I could ask the radiator shop to build me a bigger radiator. Other than that, I flat give up.

Does anyone know if a radiator for a 1998-2003 is any larger than my single core and maybe bolt into my 95?

DelC

have you checked your rad-to-overflow rubber tube?

I know mine was completely blocked with crud causing all sorts of weird problems temperature spiking problems. I completely took it off and had to ream it out with a coat hanger. I also reinstalled with some better quality hose-clamps.

good luck

How is the engine running? I have a 90 GMC K1500 that has been running warmer than I wanted it to. Not as warm as yours but warmer than normal. I have also been fighting a rough idle when warm. Recently, I replaced the pickup coil trying to find my rough idle. Right away, I noticed that the low end roughness was gone. I was also surprized that it started to run at the normal temp again.

I suspect that my rough idle/miss (I could see the miss with a timing light) was causing extra fuel to be dumped (since the plug was not firing) and the computer leaned out the fuel to compensate. Running leaner (I think) caused it to run hotter.

Something to look at when get it hooked upto a scanner.

//2000CAYukon

have you checked your rad-to-overflow rubber tube?
Yep, overflow tube is ok. The thing is, I never had any gunk in the radiator, ever. The coolant looked clean when I started messing with it. Guess I should have left it alone.

DelC

How is the engine running?
Engine runs fine - never misses a beat, idle is fine. Gas milage is where it has always been, 20 mpg on hwy.

Perhaps I missed it but have you checked your radiator for cool spots? And as for runniing a pressure washer through your radiator, this will not tell you if there is a partial plug inside. Water will find a way out unless the radiator is COMPLETLY plugged. When the radiator is warmed up you should be able to tell by touch if it is uniformly warm, if there are areas that are noticeably cooler than I would lean towards a partial block which will cause overheating at higher speeds.

Perhaps I missed it but have you checked your radiator for cool spots? And as for runniing a pressure washer through your radiator, this will not tell you if there is a partial plug inside. Water will find a way out unless the radiator is COMPLETLY plugged. . .
Maybe I didn't explain it very good, but the radiator guy took the tanks off the radiator and ran the pressure washer through the tubes of the core, and said it appeared to be fine.

I haven't checked it for cool spots, as there isn't room to get your hand between the radiator and the air conditioner core, and I have the electric fan on the other side. I guess I need an infra-red / laser type thermometer.

DelC

You said your antifreeze still looked green?Have you always had the green antifreeze?I was just asking this because if you ever had dex cool in the engine prior to the green and if the engine wasn't flushed good enough that maybe your problem..

You said your antifreeze still looked green?Have you always had the green antifreeze?..
Yep, it has always had green in it from day one - I'm the original owner.

DelC

I have been looking for days on the web, trying to locate someone else who is haveing the same overheating issues with a 4.3L GMC Jimmy. DelCoch's issues are identical to mine. My Jimmy runs entirely too well for this to be an unrepairable case. There has GOT to be a resolution. Please keep posting ideas. Would like to discuss via phone with Delcoch if possible before I lose my mind!

bgr8ful

bgr8ful,

I sent you a PM.

Dont see one. I thought I sent you one yesterday as well. Guess you didn't get that either. Email me at bgr8ful@sc.rr.com. Thx

I had a problem like this on my old astro 4.3. I flushed the antifreeze and after that I had a warmer running engine. It turned out to be my intake gaskets were leaking internally, the flush loosened up some scale build-up and caused a leak, but it was being burned off while driving. This leak was big enough to make it run hot, but not really big enough to see it come out the exhaust pipe(as white smoke). I replaced the intake gaskets, throughly cleaned the intake - problem was solved. It took awhile to figure out through, because i had no leak. Also like rilth said, ever try a good back flush of the heater core? You can by-pass that by disconnecting the lines and connect them to each other. Also did you ever get the system pressure tested? Did the rad itself get pressure tested at the rad shop?

I had a problem like this on my old astro 4.3. . . . turned out to be my intake gaskets were leaking internally, the flush loosened up some scale build-up and caused a leak . . ever try a good back flush of the heater core? . . . Also did you ever get the system pressure tested? Did the rad itself get pressure tested at the rad shop?
Internal leak is a good thought, as I do have a lot of condensation coming out of the exhaust when I first start it up. At least, I thought it was condensation, but now you got me wondering. The second muffler rusted out about a year after I started having the overheating problem. However, I never lose a noticeable amount of coolant.

I can't see where a plugged heater core could be a cause, as the coolant doesn't even attempt to flow through the heater core when the heater is turned off. Plus, when I turn the heater on it helps cool the coolant as it passes through the heater core. Also, if the heater core was blocked the heater wouldn't blow hot air.

Nope, no pressure test on anything, but I have a radiator pressure tester, so I will do a pressure test in a day or so. I do know the radiator has pressure when you go to take the radiator cap off when the engine is at operating temp, but maybe it don't have enough.

An internal leak into the intake is about the only thing that makes any sense, as I have replaced or checked everything else. But, I would think a coolant leak into the intake would make it run cooler, not hotter. Wouldn't the coolant leaking into the intake help cool the engine?

I must say I'm not a novice at mechanic work, as I worked as one for several years in my younger days, but I'm out of touch with current trends.

An internal leak into the intake is about the only thing that makes any sense, as I have replaced or checked everything else. But, I would think a coolant leak into the intake would make it run cooler, not hotter. Wouldn't the coolant leaking into the intake help cool the engine?
.

If you have a leak, or an opening in the system, it will not run cooler, but warmer because it would not reach its operating pressure, and therefore be ineffecient.