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

[DelCoch]

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

[cmoore992002]

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

[DelCoch]

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

[blazee]

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.

[herkyhawki]

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.

[drdd]

heater core?

reverse flush?

[DelCoch]

Originally Posted by blazee

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.

Originally Posted by herkyhawki

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.

Originally Posted by drdd

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

[rlith]

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!

[94 Jimmy]

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

[DelCoch]

Originally Posted by 94 Jimmy

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

[DelCoch]

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

[lowrider67383]

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?

[DelCoch]

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.

[DelCoch]

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.

[rlith]

Originally Posted by DelCoch

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.