# Overheating diagnosis



## Huge29 (Sep 17, 2007)

So, here is the situation with my neighbor's '01 Caravan 3.3L engine. It starts overheating all of a sudden one night. The obvious issue seemed to be the thermostat, changed that and no change; I even tested the old one in a pot and it was working, I rechecked the new one and it was to. So, as it is overheating the radiator cap is not even warm, but the upper rad. hose feels like it is about to explode as it is under a lot of pressure. Seemed as if there was a blockage in the radiator; no leaking anywhere under the car, so water pump appears to be fine. Popping the cap does show that there is pressure, so the rad. cap appears to be working also.
It has already been fixed, but I am curious to know how the issue created the symptoms, so give it a try; it sure surprised me. 
Again, not the water pump, rad. cap, water pump or thermostat.


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## luv2fsh&hnt (Sep 22, 2007)

I had a similar situation with an 87 honda accord. I also assumed the thermostat still overheated. I flushed it twice and it quit overheating.


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## .45 (Sep 21, 2007)

My guess would be a blown gasket on the intake manifold, or a warped manifold...or both. Worst case could be a crack in one of the heads. Got any heat coming out of the heater? See any burnt water stains around the intake? Surprisingly, some of our local 'tune-up' shops can diagnose these problems quite well.....sometimes.

I'm curious....keep us posted !!


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## truemule (Sep 12, 2007)

Possibly a bad oil pump or very low oil causing the engine to heat very quickly and causing the over tempurature, but the cool water in the radiator kept the thermostat from opening completely because it kept it cool. So the therostat always thought it was cold but the engine was making to much heat.


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## phantom (Sep 13, 2007)

I had a overheat issue on an Acura which I thought was going to be major. The dealer fixed it in about 1 minute, a vent hose problem


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## mikevanwilder (Nov 11, 2008)

I had a problem with my '98 chevy cav, as long as I was going over 50 mph it was fine but if I slowed down for to long the guage would climb. I went through all the checks and it continued. So I did what L2H&F did and flushed it twice and the problem was gone. This was after about 140k on it.


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## Huge29 (Sep 17, 2007)

Well, I wanted to hear other's thoughts before I disclose what the garage said; .45 was closest. They said that it was the head gasket, but I have a hard time believing that. There was no oil in the AF and no AF in the oil; isn't that the one sure sign of a bad head gasket? I think it was something else and they charged for the most expensive repair they could possibly justify IMHO.


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## luv2fsh&hnt (Sep 22, 2007)

Huge it is very possible the head gasket was bad without the AF and oil mixing. Alot of times unless there is a total catastrophic failure of the gasket the fluids won't mix but there is enouph loss of pressure to not allow the thermostat to open which will cause the overheating.


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## Huge29 (Sep 17, 2007)

Thanks for the input. Please help me understand how the head gasket could be the culprit! The radiator was still under pressure and the upper hose was under a lot of pressure... When we took out the new thermostat to check it it was so hot that it was still open even though the AF had just drained out, so it was definitely open and there was pressure at least in the radiator. Not my car, I am just curious. Additionally, this is my neighbor and we have the nearly identical van, Just had to change the water pump two months ago, we same to have the same problems within about a month of each other, so I am just wondering what is next. Before April and after 110K miles, had not had a single repair other than the battery, so it has been very good to us.


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## luv2fsh&hnt (Sep 22, 2007)

You are dealing with very high pressures and what amounts to a pin hole leak can cause a great loss of pressure and at the same time the liquids aren't able to escape because heat causes expansion. Basically liquid molecules are much larger than what is essentially steam molecules after the overheating begins. The thermostat would still be very hot but not open due to the pressure loss because of heat transfer. Was he experiencing a loss of coolant without an obvious leak or could he smell coolant after shutting the motor off without an obvious leak?


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## mikevanwilder (Nov 11, 2008)

Could you smell AF coming from the exaust? That is a sure sign that the head gasket was gone. I know what you mean by the mechanic charging for the most expensive thing, I had a old geo tracker and the thing started to act up and not run very well. It eventually quit running altogether. I was at work so I had my father come and get it. He took it to a mechanic and they told me to call in a day or two and they would have the diagnoisis. Well I went in two days later and the guy says oh yeah your head gasket is blown. I was like really I didn't notice any signs of a blown head gasket. I asked if I could see the head and gasket to see for myself. He said that they haven't even looked at it yet but that was what they assumed was wrong. I told him maybe before he tells someone whats wrong with a vehicle they should actually work on it first. Turns out I had 2 plugged fuel injectors. $80 dollars later and it was good as new. Instead of the 1500 they told me is what I was going to have to pay.


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## yfzduner450 (Dec 28, 2009)

I would of bet a intake manifold gasket too. They are a weak spot on the 3.3L. Also i had a blown head on a chev 350 once and had no af/oil mix and tons of pressure, it was too much pressure and that's how we found out about the head gasket. Cars can be a pain in the butt some times.


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## guner (Sep 25, 2007)

Just throwing in my 2 cents..... I had a 2000 1500 that had the same things going on, intermitantly, then was pulling a trailer (only 2000 lbs) and burned up the engine. I still had it under warranty and they replaced it.... I had less then 100 miles on new engine and it burned up also. when they towed it in, the Dodge guy said that there was a known issue with a certain group of engines in dodge and both engines I had were in that series. I asked why they wouldnt have checked that before install, he didnt have an answer. The day after I got the truck back I took it in and traded for a Chevy.


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## Huge29 (Sep 17, 2007)

luv2fsh&hnt said:


> Was he experiencing a loss of coolant without an obvious leak or could he smell coolant after shutting the motor off without an obvious leak?


No, yet another reason for my confusion. No smell in the cab-not heater core and not low on AF...


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