Topic: 2 weeks to the race and the car decides to start overheating...

Car seems to be running well, but it is overheating. Went out for an hour drive and it is losing coolant.

No white smoke.

Compression test is good.

Cooling system holds pressure.

I can't figure out where the water is going.

Car is a Dodge Caliber.

Any ideas?

2 (edited by TheEngineer 2020-09-11 04:17 PM)

Re: 2 weeks to the race and the car decides to start overheating...

Do you know it is overheating? Meaning you have verified through some gauge that the temperature is exceeding the point you want? Or are you just assuming because coolant is going somewhere?

As a quick note, the gauge on the dash is often not useful, they are programmed to stick the needle in the middle for a huge range of temperatures, and by the time it moves the needle to hot you're at a temp that you really don't want in a race car. Grab an OBD reader and pull up the actual measured water temp.

If you haven't seen evidence of the coolant going somewhere, have you had the system emptied at some point? and if so do you know you bled it correctly? Could it be that it's just burping all the air pockets out as you drive?


I would idle it in a driveway with the pressure cap off whatever tank is in that car. Watch the water temp on an ODB gauge. At around 180/190 the thermostat should open and you should see some evidence of increased circulation (feel the radiator hoses and one should go from cold to hot as it opens). Watch the coolant level, top it off as it drops. Hopefully it stops dropping at some point. If you can get it to stop dropping, and actually rise (as it heats up), put the cap back on and watch for it leaking somewhere as the system builds pressure. You can rev the engine to build more pressure with the increased pump speed too.

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Re: 2 weeks to the race and the car decides to start overheating...

How did you verify it holds pressure?  Did you use a pressure tester?  If so, did you test the cap?

Re: 2 weeks to the race and the car decides to start overheating...

I got an overheat on the freeway at 80 or so MPH, according to OBD it got up to 240F. I stopped and had it towed back to my house. When I checked it the next day, it was down half a gallon of coolant...it only holds 2 gallons.

I am certain the coolant was topped off before I started, I used a radiator funnel to top it, had the heater running while topping it, made sure it was up to temp, etc.

I used a pressure tester.

The cap is brand new, but it suppose it still could be the cap.

The coolant overflow tank was above the full line after the overheat, indicating that coolant was being pushed out.

Re: 2 weeks to the race and the car decides to start overheating...

I'm just guessing at this, but it could be a small head gasket leak, or worse, a small crack somewhere in the head.
As the motor gets hot, the crack opens slightly and builds up pressure in the coolant sytem, which would explain why water was pushed into the coolant tank.

Again, just guessing. I've had this happen to me years ago, and we found small cracks in the valve seat area.

Re: 2 weeks to the race and the car decides to start overheating...

Pessimist in me says some kind of head issue as well. 240 is HOT. You could have had a very minor problem and then it started a feedback look of it affecting the cooling system, which made the engine get warmer, which caused the issue to get worse, which sped up the affect on the cooling system, which sped up the worsening of the issue, etc.

When the head gaskets went on my WRX a few years ago the symptoms were that it would get hot at idle (but would be ok while driving), and it was pushing coolant to the overflow and then not drawing any back when turned off. I noticed the problem starting when my heat wouldn't work at idle, system had lost enough that the heater core wasn't getting enough flow at idle. There was a small point in the gasket where combustion gasses were pushing into the coolant passages and then pushing coolant out of the system.



Sometimes, depending on the design of your cooling system, you can take the cap off and watch for bubbles while the car is running. I could in the WRX because it has a small tank right on top of the engine that is the highest point in the system. I could see a regular interval of bubbles when running the car at idle. They weren't fast or large, but it was consistent



Not saying 100% that you have a head issue, just that the symptoms as you describe could match that problem. .

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Re: 2 weeks to the race and the car decides to start overheating...

I did more research on the engine, and I found that it has two separate cooling loops, one for the head and one for the block, and therefore it has two thermostats.

Found this in the factory service manual:

The head thermostat starts to open at 77° C (171° F) and is fully open at 89° C (193° F).
The block thermostat starts to open at 95° C (203°F) and is fully open at 108° C (226° F).

I'm trying to find a lower temp thermostat for the block.

I also found this little gem in the manual:

Thermostat failing shut is the normal long term mode of failure, and normally, only on high mileage vehicles. The temperature gauge will indicate this (Refer to 7 - COOLING/ENGINE - DIAGNOSIS AND TESTING).

Re: 2 weeks to the race and the car decides to start overheating...

Well, that's better news than what I was guessing... smile

Re: 2 weeks to the race and the car decides to start overheating...

dungeonracer wrote:

Well, that's better news than what I was guessing... smile

Yeah, I'm guessing (hoping) that the issue was caused by the high temp block thermostat. I'll pull the spring out of it so that it stays open, but still offers flow restriction. It might take longer to warm up, but it will hopefully stop another overheat condition.

So if I didn't do any damage to the engine from the overheat, it might be okay to race.

Re: 2 weeks to the race and the car decides to start overheating...

I hope that is the root cause.

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Re: 2 weeks to the race and the car decides to start overheating...

Limonaid wrote:

I did more research on the engine, and I found that it has two separate cooling loops, one for the head and one for the block, and therefore it has two thermostats.

Found this in the factory service manual:

The head thermostat starts to open at 77° C (171° F) and is fully open at 89° C (193° F).
The block thermostat starts to open at 95° C (203°F) and is fully open at 108° C (226° F).

I'm trying to find a lower temp thermostat for the block.

I also found this little gem in the manual:

Thermostat failing shut is the normal long term mode of failure, and normally, only on high mileage vehicles. The temperature gauge will indicate this (Refer to 7 - COOLING/ENGINE - DIAGNOSIS AND TESTING).

Remove both thermostats and move on.

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