hacker-pschorr

Is this a bad time to mention it's absolutely possible to have a coolant leak that only shows up when the engine is hot?
Reason why those pressure testers are not absolute.

Same with compression tests. We had an Audi with good compression across all 5 with bent valves. Leak-down test confirmed the damage.

That's the problem with your Q&A, you are looking for absolutes in a wold with many gray areas.

What concerns me and many others is not what caused the issue, but what may have also been damaged as a result of the high engine temps mixed with areas void of coolant while at these high temps.

Lizard928

Am I the only one that thinks starting the car with a noisy WP bearing is a stupid idea?!

Fix the WP first. Then test further!!!

If it is the headgasket, which is the first thing to hopefully go when overheated, it very well could only show up under random circumstances.
The random bizarre things you see when fixing cars daily is astounding.

mark kibort

Just got done with a compression test.... for Eric... actually, heck, im not going to leave any stone untuned.

all plugs look great. compression 190 190 190 200 on on the passenger side.

hacker-pschorr

That's the first good news you've reported. A washed out plug should be rather obvious....

I feel better now, time to take the pump off.

mark kibort

im with you on all counts Eric... this kind of stuff scares the XXX out of me!

thats why i did the tests on monday, getting it to temp and driving it around , then turning the fans off to get unusullly , high, but stilll safe temps in the motor and check for leaks. nothing was found. car runs fine, fans cycle as normal (with only one fan) and takes a little beating on the street with no issues or leaks. the only thing i have to go on now, is that it HAPPENED and i dont know why other than two clues... noisey water pump and voids of air in the engine with flacid hoses after the race .

I agree, but part of me thinks that we need to check other things first , and while things are hot too to try and approach the conditions where the issues occurred. i have a feeling that the the problem was my fault due to not slightly overfilling reservoir and bUrping the system. maybe the water pump being run dry at high temps caused it to have the , seemingly minor bearing failure. (serous failure is much more noise and leaking through the bearing as the last 8 year old lasso did at the end of last season as i was putting it on the trailer)

mark kibort

did the #5-8 bank and all plugs look the same.... except #5... a little wet.
also the compression for all 3 of this bank were also 190psi, but #5 was down to about 182psi......
anyway... doesnt look like any signs of a head gasket issue at all

Lizard928

Fix the damn waterpump before you start it again.
Then test it and see if you still have a problem!
Don't post anything more about theories, torque, HP etc until you have done that!

Imo000

It's wet because the valve cover round gasket is leaking into the spark plug hole.

As Colin wrote, fix the pump and stop using "we" when it's only "you".

hacker-pschorr

mark kibort

bahhhhhh!!

dr bob

So, back to basics. There are two possible causes of overheating. Too much heat going in, not enough heat going out.

Your initial report of coolant missing and no pressure in the system pointed to a leak that prevents the system from staying liquid, and therefore not able to carry enough heat away.

You are going to go after the water pump and related rotating timing-belt pieces for their mechanical issues. That's separate from the overheating unless there's a pump impeller that's spinning on the driveshaft. If the bearings are so severely damaged that the drag is causing the belt to slip, you may be able to find that.

So moving to the other half of the equation: too much heat.

Conditions as I understand them: Ambient 102ºF, track temps probably at least ten degrees higher, based on my memories of racing there in the summer. Hotter in a driving suit. Car has no external oil cooler, uses only the radiator's internal cooler. Radiator is pristine inside (per your statement above). You were using some small amount of coolant in the water, but not enough to raise the boiling point of the mix by more than a few degrees. Are these accurate? Adjust as you see fit and let's move from there.

GregBBRD

Mark:

If you took the time you've spent thinking about and writing theories, you could have had the water pump removed, seen what happened, and had the car back together by now.

GregBBRD

+1

I wouldn't even crank it over to test the compression....

But what do we know?

mark kibort

You have the data correct. yes, on track temps can be near 130 degrees sometimes. this was a hot weekend , but by no stretch, as hot as ive raced there before. the current system has no problem keeping the engine and oil cool on a hot day when properly functioning. however, with suspected air in the system to start..... or the water pump falure, the cooling system was compromised.

i suspect that i had air in the system to start... that started a circulation issue early on that caused more heat to stay in the engine and not get taken away by the water, even though there was water in the system. when pumps fail, the radiator is cool.... radiator being hot is good, it means there is flow and heat is being taken away. but, too low of flow (impeller slip or air in the sytem) causes over teamp.

so the fact remains , 2 quarts were missing upon returning to the paddock, car over heating and no leaks with hoses soft and filled with air. the only logical reason, is that the water was pushed out the overflow and with the cap being a one way valve, and the temp going down substantially on the last 4 laps of near 100mph speed, with fans blazing, the system had lost all the pressure as it cooled.

new water pump on the way as i still heard noises with the stethascope that were much different than a good running 928S4. a whirling noise of the water pump and bearing noise as well as a little metal on metal small chirp at a high frequency. (like when you have put someting on a lathe and you remove the bit, but not all the way, and it catches a small high spot ever revolution..... kind of like the sound when you are machining a rotor and there is one high spot..... might be hitting the block or someting else.

either way, the pump is coming out and we will see if the pump impeller is slipping. (cause of overheating) or if the pump is grinding on the block or if the pump is jammed and the belt is slipping on the water pump.. (unlikely as i think the belt would show some signs of melting or wear and it looks fine)

so.... the wait for the new pump and the investigation and theory validation continues.....................

mark kibort

i know... that's a personal problem... denial.......... i'm working on it!