shiners780

A few weeks ago I started a thread about a possible headgasket breach. I found some coolant leaks and it was determined by general consensus that possibly the leaks and resultant air pockets was causing the coolant to overflow.

I fixed a hose leak, which was a major contributor to the coolant loss as determined by using a coolant pressure tester.

A second leak seems to be from the waterpump gasket. However at 14psi it only leaks about one drip per two minutes. Not a very big leak at all.

The final leak was from the radiator. At 14psi it drips about once per five seconds. I just took the radiator out and had it tested at a shop. The leak is from a rubber gasket along a seam, which they were not able to satisfactorily repair, so I'll need a new radiator. The radiator flowed "average", not great but not drastically stopped up either.

At my last track event, I lost about 1.5 gallons of coolant over a period of approximately 5 hours on track. I kept topping it off between runs. My question is could a drip every five seconds from the radiator add up to 1.5 gallons over 5 hours at operating temperature? Or is the coolant disappearing from somewhere else?

Final question - if your car has been sitting for a week and you remove the expansion tank cap, is there a little pressure that escapes upon removal of the cap and some burbling from the coolant in the tank? I don't recall that happening in the past, seems like there was no residual pressure.

I'm still trying to rule out a headgasket issue.

Thanks in advance!

tyro

Have you rigged up a catch can of sorts to the coolant overflow line?

I'm sure you've seen the posts- drive the car hard, get coolant out the overflow.

I had this same situation after tracking the car. Head gasket. There was a nice path of carbon from the cylinder straight to the water jacket in the head.

M758

I would replace the radiator first. You could still have other issues, but you will be hard pressed to find them with a leaking radiator.

M758

The 944 or 951 should rarely ever spit water over board. Doing so is a sign that you have problem. My 944 race car gets driven very hard and I never fill the water during a weekend. I do check and top off the oil, but my cooling system is solid. I have the stock overflow hose rigged to dump in to a catch can, but I have never had and fuild in there.

shiners780

I do think the coolant has been puking out the overflow hose on the expansion tank. I hadn't put a catchcan on the hose, but a couple times after coming off the track I noticed a few drops of coolant drip off the bottom of the car on the driver's side. I don't think the radiator leak would produce enough coolant to collect on and drip off the bottom of the car.

I think that is what Jess was saying, that coolant being forced out the overflow is an indication of a problem and not normal.

So am I understanding this correctly, that if the headgasket is going that under compression air could be forced through the headgasket and into the cooling system, which in turn would force coolant out the overflow hose?

I guess I'm searching for any other possible explanations before tackling a headgasket replacement.

tyro

Correct. Cylinder pressure>cooling system pressure.

I finally stopped thinking that I had air in the system/leaks/etc., manned up and did the headgasket after I found coolant in my catch bottle.

So..do the catch can test and let us know.

goldminer

I had a similar issue with my car. Coolant would "vanish" even though the car never got hot and there were no signs of a leak. Eventually I blew a heater hose on a track day. When the workshop left the cooling system under pressure overnight after replacing the hose they found a puddle under the car. Turns out the radiator had a small leak.
What I think was happening is that I was losing coolant as steam through the radiator leak and that's why I couldn't find the problem.

lleroyb

You might try pulling the plugs to see if one of pistons is being steam cleaned.

Lou

shiners780

Did that, all the plugs looked exactly the same. I looked through the spark plug holes with a flashlight and they all looked the same down there as well. No oil in coolant or coolant in oil.

Compression numbers on a cold engine with a teaspoon of oil in each cylinder were:
1-138
2-141
3-154
4-149

Lots of air getting into the cooling system. I continuously bled air out the bleeder bolt. Temperature on track was fine, fans work fine. Coolant level would be down in the reservoir after a run, I would crack open the expansion tank cap after the car cooled down a bit and lots of pressure would come out and the coolant would burble back up into the tank. Then after the car cooled some more the coolant level would be down from it's original level.

KuHL 951

I know this sounds too simple but I have solved more coolant problems on numerous cars with a new tank cap than I can count. If the system doesn't hold pressure it will puke an overflow every time.

shiners780

I tested my old cap and it didn't hold pressure....at all. I did replace it with a brand new Behr cap and the coolant issues didn't go away. I love simple solutions, unfortunately this one didn't work...thanks though!

KuHL 951

Sorry, I always go for the simple cure first...it must be your seat belts are too tight
Sounds like you have a HG issue actually. Billthe3 had a similar problem that was confirmed by a compression test while hot...N0.1 was down about 30psi compared to the average. Strange thing is the car ran OK even with the HG problem except for the adding coolant every 3 days.

shiners780

Exactly! The car runs great. No smoke, runs cool, full boost, etc. Weird.

special tool

Use the cometic stainless if you do.
This is one of the best products available for the 944 - I can't say enough good about them
You would not believe what I have put mine through.

KuHL 951

Yes we do... you are a brutal abuser of the 2.5L...you should be proud and ashamed at the same time