87s4 aut. i have an aluminum radiator reservoir.

each time after several heat cycles this reservoir will eventually go empty. nothing on ground. coolant temps great. needle is at 1/4 to 1/2 mark. infrared is all ok.

before i saw some coolant pooling on top radiator hose connection, i jiggered it a bit and now no leak. i thought that solved it but again reservoir is empty after a period of time.

i am a bit perplexed. anyone have this issue? if so what are most common areas on this car for it to happen?

 

Might be time to buy a cooling system pressure tester..they come in REALLY handy.

You could be losing it...anywhere. Mostly external to the motor..but slowly enough you'll never see it under normal driving as it dries up.

Sitting cold, pump it up..see if it leaks down..my test is taking it to a couple PSI over the cap rated pressure, but not much..and wait to see where it drips.

 

Rent a pressure tester from your local auto parts place. I am coming into possession of a car similar to yours in that the PO threw a new 928Motorsports radiator and aluminum reservoir only to find out he had bad headgasket - save yourself the worry and test it.

 

I had a small leak at the flanges of the water bridge and would notice coolant loss, although not as much as you. I found the leak by first noticing white coolant residue. I would also check very carefully the heater hose area and block off plates. Seems like you would have a noticeable leak with that much coolant being lost... but maybe most of it is evaporating at the leak.

 

Follow Jeff & Kevin's advice re: the coolant system pressure tester. Most parts places will rent one to you at no net cost. You pay when you get it, refunded when you return it.

Many small cooling system leaks show up more easily when the engine is cold. Some small leaks let coolant evaporate before you see any liquid. I use the Zerex G-05 coolant that's a really pale yellow at best, so it's togh to spot leaks until you start to see the deposits left after it evaporates. Anyway, cold pressure up to about 13-14 PSI will do the job. The cap should relieve a little north of 14 PSIG, at one atmosphere. Anyway, pump it up cold and let it sit. Pressure will drop if you have a leak. Let the car sit pressurized cold overnight. If there are external leaks, you'll see them.

Head gasket leaks may go into a cylinder, or into the oil system. If the oil has coolant in it, it will be a frothy brown milkshake after the engine is run. Sitting, the coolant will sit under the oil and so be detectable by pulling the drain plug a little. Coolant will come out, then oil. Coolant into a cylinder will "steam clean" the spark plug in that cylinder, leaving it almost white. If your block pressure drops overnight but you don't see an external leak, pull the plugs and look in each cylinder with a flashlight (borescope is better if you have one...). Spin the engine a few cycles on the starter before you put plugs back in, and watch for coolant ejecting from the plug holes. Might not be a bad time to test/verify compression in all cylinders.

Coolant doesn't just disappear; it goes somewhere, and it's almost always somewhere that isn't good. With luck it's an easy hose connection. Less luck it's the %$#*!! hose under the reservoir, a heater hose or the steel tube that connects those pieces. The little stub hose between the head and the heater control vlve is a notorius failure point. Then radiator end tanks. As Don mentions, there are seals/gaskets at the water bridge and the thermostat housing. There's a gasket and seal at the water pump too, plus a bolt or two on the tensioner that may back into the water jacket. The heater core in the dash. Lots of places to look.

 

all hoses are new when i did the engine refresh etc. including all hoses underneath reservoir, all heater hoses, etc etc.

some points:

--there is no mixing of oil and coolant. i just did an engine oil change and oil was good.

--coolant color is clear green, no murkiness.

--i have noticed that the 928s4 coolant hoses especially upper and lower are very large and the clamps dont stay where they should be and loosen over time. i put loctite on some clamps. i sometimes see some coolant wetness below lower radiator hose clamp....before i did tighten the temp sensor on bottom front left of radiator....

--i have not used that pressure tester in the past.

--i do hear an audible slight hiss when i loosen the reservoir cap so there is some pressure there after engine cools down.

i will continue to troubleshoot....

 

One of the classic spots for leaks is around the top of the passenger-side radiator tank. The coolant evaporates quickly off the hot surface and you have to look closely to see the white dusting where the leak is happening.

 

yes that top side passenger side hose clamp is wedged in next to the shroud and the clamp was a bit askew.

it was leaking there in past as i could see some green on the rad top.

i rejiggered it and now i think it doesnt leak....but again it might have evaporated...

but yes that area was leak prone....

 

If you BUY a tester, you'll never need to use it.

That's how the world works sometimes.

 

If you RENT the tester for FREE as described above, and USE IT ON YOUR CAR, it will tell you a whole lot in a short time about where it's leaking. Or you can dink around, and hope the dinking solves the problem.

Post back after you've used the tester.

 

But if you BUY it, the gods make sure you wasted your money.

Guaranteed leak free, forevahhhh!