Very Odd and Frustrating Overheating Problem

Hi I'm new to this forum. I have tried to research this problem but so far I haven't found an answer, so I'm hoping one of you can help. I have a 1990 Sub. Legacy, 2.2 automatic all wheel drive. It is leaking water somewhere but I can't figure out where. I fill the radiator, then run the car with the heater on until it warms. Then I remove the bleeder plug and fill it the rest of the way. It will run at normal temp. for several days and then start to overheat. I then add more water, burp it as before and it will run at normal again for several days. Over time I must have added gallons of water but I never see any leak. I put a can of Bars Leak in but that hasn't helped either.

 

At first I thought it was a head gasket, but there is no smoke and I ran a radiator gas test twice with negative results. Also, there is no oil in the water or water in the oil. I have listened for a hiss and watched for steam or discoloration but I can't see or hear anything that would indicate a leak.

 

I have noticed that the overflow tank will fill completely and does not seem to empty back into the main radiator as the car cools. I suspect that there may be a very small leak somewhere that is big enough to leak air into the system so that the over flow tank won't siphon back into the radiator but I can't find anything. If it isn't siphoning back into the radiator that would explain how the radiator is losing water gradually but it doesn't help me find the leak.

 

Does anyone have any ideas? I'm stumped. Thanks, JH

Have you gotten under the car and looked for signs of coolant leaking? If it does not drip on the ground, leaking coolant can leave stains (residue) where it leaks out.

if you see nothing, then i suggest you pick up one of these [ame=http://www.amazon.com/Lisle-24610-Spill-Free-Funnel/dp/B001A4EAV0/ref=pd_sim_auto_10?ie=UTF8&refRID=1W8TCKKFXV4ABXXCJG0B]Amazon.com: Lisle 24610 Spill-Free Funnel: Automotive[/ame]

You attach it to where the radiator cap goes, keep is slightly filled with coolant and run the car with the heater on. (there are some videos on youtube describing how to burp air bubbles from the cooling system) The point is to rev up the engine moderately (2-3000 rpms) and once it gets warm you just keep looking for possible air bubbles to emerge... It is ABSOLUTELY possible to have a bad head gasket that draws in coolant, but passes ALL other tests. This sounds like your situation.

Hello;

First of all never use stop leak, especially Bars. You have a head gasket going bad, the compression is pushing out the coolant, via the overflow bottle. You will need to check the flatness of the heads and block before replacing the gaskets. In my case the decks were warped .005 inch, and the heads were flat. Steven.

Thanks for the input guys. I suspected a blown head gasket but can I have a blown head gasket and still pass the radiator gas test? There aren't any other symptoms either, no oil in the water, water in the oil, smoke on startup, fouled plugs . ..

 

If it is the head, I assume I have to tear down the whole motor to have the top of the cylinders leveled. Am I correct? Can both heads be removed with the motor in the car?

 

Thanks, JH

No, you'll need to pull the engine to get the heads out. Err, well, it can be done in the car, but, since it's likely you'll need to deck the block AND the heads, you'll want to tear the whole thing out.

I would get the heads decked for sure but getting the block decked is often not necessary. To get the block decked it would have to be split and the internals removed.

 

Sure you can do it with the engine in the bay but it is a pain in the ass. If you pull the whole engine it will make your life so much easier, plus while it is out you can replace all the seals and replace the timing belt, idlers, pulleys, etc. I know a lot of dealerships replace the heads without pulling the engine though.

I would get the heads decked for sure but getting the block decked is often not necessary. To get the block decked it would have to be split and the internals removed.

 

Sure you can do it with the engine in the bay but it is a pain in the ass. If you pull the whole engine it will make your life so much easier, plus while it is out you can replace all the seals and replace the timing belt, idlers, pulleys, etc. I know a lot of dealerships replace the heads without pulling the engine though.

 

No, block decking is rarely necessary; only in extreme warpage due to neglect or abuse.

 

People act like pulling the engine is super-complicated; honestly, it's not that bad. Is it quick? Absolutely not. Is it effective? You betcha!

 

I'll never understand how dealerships perform the work they do. It's no wonder they often produce shoddy results and unhappy customers.

Hello;

When this happened to me, I took a piece of heavy C-Iron and milled one side flat. Basically a giant sanding block, and kept changing to a finer grit of until the finish was where I wanted it. You are dealing with an aluminum block and the decks can move a bit along with the heads. The gasket combustion sealing ring acts like a reed, letting pressure out but preventing the coolant rushing into the cylinder. The reason for a complete inspection, do the job once! I simply plugged all holes with paper/plastic and vacuumed/wiped out the dust that was created. Been rebuilding heads/blocks for years and you would not believe the amount of flaws that have been revealed, Steven.

Silly question but have you checked if the heater core is leaking? Is the floor wells wet?

Do you have access to a coolant system pressure test equipment? Test the radiator cap also.

In case this helps I posted the FSM procedure for replacing the headgaskets here: http://legacygt.com/forums/showthread.php/blown-head-gasketi-186097.html

 

I also posted a link showing how to replace the heads with the engine in the car. In fact mnstrmech has replaced heads with the engine in the bay and he said it was a piece of cake but he is also a talented mechanic.

I have done heads in the car. I did not think it was that difficult.

Was an L series turbo wagon.

I am an ex mechanic.

If it comes down to taking the heads off get them tested for cracks also.

Thanks for the links. There's no water on the floor boards so I don't think I

have a leaky heater core. I don't have a radiator pressure tester, but I've replaced the cap twice. I'm going to run a compression and leak down test as soon as I get a chance. That should give me a better idea of what's going on. I'll post the results, but it may be after thanksgiving.

Again, thanks for all the help.

Okay, it's been a while, I haven't had time to test the car until now what with Xmas and all. So, this is the situation: The car over heats after just a few days of running. When I add water the radiator is low but the over flow is full of water to the top. I've looked for leaks everywhere including the heater core but I can find nothing. I figured it must be a head gasket so I did a radiator hydrocarbon test 3 different times by 3 different people will negative results. I checked for water in the radiator or in the oil - nothing. No sign of water in the tail pipe. No smoke on start up. I did a compression test and all of the cylinders are within spec with no sign of a compression leak. I was going to do a leak-down test but since it passed the compression test I didn't bother. I've replaced the radiator cap several times and I'm sure the cap is not leaking.

So, I'm baffled. It doesn't seem to be a blown head gasket unless that can happen with absolutely NO symptoms other than coolant loss. The only thing that makes sense to me is that there must be a pin hole some where. Small enough to not let water leak out but large enough to suck air back into the system when it cools. That would cause the system to pump water into the over flow when hot but not siphon it back as it cooled. But I can't find anything.

I don't want to go to the trouble and expense of replacing the head gaskets unless I'm certain that is the problem. Does anyone have any suggestions? Thanks, Jim

Smell the coolant and the overflow. Check to see if the tank is discolored black. We do them in car all the time. Its a rarity they require any machining unless severely overheated.

Hello;

You should have done the leak down test! A small compression leak will pressurize the cooling system and cause the coolant to exit the over flow bottle. Subie's are reverse flow, so the top hose is the pickup and the bottom is the return. When the coolant level drops below the upper hose, the car overheats! I deal with bad head gaskets/cracked heads frequently, Steven.