This will seperate the men from the boys!

[asbennett]

Hi - I have a 2000 Olds Alero 3.4L V6. The coolant is building up pressure and pushing coolant out the overflow tube. I also noticed the LIM gasket was leaking.

I replaced the LIM gasket. This fixed my leak. But still pushing coolant out the overflow. I replaced the water pump, the thermostat (195 Deg.), the coolant pressure cap (15psi), I had the system flushed and replaced the coolant with the Green antifreeze. I made sure the air was removed by bleeding it througth the bleeder valve port. I also replaced the drive belt to make sure it was not slipping on the water pump pulley. All of this still did not fix the overflow problem. I do not know what else to check.

I also loose my heat when driving. It comes and goes. I assume that this is due to the coolant lose. Also, when I loose the heat the temp shoots up really fast.

What else is there that can cause this to push coolant out?

[BNaylor]

That doesn't sound good. It looks like you have replaced all the typical items that could cause the problem. I would run a cooling system pressure and leak down test. The goal is checking to see if you have a bad head gasket. Some sort of excess pressure is causing the system to exceed the 15 psi rating of the cap causing the coolant to dump. Another suggestion is to remove the spark plugs and look for possible coolant in the cylinders.

[asbennett]

I repalced the plugs when I had the intake off and everything look good. Also, no indication of water in the oil. What could be building up pressure other than heat? And if it is heat, why is the temp gauge reading normal?

[BNaylor]

Originally Posted by asbennett

I repalced the plugs when I had the intake off and everything look good. Also, no indication of water in the oil. What could be building up pressure other than heat? And if it is heat, why is the temp gauge reading normal?

I thought you said when you were losing heat the temperature gauge reading was shooting up? It is a weird design on the cooling system and having the reservoir pressurized but it must be something but your guess is as good as mine. Clogged radiator? and are you sure the thermostat is working properly?

[pistonring]

My guess is a bad head gasket, bad head, etc. Probably gasket. When a head gasket blows between the chamber and a coolant passage, part of the compression goes into the coolant system, thus air. When this pocket builds enough, it purges to the overflow reservoir, usually blowing through the heater core, thus temporary heat loss. This just happened to me on a 3.8 tbird. Strange how the temp gauge would fluctuate and when it dropped the temp from the heater dropped with it. It was the air getting into the system. Good Luck, but no good news here.

[xeroinfinity]

If that thermostats in backwards it'll effect the flow.

But I'd say your head gasket is bad causing the overflo.

But when you say your heat comes and goes that's due to air in the cooling system.
I'd try purging the air out again.
This too can cause it to over flow.

Went though a simular thing on my 99 SE, after replacing the LIM 4x in one week, I pulled the heads gaskets were shot !

Also as Bob recommended check your plug again.
If any have a white blisterd electrode then you have coolant leaking into the cylinder(s).

Good Luck

[asbennett]

If the head gasket is leaking and causing excessive pressure to build up in the cooling system, would I be able to detect this by seeing water in the oil? How can I test the head gaskets to be sure this is the problem before paying to have them replaced?

[pistonring]

Not necessarily, the gasket has a hole in it for each of the cylinders, holes for the oil and holes for the coolant. Usually, head gaskets blow between cylinders or between the cylinder and a oil or coolant passage. It is very common to have one blow from the cylinder to a coolant passage. A lot of time, the gasket is just weak and can not contain the cylinder pressure but can contain the coolant pressure, thus air will move to the coolant system but not vise versa. You may not lose any coolant at all. But when pressure moves to the coolant system, it has to go somewhere. Sometimes you can fill your overflow reservoir and watch as bubbles continue to eminate from the coolant. Sometimes it is so bad it just blows the coolant out fast.

Good luck with diagnosing yours.

[Shoerfast]

Originally Posted by asbennett

If the head gasket is leaking and causing excessive pressure to build up in the cooling system, would I be able to detect this by seeing water in the oil? How can I test the head gaskets to be sure this is the problem before paying to have them replaced?

There is a simple reason that combustion gas can flow into the water @ 150 PSI + and coolant at 15 PSI wont flow the other way. The high pressure and thinner A/F mixture will out maneuver coolant. When the engine is shut-down, steam dose not always discolor plugs and the combustion chamber as the head-gsk may hold at 15 psi to prevent reverse flow.

The reason coolant doesn't usually get into the oil is that head-gsk's / cylinder - head design bring the water jackets closer to the combustion chamber then the oil passages. (Sometimes warped heads will put a lot of coolant into the oil.)

Usually an engine that is "passing gas" into the coolant has a distinct smell in the overflow (recovery / puke) tank, and discolors the tank. Another test is to top the coolant off (t-stat out) purge the air and rev the engine or put it under a load and watch or bubbles at the radiator cap, repeating the test if bubbles are noted by shorting cylinders can give you the exact cylinder, a moot test as your going to repair everything anyway.

[BNaylor]

Originally Posted by Shoerfast

Usually an engine that is "passing gas" into the coolant has a distinct smell in the overflow (recovery / puke) tank, and discolors the tank. Another test is to top the coolant off (t-stat out) purge the air and rev the engine or put it under a load and watch or bubbles at the radiator cap, repeating the test if bubbles are noted by shorting cylinders can give you the exact cylinder, a moot test as your going to repair everything anyway.

Good explanation. Actually the way the cooling system is designed on GM "N" body cars with the 3400 engine I don't think that part highlighted is necessary. The cooling system reservoir is pressurized and the radiator itself has no cap. The pressurized cap is on the reservoir. In most cases with a bad head gasket you will see that anyways or see coolant blowing out the overflow.

I vote headgaskets.