tonyb1968

It figures, I brag about how great my car runs and a new problem shows up.
Car had an intermittent overheating problem that became serious right after I bought it--about three weeks ago. I changed the water pump and thermostat and flushed it out with clear water and the problem was solved or so I thought.
I recently drove the car about 130 miles in one day and it ran beautifully, but yesterday it started overheating again and showed the low coolant light after just a few blocks.
I have searched the forum and found several more things to check out, but nothing exactly like this.
All six cylinders pass a compression check, plugs were normal in color and appearance. No coolant in the oil or vice versa. No steam out of the tail pipe and no coolant leaks. There is almost no way this can be a head gasket.
The system seems to build pressure and blow the coolant out the top of the coolant recovery tank. I replaced the cap and it still happens.
Wife drove the car 2.5 miles to work this morning and it did not overheat, but it did overheat three times ( we NEVER allow the gauge to go above about 75% as this is an aluminum engine and they cannot take the heat). But no problems showed up the day before.
Can't be the weather as I am in Kansas and it is quite cool here this time of year.
So, I have replaced the water pump and thermostat and radiator cap and coolant, flushed the radiator with plain water, and will back flush the heater core this afternoon. The accessory drive belt is new as are the plugs and wires. What else can it be?
I have heard of exhaust pressurizing the cooling system due to a bad head gasket, but wouldn't that cylinder fail the compression check?

R.S.LOGAN

A block test will confirm one way or another whether head gasket is leaking .

chipset

You are describing the typical problems of a blown head gasket but a cracked head
will do the same thing.

tonyb1968

It just seems to me that if it were a block or head, the problem would be consistent. It runs fine one, two, even three days in a row then may heat up once and burp up some coolant then the problem disappears for days again.
I hope it is not a head gasket or head because I am broke and have to turn wrenches myself with the help of my 18 year-old son. Head work has always been tough for me and these DOHC's seem like they will be a nightmare.

R.S.LOGAN

" burp up some coolant " can be caused by head / gasket knackered as it can cause an airlock or pressurise cooling system .

tomw

I, too, would be looking at a cracked head. You can test for combustion gases in the 'degas' bottle with the appropriate machine {I don't have one...} and if there, you have leakage from the combustion chamber to the water jacket area somewhere. Typically, when you get high pressure in the cooling system it is a head gasket or crack.
Other things to consider rule of thumb are that if it gets hot in stop and go traffic, it is likely the pump {or electric fan}, and if it gets hot going down the freeway, its a stopped up radiator.
The computer 'knows' how fast you are going, and is to turn off the fans when velocity is greater than some number {mid 20's or 30's}, but to engage the fans when the A/C is energized. I don't remember all the strategies they used.
A final thing to consider is a sticky thermostat. You might be ahead to get a non-contact thermometer to read the temperature of the hoses, stat housing, radiator tanks, top and bottom, either end, and the return flow to the block. You should get a picture of what is going on if you have access to all that....
tom

tonyb1968

Update:
Refilled radiator several days ago and "low coolant" light has not came back on, coolant "burping" has ceased, has not even begun to overheat again.
I began to notice that it only happened when the heater was on so I turned it off and flushed a lot of plain water thru the system. It was VERY dirty. Coolant is much cleaner now and problem has ended apparently. I still intend to flush the heater core properly and replace the thermostat again just to be on the safe side.
Several guys have recommended drilling a couple of holes in the thermostat to allow some improved circulation. May consider this unless it would be unsafe. Two 1/8 inch holes would allow some circulation to continue while the thermostat is closed, but should still allow for the thermostat to operate properly.
There was no exhaust gas in the coolant recovery tank and everything else checked out. Seems to have been a restricted heater core. Problem has been gone almost since my last post.

Bert

That's good the hear. Thanks for keeping us posted.

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Bert