Just wondering if anyone has had symptoms similar to what I am experiencing. The car (97Z) is pushing coolant into the overflow reservoir but only once in a while. The cap has been replaced and tested and the car runs good, no coolant in the oil and fans seem to be operating normally...both come on about when they should. The only thing left that I can think of is the dreaded head gasket but it seems like if it was bad enough to leak compression into the cooling system it would be bad enough to leak coolant into the oil when shut down. Have not done compression test yet (engine still hot as I type) or a leak down test. The car runs cool when driving but does climb when stopped in traffic just as it always has until the fans kick in and they pull it right back down. Guess I just want someone to tell me it isn't a head gasket.

 

Sorry, a head gasket can blow in many different directions. Leaking air or as you said "compression" into the water jacket without leaking water into the oil is very common. The best way to tell is with a leakdown test as you mentioned. The compression test may be a waste of time. The other test that is helpful is pressurizing the coolant system. Had you done any work to the coolant system lately? Maybe trapped air pushing the coolant out? Sorry, best I could to get your hopes up.

 

at my shop we have a suction bottle that you put on the top of your radiator. theres a blue colored chemical in it and if theres exhaust gases present in your radiator/coolant it turns to a yellow/green color. this is how i diagnosed my head gasket problem. (i didnt have any coolant in my oil either)
sry for not so good news hope its not a head gasket.

 

Are you saying that coolant is overflowing out of the reservoir?

Or that coolant is there?

 

It is pushing the coolant into the overflow tank until that eventually overflows.

 

Thanks for the help guys. Gonna do some basic maintenance on the cooling system and maybe a leak down test and see what happens.

 

did you try bleeding the cooling system?? my 97 was doing that also until i took all the coolant out put new stuff in and bleed the system and no problems at all, It also did it when the car was running hot are you over heating??

 

I did bleed the system after adding coolant but it started this problem out of the blue...car had been fine for over 6 months. The car is not overheating, just occassionally seems to get hot enough to push out some coolant even though the guage doesn't show it overheating. I am going to try a few things today like check the temp sensor to see if the fans are coming on early enough and either flush or replace the radiator. I know people will think I am just throwing parts at it but the radiator has been suspect since I bought the car and I plan on keeping the car for a while so I don't mind at all starting with a fresh radiator...plus I found a new one for $120 so i may go that route.

 

In my experience, these radiators plug up easily. When I bought my car it doing same symptoms, so i had the radiator rodded out. that fixed it for about a year, then the problems came back, so I just bought a new radiator, now all cooling probelms gone for over 2 years. Imagine if your radiator was about 2/3 the size it should be, thats about how your symtoms act.

 

That's what I wanted to hear. When I bought the car it was very low on coolant but I never found any leaks and it has bugged me ever since. I could tell from looking into the radiator that it wasn't well maintained but I flushed it and filled it and really haven't had any problems since. I'm now thinking it is the same problem the previous owner had coming back to bite me. So, I'm going to replace the radiator and the engine temp sensor (maybe fans not kicking on early enough and it is cheap) and start fresh and see what happens. I figure even if it turns out to be the worst case head gasket when I get that repaired I definitely want a cooling system that is in top shape. Thanks for the reply...hope you're right

 

speaking from a personal experiance on a truck i had the same thing happen, replaced the cap with a motorad brand or what ever all the chains carry got worse. Finally stopped by a GM dealer and bought a factory cap for about $8 problem solved.

 

Funny you should mention that because the cap was the first thing I went after and it didn't help. I even went as far as testing the new cap and it checked ok. You're the second person that has mentioned using a factory cap. I'm definitely not a fan of chain parts stores except for the basic oil and filter type stuff. Think I might just stop by the local chevy dealer on my way home. Thanks again.

 

Well here's the latest. When I first noticed this problem (pushing coolant into the overflow) I changed the radiator cap and it didn't do again it for a few days. At the same time I changed the cap I also removed and cleaned the throttle body hoping to improve my idle a bit. A few days later it pushed coolant out again and also was idling worse than before...rough but steady...leading me to believe I might have a head gasket problem. I went ahead and replaced the radiator on a Wednesday and was waiting for the weekend to do a leakdown test to verify a headgasket problem. By Saturday, the car had not only given me no more problems with the cooling system but the rough idle had also disappeared so I just left it alone. It is now almost a week later and still running good and no additional cooling problems.

Now for a follow up question. Is it possible that by removing and cleaning a very dirty idle air control valve that I made the idle worse until the valve either seated itself better or the car "learned" the new idle air conditions? I'm thinking that the radiator cured the cooling problem and the idle smoothed out for one of the reasons mentioned above. Any thoughts?

 

My Car Did This Out Of The Blue Also. One Day I Just Parked And I Heard A Rumbling In The Front And Next Thing I Knew I Was Overheating Sometimes And Filling The Car Up With Coolant Until One Day I Bleeded The System (about 1/2 An Hour) And Got All The
Air Out And It Was Good To Go! Hopefully This Is Your Problem Too And Not Anything Worse!