Hello everyone, my name is David and this is my first post to the forum.

It all started with moments of intermittent over heating then cooling to the point where I started trouble shooting on these forums. I decided to replace the thermostat, top off the coolant and she ran cool and consistently so for a few days. Then it happened. Large puddle of coolant pooled on the road directly below the pressure cap. I poured in some new coolant to see if I could locate the leak and as I poured, it just dumped out the bottom of the radiator at the same seep of my pour. I figured I found the leak. I removed the radiator and saw that all the folded aluminum tabs securing the aluminum section to the plastic were unfolded. It was the original radiator so I figured it was just beat up over time, probably gross inside and the overheating from earlier just did it in. I replaced the radiator. Drove the car for for maybe an hour or so, drove great, temps all fine. Go outside to give it look...big ol puddle of coolant on the street below the pressure cap side. I again poured a little coolant into the radiator to see what was up and yep, poured right out the bottom as fast as I poured it in. Something is generating extreme pressure in there and I can't figure it out. I'd love to be able to fix this without taking it to the mechanic but I'm feeling like this may be out of my depth. any thoughts on what the cause might be?

 

First I would get a radiator pressure tester from the loan-a-tool at the parts store and leak check the system.

But.... What you are describing sounds like the system is over pressurized. I am guessing you have a 3400? If so, this could be a failed head gasket. I dealt with a similar problem in a 1994 Grand Am with the previous generation of that engine, the 3100. What is happening is a battle of which pressure is stronger (the pressure of hot coolant vs the pressure of compression in the cylinders). In my case, the engine ran GREAT without the typical tell-tales of a head gasket (commonly white smoke from the exhaust). As a result, compression gases were forcing into the cooling system via the failure in the head gasket, thus over pressurizing the system and thus coolant pouring out the pressure relief. But, it did eventually blow the gasket between the radiator and the side tank due to the problem with constantly being over pressure. And I did use a pressure tester on the system. Oddly, I was NOT loosing pressure.
I loaned the car to a mechanic friend to diagnose. I believe he said he put the pressure tester on the car to see how fast it built up pressure while idling/running in the driveway. He confirmed it was a head gasket and I went to work and sure enough, he was on the money.

 

Thanks for the reply. Yes it's a 3.4. There are like you said no tell tale signs of a head gasket being blown. No white smoke, the oil is clean and it runs great. I suppose the only way to tell is a mechanic doing some kind of vapor or analysis of gasses? Damn... My brother thought it may be the water pump but it seems to circulate coolant fine even though it's the original pump. Car has only 80k miles on it and certainly sat a while before I acquired it. I may be at the edge off my amateur mechanic skills here. Lol, when your best just isn't good enough :/

 

Do you ever see the temp just start to rise for no reason? If so, I ran into that with the Grand Am issue. I actually pulled over a few times, opened the bleed screw and had straight air come out. And it got to a point you KNEW you had all the air bled out (which means air was introduced and if you are not leaking coolant, only ONE way to get air into it). Towards the end, before I got a diagnosis, it started having a rough idle on start up for a few seconds and then right before my friend got his hands on it, finally white smoke from the exhaust.

I would say if the temp spikes and you can pull over and crack open the bleed screw and air comes out at first and you can repeat this, you probably have a pretty safe bet it's a head gasket.

 

Crazy, I've been chasing my tail with extremely similar symptoms, I changed the thermostat last night and she did fine idling in the driveway, and even under hard acceleration. Once I turned around to come home she started getting hot then randomly cooling again. this morning on the way to work she would get hot sitting at lights but would cool as I pulled away, cruising at 40ish mph she would stay a little on the warm side, and at 70 she was right at 200F. She has puked coolant out of the expansion tank twice now, I was planning on swapping the radiator and water pump but now I'm not sure. this weekend ill be doing sparkplugs, will a compression test should answer this question right?

 

In theory, yes, a compression test should reveal if there is a head gasket issue or not.
Hopefully you can find the root cause. I admit, this is reminds me a bit of what I went through, so I won't be surprised if it is a head gasket.

 

It makes a lot of sense for head gaskets to be the failure point, how else are you gonna get so much air pressure into the cooling system every time the car runs for more than 30 seconds? I skipped the compression test and went straight to taking apart the top end, with how bad my car was getting I'm sure the failure mode will be obvious. I'm doing the ignition system from the coils on anyway, but I'll bet this would solve my cold-start misfire I've been having on cylinder 2.

 

OH, I missed the cold start item! So when I dealt with that head gasket issue, when there no longer was a fight with compression gases, a little coolant got in at least one cylinder. The caused a very brief mis-fire on a cold start (normally done by the time I leave the driveway or first stop sign). I would not mess with coils yet. New plugs and wires, sure not a bad thing while doing head gaskets, coils rarely fail in my experience. I would not touch them unless a problem is proven.

 

I was upgrading to ZZP coils anyway, I rarely do a repair job without replacing most, if not all of a system just because in my experience if I hadn't purchased the coils they would go in 5k miles from now lol. Seems to me like head gaskets on 3.4s tend to fail in their own special way compared to most other cars, glad we've got the symptoms all figured out.

 

I admit, I have yet to use ZZP coils. Everything I am driving is running L67/SuperCharged coils (my 3400 Grand Am and both my L36/non-SC Montes). Because the coils are salvage, I have no idea the mileage. I have dealt with those coils for years (I think GM started using them on the v6 cars in 1993, maybe earlier). Rare a factory one fails and when they did, I was not impressed with aftermarket replacements (they died in like 2 years). I trust salvage coils over part store replacements lol.

Hopefully you find the ZZP coils to be a worth while replacement.

And as for the head gaskets, tells you the gases from compression are stronger than the pressure of the cooling system.