Please help. Can't fix overheating issue.

[TazMan]

Hello. I'm having a hell of a time with a buddies car that wont stop overheating. I'm not a mechanic, just a parts changer, so I'm hoping some of you more knowledgeable people out there might be able to shed some light on things for me. Let me start from the beggining. It's a 99 Grand AM GT, 130k miles, and a few months ago the LIM gasket started leaking. No coolant in oil or anything. Just some leakage from under the manifold between the heads. He put in a bottle of stop leak and that took care of things for a while. Then a few months later, it started to overheat. Almost no heat at all and the needle would start climbing and the coolant would spray right out the overflow tank hose. The water pump was leaking so I changed that but no help. I changed the cap but that didn't help. I flushed the system as best as I could and burped it but still no help. I even tried running without the t-stat, in case that was getting stuck but it didn't help at all. It just didn't seem to wanna circulate coolant and would just overheating. He put in a bottle of Blue Devil stop leak and that fixed the problem for about 2 days. So, i concluded must be pressure getting in the from one of the cylinders. I took the motor apart, put on another set of heads that i had pressure tested and resurfaced, put it all back together with a new t-stat, and low and behold, the heat worked great and the temp was sitting right around the 200 mark, but, as soon as the needle starts hitting the 200 mark, the coolant starts shooting out of the hose of the recovery tank. I hooked up a garden hose directly to the hose that feeds the radiator from the fill tank, open the radiator drain, and flushed it as best as I could. I've bled the system over and over, tried yet another cap, but still no help. Any ideas what could be causing this? Any ideas would be greatly appreciated and thanks for reading my long post.

[60dgrzbelow0]

TazMan....

This problem often has less to do about water or coolant and more to do about Air. In many modern cooling systems, its possible for large amounts of Air to get trapped in the system in the form or large bubbles or voids that can defy detection and elimination from hosing and other sections within the manifold that are not designed for a fast and efficient flow of coolant. Somewhere on the top of most engines on the radiator or heater hosing arrangements, you will find "Air Bleeder Valves" that will require opening to allow these large bubbles of air to percolate out of the cooling system. When left to their own devices... these air pockets can persistently avoid detection and more or less remain in one area... causing hot spots in the castings that can actually boil the water in some cases into a vapour, risking damage to moving parts nearby by thermal over expansion or even cracking when these dissimilar temperatures rapidly change and defeat the cooling action that would ordinarily happen when the metal is in direct contact with the coolant. I would suggest that you get a container of a gallon or so of 50/50 mix of Anti-Freeze of the approved colour and flavour designated by GM and the rest of Distilled Water...and when the engine is cold ...open the radiator cap an then start the car and watch as the water temp gauge rises to over 160 degrees or so. You should see the fluid in the radiator start to swirl by and this indicates that the thermostat has opened and the water is warm enough to need to be circulated through the engine block and heater and cooled through the radiator. Watch for any bubbling as this is occurring to see if any air bubbles are migrating up and out the top of the opened cap. Next... open the Air Purge Valve(s) and leave them open until you can see a solid stream of coolant pouring out of them...and no staggered bubbling. If the fluid level in the radiator subsides from the loss of the leaking fluid while doing the purge...just keep topping it off until you no longer see bubbles coming from either location. At that point... close the Air Bleed/Purge Valves snugly...top off the radiator and let the car idle in stasis while you observe the water temp gauge rise. If this works and the temps stay nominally in range ...then you have solved the problem. Take the car for a short test drive...while keeping one eye on the road and the other occasionally checking for any spikes in the temps as you go along. If this procedure does not work, please consider looking into the possibility that the radiator thermostat has been installed UPSIDE DOWN. I hope this is helpful to you.

[Azrael]

Try and get the rad fans out of the way and with the engine warming up, see if the entire radiator gets warm at the same time and not just certain parts. There's a chance that running with the stop-leak for so long may have caused a blockage in several rows of the rad. Also, make sure the lower rad hose isn't collapsing anywhere.

[TazMan]

Thanks for the replies. I'll try some of your suggestions but I just wanted to mention, the car isn't overheating and boiling over. It's boiling once the needle hits the half way mark. Once the needle reaches half way, The cap starts to hiss and starts bubbling the coolant out. The temp itself hasn't actually reached any farther then one notch past the half way point on the temp gauge. Again, I'm not a mechanic, but I know at 210 degree's, antifreeze shouldn't be boiling so I'm wondering, where is all that pressure coming from?

[86FieroSEv6]

cracked cylinder wall.

[TazMan]

I was afraid of something like that. I've been bleeding and bleeding but the air never seems to come out. As a matter of fact, it seems to be getting worse. When I pulled the heads, one of the cylinders in the back had a light little rust spot running down it and when I ran my finger across it, it felt pitted a little, but it didn't looked cracked or anything so I just assumed it was worn or something. It just didn't feel completely smooth right where the rust was. Like I said, I'm no mechanic, just a parts changer so I really don't know what I'm looking for in this case. Could that likely have been a crack? How common is something like that in these motors? Also, any idea what I should pay for a decent used block and a transmission? The transmission doesn't slip but doesn't shift great either. Sometimes shudders when changing gears if you really hit the gas hard so if the motors gonna have to be changed, might as well get them both.

[tractorman]

That is a possibility. Remote, but possible.

[Tbay99Venture]

Regarding the one cylinder that is presumed cracked, maybe this is worth a try:

Warm the engine up to the point where the water is gushing and shut it off. Now extract the plug from the suspected cylinder, and good luck not getting burned. I see you say it's one of the cylinders "in the back." Welding gloves may help.

Start the engine and see if the gushing is no longer an issue.

Or maybe that idea is totally cracked!