Well many of you know, several months back, we overheated the Trooper and cracked the factory head, as many of us 2.6L owners do. We replaced it with a brand new AMC aluminum casting that has been working great since then.

However, just a few weeks ago, we noticed some symptoms begining to reappear... such as the surging at idle, etc. So we checked the radiator and found it had puked out over half its contents into the overflow container and the engine compartment.

So the troubleshooting began....
- we boiled the thermostat to make sure its opening. And I can tell it is by the upper radiator hose getting hot too.
- did a complete flush and fill on the coolant system. using the garden hose to completely flush out the radiator, the block, and heater core. no signs of blockage from any of those systems
- and finally, replaced the radiator cap with a brand new one
- oh and I should say, the temperature guage doesn't report anything abnormal while running the vehicle, if anything, I think it tends to read a little cooler than it should once warmed up.

Even with all that, after about 10-15 minutes of driving, it will gradually transfer the contents of the radiator to the overflow container. such that in about 10mins, the overflow will rise from the min to the max line.

Can anybody offer some words of encouragement? Where we should go next in our troubleshooting process? pressure test? dye? replace water pump (though its not weeping)?

-Rob

Does the temp rise from just sitting there or only while your driving? I think the water pump is a wasted effort, unless you think that the impeller blades are damaged or some how gunkified to the point that it isn't pumping.
Did you burp the system of air?


Madcat <img src="/forums/images/graemlins/kewl.gif" alt="" />

Sounds like the coolant is being pressurized somehow. Leaking head gasket or cracked head would be my guess. I hope I'm wrong. <img src="/forums/images/graemlins/frown.gif" alt="" />

DITTO


Madcat <img src="/forums/images/graemlins/kewl.gif" alt="" />

I'll vote like Dave. <img src="/forums/images/graemlins/smile.gif" alt="" />

Michael

pressurized? isn't the cooling system normally under pressure? or is that a typo?

I thought cooling systems are normally under pressure to raise the boiling point of the coolant? or are you saying I've got a leak somewhere and loosing that pressure, therefor I'm boiling water sooner than I should?

Thanks guys
-Rob

I don't disagree with the notion that the system could pressurize from a bad head/gasket, but the second part of your post (after all the work you did) you say the coolant level rises in the overflow from minimum to maximum after ten minutes of driving. Does it stop there or will another ten minutes of driving see you leaving a trail of green down the highway? The overflow is just a mini expansion tank that makes room for the heated water. I would expect the level to rise.

My own experience is if the engine temp reads low it doesn't necessarily mean the engine's running cool. It might mean the probe isn't covered with coolant. I managed to melt a valve seat into the head running an engine that was abnormally cool after a head gasket replacement. I thought it was great, running cool, until I lost compression in that cylinder.

Come to find that unless you make sure all the air is out of the galleries of the head when you fill the engine, you are pretty much putting a cork in your coolant circulation system. Some coolant will get through but not enough flow to cool the engine. The block can take the heat, but that soft aluminum head will take a beating with overheating. A lot of posts have said park on a slope with the radiator cap out and run the engine to burp the air out. I prefer to unscrew the air bypass valve from the top of the thermostat housing and fill the radiator until coolant flows out the top of the thermostat housing. Here's hoping it was just a bad radiator cap that caused your problems<img src="/forums/images/graemlins/cheers.gif" alt="" />.

Sure, your coolant is normally under pressure from heat expansion.....but not from engine compression leaking into the coolant passages. There are normally two places the combustion chamber/cylinder can leak.....around the head gasket, or through a crack in the head itself. If that happens...something's gotta give. Either the coolant will be pushed out the radiator cap and into the overflow, or it will pop out a freeze plug. Other things can happen, but that's the most common things I have seen.

what would you recommend to confirm this?

cylinder leak down test?
cooling system pressure test?
florescent dye in the system?

-Rob

I'm pretty sure I can rule out air at this point. We've done several test runs, all with the same net result... and topped off and aggressively bleed the system between each run. Even flushed, filled, and bleed the entire system between runs with the same behavior.

now, I'm either really bad at this whole bleeding concept, or something else is afoot. and like I mentioned, this didn't start as a result of messing with the system. It started on its own after at least a month or two of solid running.

Thanks
-Rob