How can this be without boiling over? I can run for 30 minutes, and unscrew the cap on the reservoir and NADA? I would expect at least a little burp, something? Compounding further, I think I may have a VERY SLOW head gasket leak, because I SLOWLY go through coolant, (Maybe a cup in 200 miles) and my number 2 plug looks a little funky.
https://www.f150online.com/forums/v8...gs-please.html

But how in the heck can it come completely come up to temp, and not boil over if there is a leak somewhere?

I still have 3 weeks of warranty left, and I want all my ducks in a row. Not sure if the warranty is any good though......

 

Sounds like you answered your own question, if you have a leak, you wont have any pressure build-up in the system. Unless it goes over 212*+ it won't boil over anyway. A cup in 200 miles is not a very slow leak. Have the system pressure tested and I'm sure you will see what is going on.

 

You probably have a funky thermostat or the seal at the cap, after the pressure test replace it.

 

Nope, no pressure there. Since the cap is forever venting.

 

I guess autozone loans out the pressure tester, I will have to try that.
I suspect the cap as well as a possible gasket. I did drive it 1500 miles nonstop with no issue a couple weeks ago.
Just changed the coolant a few days ago, and have had to add water a couple times to bring it up to the upper index mark on the bottle. I know some of that may be bubbles settling out after the coolant flush.
Will have to wait until next week for the pressure test though. It scares me because I know how sensitive and hard to get to the heater core(s) are. So 15 pounds for the pressure test?

 

But if you are on a 45 minute trip, and the pressure cap is bad, wouldn't it boil over?

 

Yea, you need to specify whether you have a 2 valve or 3 valve engine. They had both for that model, and model-year. I believe you have the 2 valve correct? So if you could perhaps add that to your info, -top right corner (best place), that would be great. Plus you will get the correct and specific information as the two engines differ quite a bit.

 

Not if the coolant stays below 212 F.

You need to get a hydrocarbon test done on the coolant.

 

Looks like yer gonna find out if that warranty is any good. Unfortunately some of the car sellers will screw up the coolant cap so the system doesn't build pressure and push coolant out of a bad head gasket. I'd get a new cap today and expect it blow coolant out the tailpipe. Then you'll know if the warranty is any good....which I doubt. Might start looking for another vehicle or a new engine. Neither one is going to be a cheap date considering how much yer already out.

 

Yep - screw up the cap and put a 180 thermostat in, and nobody will be any wiser.

 

I have too much invested in this thing to push the eject button. It is a beautiful clean XP, which I now have (including the tax I just paid to register it) 13K into. Brand new tires, stereo, seat heat, yada yada.
I bought it from a place called Donovan Buick out in Wichita, and drove it home to upstate NY. They claim it has a 60 day warranty on it, backed by GM. Who knows. First Ford dealer I called said it would be about $2500, to fix one head gasket.
I will be out of town rest of the week, so I guess I will have to continue the fight next week.
First order of business is to pressure test the system I guess.

Anyone know how a 60 Day used car GMPP warranty works? I can find nada about it on the net.

 

I would start the procedure at your GM store now. I would leave out the I did this and I did that information, asking them to fix the water leak please. Once they start fixing the water leak you will get fixed I believe.

 

Maybe much adieu over 'nutin.

So I got the pressure tester from Pep Boys (about $200 deposit, you get it all back) and the first thing I tested was the cap. It would hold about a pound.

It (the pressure tester) is on the cooling system now, and has not budged in the couple minutes so far. Pretty stoked. I'll throw the new cap on there (tested and passed!) and drive around and see whats happening. Funny, I never smelled antifreeze. Or saw steam for that matter.

Nice day maybe after all.

 

Great! - So your @ 15 or 16 psi then? For a minute there, it was sounding like you had a 6.0 problem. Many Cap/Degas problems with those. That's what your problem reminds of anyway. There's a bunch of Ford TSB's about that, -if you have access.

 

Without the pressure cap functioning you would gradually loose coolant. Boil point is much lower with only 1 PSI cap. Believe it, the motor creates steam as it runs and a higher PSI CAP ^ raises the boiling point by 10's + 10's of degrees holding the coolant in the radiator and tank for needed reuse. Sometimes a poor cap, when left that way, over time can/will create all kinds of internal problems, usually rust and gasket related.