How is your temp reading...we had a similar problem with my old spec. Dwayne who owns it found that it was not advancing causing combustion at the wrong point.
It gave simptoms similar to what you are saying and it turned out to be a wire near the EGR that was grounding. You might want to drop Dwayne aka xsesiv a note to get the scoop on what it was.
I would first check the timing is advancing as it should as it warms up.

 

I hadn't thought of anything like that. Was there any indication with the sprak plugs? Mine are clean and look normal. I should have put more info in the first post also. It's a used 99 Explorer 5.0 with Mustang EFI and ignition. 40k on the engine. TriStates radiator, 16 lb cap with spring loaded check valve, CSI filler, drilled 180 degree tstat installed correctly. Runs fine, sounds fine. 95c on the highway. No smoke.

 

I would suggest changing your rad cap to higher # at the filler. That is of course if the motor runs fine and what you describe is the only probelm. Retarded timing can cause the problem but I'm sure you've been on that already. See what rad cap # you have and try going one higher ie: from 12 lbs to 14-16lbs. You may even run just a bit cooler with a higher rated cap if pressure is what the motor wants. If you have a 12# cap and the system goes to 13-14psi once in a while....C-Ya . My 351W has a 22 lb on the rad and a 16lb on the filler. With a 12 or even 14lb cap on the filler my motor puked coolant. If your rad cap is already rated high swap it out anyway. Ten bucks. The T-Filler can also be the culprit. Wipe it out good before install and you can even consider the possibility of replacing it because some T-fillers have cheap casting and don't seal right with the cap. What the heck. It's not an expensive experiment !

[ February 06, 2006, 07:33 PM: Message edited by: JAM1775 ]

 

Did you check cylinder pressure? Pull the plug out and screw the gauge in, pump it up with air and see if it holds pressure. This should tell you if you have a leak.

 

the problem we had showed it running hot, the symptoms were very similar, as I recall it turned out the timing was not advancing making the heads run real hot. check to see if the timing is advancing if it isn't call me on 978.887.9104

 

How many cycles have you found the overflow empty? I'm guessing you didn't get a good burp when you refilled from the last blown-off hose and your overflow is going back into the engine replacing the air bubbles.
For now, I'd just make sure I had the correct level in the overflow and run thru enough cycles to see if it finally fills the block completely.
You're not seeing any other symptoms than the overflow emptying. That could be a normal situation if the system isn't yet full.


d

 

It seems to be full. I've filled the blockthrough the coolant temp sensor hole, squeezed the upper hose, left it ovenight, topped it off, etc.. I just don't want to waste more time if it is the head...but obviously I don't want to pull it apart if it's OK. I'm looking for the definitve blown head gasket test!

 

It's not the head gasket! If compression is okay, and the antifreeze test turned a negative result, and you aren't getting any white smoke out of the exhaust when hitting the gas while traveling at highway speed, you can pretty much rule out a blown head gasket. If you want to re-verify, run a leakdown test.

Personally, I would focus on a leak in the overflow tank. Also, keep in mind that when fluid heats up, it expands - and turns into a gas. This is a more likely explanation to your hoses popping off due to pressure rather than a blown head gasket being the source of the pressure in your cooling system.

Good luck finding the bug.

 

How big is your recovery tank?

I have a 13" tube and it is very marginal for size and a serious pain to burp with. Fill it and it wizzes out (edit out pukes), then as the car cools I add more fluid to be sure I don't suck air, then it wizzes (edit out pukes) again. (I ditched puke because it isn't dramatic, just overflows) It actually holds less than a pint, its getting pitched for something a little bigger over the winter.

[ February 07, 2006, 12:47 PM: Message edited by: Narve ]

 

I fought a very similar issue over the last 3 weeks; as soon as I would put my foot in it, the coolant system was pressurizing and blowing all the coolant out of the overflow reservoir. I tried everything under the sun; burping the system some more, different rad cap on the t-filler, everything. Absolutely nothing would fix the problem. Compression check showed 150PSI in all cylinders. All signs pointed to a blown head gasket. So, reluctantly, I torn the engine back down to the short block. Only took two hours. Guess what? Yep, blow-through on #6 (at least) right into a water passage. My critical error was that I reused the stock head bolts and purchased stock head gaskets.

Bite the bullet; you'll never really know for sure unless you pull the heads. It's not a bad teardown.

 

Would a leak down test be absolutely certain? One way or the other?

 

Not for sure. It will eventually as the problem gets worse. We had one that was fine unless it was under full boost. HTH, Cheers Richard.

 

The only thing that is close to certain is a HC test of the coolant while the engine is hot preferrable after it has symptoms of a blown head gasket. Mine was similar to the case richard mentioned in that it was fine, untill I really romped on it.

They really arent that big of a deal to change, takes me about 4 hours total now after all the practice I got doing it a few times.

 

This may or may not apply, but I had a similar problem. I would loose coolant and have to refil from time to time. I did a pressure test and it held pressure fine, so I too was thinking possible head gasket.

I recently did a vacuum test on the cooling system and fould that it was sucking air in through the shaft of the water pump. So it would never pull coolant back from the recovery tank. What it would do is allow air into the system that would expand and push coolant out, just a nasty cycle that was hard to find. It never lost coolant out the pump just air in...wierd.

I just changed the waterpump and the air leak stopped and she pulls the coolant back in from the recovery tank just as it should with no more leak.

 

If it were a head gasket blowing the coolant out, wouldn't the system stay pressurized and the recovery system would not work?

Or is that not true in all cases?

 

Ed-as a dealer tech i'm w/ you on wanting a definative headgskt test.But I've never seen one.The liquid that changes color if exposed to exh gas is definative IF it detects something.But if it doesn't detect anything that is not definative unfortunately.One question that comes to mind reading this thread is the capacity of your overflow tank.Worries me that it is totally empty after cooldown.Just to throw in some numbers for discussion sake, let,s say your engine coolant volume changes by a quart from cold to hot.But your tank holds a pint.You'll never burp all the air out of the system.
Also,checking blowby into the coolant system is marginal.The 125# air pressure is nothing like the actual combustion pressure,so you can pass a leakdown but still have a problem.
Just a few thoughts-best wishes-hope it's not the gskts

 

I had that exact problem. It turned out to be a leaking intake manifold gasket. The vacuum from the pcv was pulling the water in from the front intake manifold water cross-over where it met the head. I figured it out when I pulled the carb, and noticed a green discoloration in the bottom of the intake manifold, and the brown foam on the PCV. Once tha manifold was off, same brown foam on the underside. Drained the oil, water there.

Funny thing was that every pressure test was fine, and compression was good accross the board.

Once I replaced the manifold gaskets (and cleaned the crap out of both mating surfaces), new oil & filter, car now runs perfect.

Ah, those bullet-proof donor motors!