Sounds like a miss on cold starts, and vanishing coolant.

I think you figured it out. Sounds as though you have a bad gasket -- intake, exhaust, or most likely a head gasket. The gasket likely has a crack in it -- the crack is allowing air to be sucked into the cylinders, thereby making the air-fuel mixture more lean than it should be and this is causing the engine to run rough. When the engine gets warm, the gasket expands and seals itself, thus, the engine runs normally when warm.

The disappearing coolant is the result of coolant running out through the crack in the gasket. It may be that coolant is being pulled into one or more cylinders where the heat of combustion turns it to steam and it goes out the exhaust -- or -- the coolant may be blowing out through the crack in the gasket -- or both.

Of course, this diagnosis is not definitive -- just the opinion of an old shade-tree mechanic.

really...?? Please tell where you are employed!

I think at minimum, you need a new radiator cap.

Dave

Your diagnosis sounds good to me but what if it runs rough at start-up but is not losing coolant? I have a '92 Explorer 4.0 V6 OHV with a mere 275,000 miles on it and it runs rough at first then smooths out after a minute or two (or if I rev it up a little at first). I also have not pulled the plugs recently but could leaking valve seals cause this? I recently replaced the radiator because it was dumping coolant out of the reservoir and it had white smoke coming out the tailpipe (burning coolant?). I added some (GASP!) stop leak that is supposed to seal cracked heads and leaky head gaskets and the smoke went away but it still runs rought at startup. I also recently replaced the water pump and have cleaned the MAF and the other (?) sensors. The intake manifold gaskets have also been changed. I realize at this many miles it could be more than one problem. Could a clogged radiator also cause pressure build-up and coolant loss and contribute to a head gasket leak?

Ulysses, Your problem sounds IDENTICAL to mine. If your truck has 275,000 on it, I would say its due for head gaskets anyway. If you know you can do it yourself, it will probably only cost you about 150 bucks to do it. I get a discount at O'reillys becuase I am an automotive student, so its only going to cost me about 100 bucks. One of the primary reasons on my truck I think that its the headgasket is due to the fact that when I turn the truck off it still pushes air out of my radiator into the expansion (overflow) tank. If yours does this, and when you open the radiator on a cold engine first thing in the morning, and you get pressure out of it.. You probably have a leaking head gasket... Leaking Valve seals usually dont cause rough starts unless its allowed to go on too long and the plugs are indeed fouled. That is the second symptom of leaking valve seals. But the first symptom of leaking valve seals, is blue smoke when you first start the engine. Thats cause its burning the oil that dripped into the engine when it wasnt running. Just watch your tail pipe when first start your car (should be easier to see on a warm engine). So the next time you take it to the grocery store and turn it off for like an hour and then restart it.. If your valve seals are leaking, this is when you will really notice it.

I've looked at the situation and have been putting it off mainly because it looks like the exhaust manifolds are going to be a nightmare to remove. At the moment the engine runs amazing well for the number of miles on it and easily passes the California smog tests.

Thanks for the info. This narrows it down as I'm no longer getting smoke on startup and it was white, not blue. If the stop-leak did what it said it would do then by temporarily sealing the head leaks that would indicate to me that they are indeed leaking.

I've read several claims of 350,000 miles on this particular engine in the Explorer and most of those folks were still driving them so based upon that I think it would be worth the trouble to replace the head gaskets and get my (last?) 75,000 miles out of it.

I get a

Ok here is the skinny guys. I JUST got done doing a head gasket replacement on my truck. The short of it is, that either the intake gasket, or the the head gasket was at fault and it has stopped its problem.. Everything works as its supposed to. I do think that it was the head gasket. The reason I think this is because there is a spot on one of the gaskets where you can see a deterioration of the gasket material in between the water jacket holed, just outside the fire ring on the #5 cylinder, which also happens to be the cylinder that when I unplug the spark plug, it doesnt change the sound of the engine on the cold start.

For the person that said that I needed a new radiator cap, at mininum. I had it checked yesterday, and it is fine. It is rated at 15psi and it is releasing at 14.7psi, and thats good enough for me.

Thanks for all the replies guys, and I will try to offer insite where ever I can. I am not going to lie, if I am not there to diagnose the problem, then there is a good chance that I could be wrong, but it doesnt hurt to put out my thoughts and have some folks respond to them..

Thanks for following up and posting your results! I'm glad you got your problem fixed.