Latest (and probably final) update:

The first time I drove the truck after thinking I had it fixed this morning, some water was forced out of the overflow reservoir cap after about 15 minutes on the road. So I started watching the temperature gauge very closely, and sure enough it started climbing again. The needle went back down to its normal position without hitting the red zone, but this made me think:

If the cap has failed and can no longer hold enough pressure then of course the engine will force coolant out of it -- which means air will replace that coolant, and then that air will cause the other problems I've been seeing.

I was near O'Reilly Auto Parts at the time, so I stopped and bought a new coolant cap for $7 and installed it immediately. From then on, and all the rest of today (we were on the road for several hours today) no coolant has been lost, and the temperature gauge needle hasn't budged from its normal operating position.

So finally, I think I have my cooling system fixed!

 

No, the engine wont force coolant out of reservoir without a cap. It can run without cap just dandy. You will just have evaporative losses.
When you remove cap suddenly on pressurized system, the vapor space expands and rushes out the opening, entraining liquid with it potentially on normal old fashioned liquid full radiators with cap on top.

On our trucks with vapor space at top of radiator, equalized to reservoir, this doesnt happen really. You can remove your cap slowly while hot and running.

if your liquid expands and discharges when take the cap off reservoir, its because pressurized gas is in the liquid circulation somewhere it should not be.

Long story short.....the overheating also has zero to do with a leaking cap. Air cannot be entrained into circulation from the reservoir, its out of the coolant circulation.

Id still worry you have a blown head gasket...

 

These trucks DID NOT come with these.... unless the 4.2 did.

 

Yea, A bad cap will screw with yuh for sure as well. I lost count on how many caps I've had to blow out and clean with compressed air over the years.

It seems they like to fail the most right after a coolant change. That's most likley because they have to work and work well after that procedure.

Without compressed air to blow them out, I suggest purchasing a new cap before a coolant R&R job anymore. That cap is a pretty big deal, it HAS TO work. If it doesn't that alone could cost you a engine. These engines in particular do not suffer heat to well.

Owkaye, - With the combination of problems that occurred, - trapped air, hot spots and a bad cap, -that could of easily went very bad for that engine. I mean, it got a little tricky, you needed to use your head and you did.

 

This may be true when there's no excess air in the cooling system, but that was not my situation. Here's what I think happened to me -- and if this can happen when the cap is on, it can certainly happen when the cap is off:

- After my drain, flush and fill I unknowingly left too much air in the system.
- The engine pumped my new coolant -- and this excess air -- through the system.
- Some of this air got trapped in a location where it (temporarily) created a hot spot.
- When this trapped air was dislodged, coolant hit the hot spot and instantly flashed to steam.

Now here's a scary fact that I learned while dealing with this situation: When water flashes to steam at atmospheric pressure its volume expands 1600 times normal. THAT'S HUGE!

Since my coolant is an antifreeze/water mix it may not have expanded 1600 times inside my capped cooling system. However I'm guessing that it still expanded enough to force coolant though or past my old pressure cap. But now that there's little or no air in the system to create hot spots I shouldn't have any more "flash to steam" problems ... and with the new pressure cap holding properly for the past two days I'm (hopefully) done with my cooling system maintenance for a while.

 

When the person who works on the cooling system unknowingly leaves too much air in the system and it causes hot spots and high-pressure flash-to-steam explosions it's no wonder they fail at this time!

I think I dodged a bullet this time. But now that this problem is apparently fixed, I notice that I am monitoring my engine temperature much more carefully now -- and that's probably a good thing.

Thanks for the compliment, but you're the one who steered me in the right direction -- several times in fact -- not only in this thread but also in my other thread about the faulty CHT sensor.

Thank you very much for all your help Jbrew. It's people like you who make this forum extremely valuable to folks like me who seldom work on their trucks and need guidance from those with more experience.

 

I went through this same hell last year at this time and spent money on water pump flushes, fill caps. Numerous hours trying to get an air bubble out. Mine did the exact same this, would overflow the fill cap and the guage would peak to hot, shut it off and wait a few minutes and it went down and would run fine untill the next time it was started from cold and warmed up.
It's a small leak from your head gasket when cold till it warms up. I had no coolant in my oil either. I know I'm going to get **** for suggesting this but I used Bars leaks head gasket repair and it's been fine for over 6000 so far. I sure couldn't afford 2grand to do the heads or get a rebuilt motor on a 17 year old truck. It worked for me unless you have the money give it a try.

 

I've been thinking that this might be my problem, too. I haven't been back to this thread in a while (to post my ongoing problem) so here it is now:

Even when I think I have purged all the air from the cooling system, more air seems to get in somehow, yet there are no leaks anywhere on the outside of the engine. Therefore it seems there is only one way for excess air to get in -- a head gasket leak. So here's what must be happening:

The engine forces some air into the cooling system, perhaps at startup (as you mentioned) or perhaps at another time, or maybe all the time. This excess air builds up until it creates a larger air bubble in the cooling system. The air bubble does not move easily through the system, instead it gets stuck at high spots. When it gets stuck it stays there long enough to create a hot spot. Eventually coolant dislodges the air bubble and hits the hot spot, then it instantly flashes to steam ...

The pressure created by this steam bubble forces coolant out the overflow's pressure cap. Now there's more air and less coolant in the system which makes it likely that this problem will repeat itself again, more and more frequently, until the cooling system is finally allowed to cool down, refilled, and is manually burped again. Then all this happens again the next time the truck is run.

So yes, I am considering the use of the Bar's Leaks product you linked to above. It contains carbon micro-fibers and it is guaranteed to work (obviously it may not, but it's probably worth a try). This is what it looks like:




Bar's Leaks has another head gasket / block sealant product too. It is cheaper, maybe because it uses some other kind of fibers that don't work as well as the carbon micro-fibers. Here's a picture of the other one:




My local Walmart has the cheaper one in-stock but I'll try the better one you used, especially now that you've given a review that says it has worked for you for 6000+ miles. I trust your review more than I trust the ones on the company's website ...

 

Snake oil is all that is.

Don't be surprised if all of that settles in your heater core and you have no heat.

 

I'd re-test the coolant for hydrocarbons. Prove it's a HG leak before doing something you may regret.