Obviously I hope you're right, but I'll do my cold engine tests tomorrow before I believe this for certain.


Yes, I understand this, but if there's a valve on a heater hose or on the heater core itself it can be closed, and then the coolant won't flow through the core. I was just wondering where this valve might be ... or if there is no such valve on these trucks?

There's no radiator cap on my truck, only a cap on the plastic overflow reservoir. And although coolant flows into and out of the reservoir via a single hose connected to a tee in the lower radiator hose, the reservoir is not "in the loop" of coolant flow. This is why my approach to your suggestion was to feel the top radiator hose to make sure it got hot thus indicating that the thermostat was open, and then squeeze the hose in order to help push air into the reservoir so it can get out of the system.

In addition to doing this, I also installed a tee-with-cap in the top heater hose so I could fill the system from there when cold. This allowed air to escape from the heater core as coolant was added.

 

Two points for you! You are smarter than the average troll. You got something right. Sort of. The 'trick' is to touch the hose some distance away from the tstat to make sure you have fluid moving and not just heat.


Of course I am sure you have a much better way.

 

Are you sure tstat isnt installed upside down?

Right tsat with bleed valve ?

Wont put air in system

But might cause erratic coolng operation and overheating

 

I installed it spring down, just like the one I removed which was in there for 7+ years and working fine. Yes, it's the correct thermostat, and yes it has a bleed valve. I've proven that it works fine by feeling the top radiator hose -- which is always cool to the touch until the engine gets warmed up, then it gets too hot to touch for more than a few seconds without gloves.

 

I ran my cold-start hydrocarbon tests this morning -- continually from before I started the truck until 10 minutes after it had reached normal operating temperature. This took about 1/2 hour, more or less.

Results: The test fluid remained blue the entire time, which suggests that the head gasket is NOT leaking!

So here are my observations while I stood in front of the truck during its warmup:

1- At the start the coolant level was at the lower range mark on the overflow reservoir.

2- As the truck was slowly warming up at idle (but before the thermostat had opened) I watched the coolant level rise gradually, about 1-2 inches. I squeezed the top radiator hose a bit to see if this might dislodge the air bubble that I presumed was pushing the coolant higher in the reservoir. It worked a little bit but not that much yet.

3- The truck kept warming up and eventually I noticed two things at roughly the same time: The top radiator hose was starting to warm up, and the coolant level was getting higher and higher -- very close to the reservoir neck. So I removed the testing tool and started squeezing the top radiator hose again. This time after each squeeze some air moved into the reservoir and the coolant level dropped.

4- From then on the coolant level stayed within the fill range on the side of the reservoir. But the fact that the coolant had risen so much that it almost overflowed brought up a question:

Should I switch to a cooler thermostat?

I just installed a new Stant 195 degree tstat. I did not test it before I installed it, but I'm thinking that if I install a cooler tstat then maybe it will "get the coolant flowing" through the radiator sooner, and maybe this would prevent coolant from rising all the way up to the top of the reservoir.

Why does the coolant rise so high in the reservoir as the truck is warming up?

Might a faulty water pump be causing this situation, perhaps because its impeller is mostly gone so it can no longer push coolant through the system "fast and hard" enough to avoid this kind of problem?

It seems to me that if coolant were being pushed through the system with enough force, maybe it wouldn't develop the "air lock" that I think it's developing now ... and then maybe the coolant wouldn't get so high in the reservoir.

???

 

Imo, i wouldnt go cooler on the thermostat- the PCM uses the engine temp.readings- ( on my old Explorer, when the thermostat went bad, the gas mileage would go to crap.)My guess is the PCM uses the engine temp.( among other things) to determine fuel input.

 

You have the correct thermostat and i suspect changing it would do nothing but harm, plug your PCV valve and ruin your fuel mileage. I think JBrew's suggestion of checking the water pump is the next step.

/edit - I think you already answered why the coolant level is rising; there's air in there as proven when you squeezed the radiator hose. We still just don't know where all this air is coming from as it seems the HG is intact. JBrew is quite experienced... heed his advice and tear off the water pump next.

 

Don't go cooler on the stat. Bonehead rookie mistake. Reasons? See Bears post (#46)

Take the water pump off like Brew said. Don't beat your head against the wall any further. Check the pump!

 

It rises up because a gas pocket is expanding as it warms up.

There should be no.gas pocket, and level should be rock steady, hardly changing between hot and cold.

Stick with correct tstat.

Top radiator hose may always have air. Radiator has air at top. Its vented to reservoir with small tube to equalize.

 

OKay, I'll remove the pump and see if that's the problem. And I'll stick with the new and correct tstat.