I'm not saying this is the problem, just a caution.

I installed a rebuilt motor that had been sitting on a shop floor for some time. In hindsight I will never again install a motor without first flushing the coolant system. A mouse had made a home somewhere in the coolant passages, and upon startup of the fresh engine, my rad and head got plugged.

Maybe check the system with an infrared thermometer?

 

Was the hose cold, warm or hot?
Ouch! That hurts.

 

Cold.

 

Either your thermostat is not closing or you are not getting any water flow for some reason. Is your engine overheating? Do you get any warmth at all out of the upper radiator hose?

 

I've tried 2 new thermastats. The engine stays at 205° even drove it and never over heated. The upper does get pretty warm but stays soft no pressure.

I know you can get bad parts from the auto parts store but a water pump ?

 

If your engine is running steady 205, I wouldn't expect the water pump. Your heater core could be air bound but I don't know how. If you backflushed it and water came out, it's flowing. And I never had a problem there. Have you taken it for a hard run on the road?

 

I have a couple thoughts on this:

The fact you are seeing a constant temperature and seeing the coolant rise and fall strikes me that your water pump and thermostat is working. What temp thermostat are you using? OE is 198.

It strikes me that you are dealing with an air filled system or a blocked heater core, though you did flush it. I flush it in both directions.

Assuming the heater core is clear, I really lean towards the system needs to be burped. I have personally found that it can a very slow process on these trucks. Having both front wheels on car ramps, I will stand there with a small container of 50/50 coolant and as the coolant lowers I'll add just enough to the radiator so that when it rises back up it won't come out of the filler neck. I use a stubby funnel that fits somewhat snuggly in the filler neck. I've already had times when it has taken me over an hour and many thermostat opening times adding coolant with small pours.

My theory is that in some places air gets so trapped, what you see rise and fall will not change until you add coolant to displace the air and get it moving to the high point of the open radiator cap. I'll sometimes be sure I'm done only to add a little more and watch a couple air bubbles "blurble" up and the coolant level in the radiator go down a touch lower.

 

Actually getting ready to drive it on an hour round trip to see what it does.

Ya the thermastat is a 195° and I tested it before install judt to make sure it worked lol.

I'll try the method you said with both wheels on ramps. Because every so often not much, but I do get a couple bubbles. This is when I had one wheel up.

 

I do have to note that on some pours I guess wrong and add too much so I keep a rag wrapped around neck to catch spillage.

 

One thing I forgot to mention while burping, I'll frequently reach over to the throttle body and bring up the RPM. I do this for two reasons, to get thermostat to open faster and to do a little throat clearing of the cat.