Ok so i just bought this truck a few weeks ago. It needed a heater core so i got it for a song. Put the new core in, it had modest heat at the vents. Noticed the temp on gauge was low so i replaced the thermostat with a new 195. Temps on gauge came up and now sit at 190-200. Temp at the vents increased a little but still not hot. I checked the blend doors and they appear to be functioning correctly. In my chasing this issue i checked the heater core lines, they are hot but not uncomfortable hot if you hold them. I checked the upper rad hose (after truck had been running almost an hour) and it was about the same temp as the heater core lines. So i took a chance and pulled the rad cap, no pressure, stuck my finger in the rad at the neck and water was luke warm. I replaced the rad cap,still no pressure . I compressed the upper rad hose by hand and can not feel water going through the line when the engine is running at temp. There is no water/milky oil, but it has been slightly low (just below the neck) on coolant a couple times, and no bubbles in the neck when running, it appears to not be pulling water from the overflow. I have bled the system 2 times so i am confident that its not an air bubble. Bad impeller on the water pump?

 

If it was a bad impeller, it would be overheating. You said you replaced the cap, did you buy a new one or use a used one? If new, you may have gotten a defective one. You should be getting pressure. Not pulling from the reservoir could be an air leak in the hose to it. It only transfers by the vacuum created when the engine cools. Put a hose clamp on both ends of the overflow hose to start with.

 

It was a new rad cap. its been around -15c or 5f here for the last few weeks, I was thinking more a situation where the vanes on the impeller are mostly worn away/broke off but still moving a little water, and combined with the low temps is stopping the truck from over heating. I put a clamp on both ends of the overflow. i wont be able to get the new cap tested till tomorrow sadly.

 

That is a very realistic scenario. Been there, done that, have the pics to prove it.



Some vanes still there, but some are long gone.

 

I do know when i replaced the tstat that it had a crazy low temp (like 160 or something silly). I guess the other option is it was heating on the previous owner due to a busted head gasket and he didnt know what the problem was and put a cold tstat in to stop the heating? not seeing any bubbles in the rad. not worried about fixing the problem as i can do a head gasket or water pump, i just dont want to start throwing parts at it.

 

I don't know how you'd test for the problem in that picture. It's going to move SOME coolant, just not enough, so if you pulled the hoses off, you'll see coolant moving. This might be one of those times you just need to pull it apart and see.

 

As part of your regular maintenance , get some coolant dip sticks, I got some at the local NAPA, particularly to check the pH of the coolant. If the coolant becomes too acidic it will result in erosion of impellers, bearings, and related components. I often use NAPA cool, Schaeffer cool additives to maintain pH balance of the coolant between cooling system flushes. I have had fewer cooling system issues by maintaining neutral coolant pH. The dip sticks will show colors that you compare to a color chart that allows you to easily determine any adjustments or additions to keep your coolant at the proper balance.

 

Well I went to NAPA yesterday and the new cap is good. Sadly they don't have a cooling system pressure tester. A pressure test would be nice to see if its low pressure or no pressure. I am guessing a water pump with missing impellers would make little pressure. So a pressure test could tell me if its no pressure and a bad head gasket or very low pressure and a bad water pump. I pulled the plugs last night and there is no fouling on them. I am really leaning towards the water pump as i have no symptoms of a bad head gasket other than the couple times the coolant has be a little low with no obvious leaks. Unless i can find a way to pressure test it today I think I have little else i can do diagnostically at home to determine my problem, and will probably just pull the pump and see what i can see.

 

Under the impression that not all Napa's rent tools.
Mine does.
Pretty sure Auto Zone and Advanced do.

 

It is my understanding that fluid expansion creates the pressure and since the water pump is a centrifugal, it creates flow, not pressure. Therefore the cap determines pressure and without pressure, the coolant boils at near 212* and once steam is generated, pressure goes up exponentially! I really don't understand what's going on with your system at all. Your thermostat may be defective even though it's new.