Weird Overheating Problem

[Jed_Kent]

Ok so I have had issues all summer with random overheating, not head gaskets already tested for it. Did a pressure test and it hold without any loss. Replaced the Radiator, expansion tank, hoses, cap, fan and clutch. So it is no longer summer temps and we are now down in the 20-30s this week. Started the truck and let it warm up before driving. Got into it and the heater was cold and the temp was climbing higher than normal. Checked under the hood and it was not an air issue their was not much pressure in the hose at all. It looks as if the water pump is not working at all but it is not wobbling or leaking or making any noise for that matter. I mechanic I know (thirty years of working) said he has ran into a problem like this once and it ended up being something with the water pump where it free spun on random and worked 98% of the time but had random overheating. Anyone else have an idea of what I should do? I did drive it with the a drilled out thermostat and it ran way to cold for a week before I switched back to the 180 in there now. Thanks

[Bosnian Discovery]

No heat + overheating sounds like you could have an air lock in the system. Did you bleed it properly?

Have you checked your belt routing? If you route it wrong there is a chance that the fan could "push" instead of "pull" air and the water pump could flow backwards creating problems like the ones you have.

Also, if you haven't replaced your water pump, do it. A replacement (that's better than stock) only costs $175.

[Jed_Kent]

it is bled right and the belt is right. No air lock. The heater works right now when I started it but that is what I am talking about the pump works at points then at random stops.

[Bosnian Discovery]

It's next to impossible for the water pump to fail intermittently. Its just a pulley pressed onto a shaft that spins the impeller - quite a basic system. If the pulley is spinning, the water pump is working. Rev the engine in idle and you should coolant surge in the expansion tank - signifying that the pump is working.

Do you have any evidence of a failing pump?

[Disco Mike]

Are the heaters hoses hot or cold? It could be a bad t/stat, not routing the coolant to the heater cores as it should. As for the water pump, if it is original, replace it to rule it out, might use the one from Airtex with the brass impellor that is sold at BPoU.

[Jed_Kent]

I did the boil test with the t/stat and it is doing what it is supposed to. Heater is cold.
I will check it again today since I have to move it anyways.

[Jed_Kent]

So today I took it for a short drive and let it get up to temp (186F) it stayed in that area while driving but started to climb to the low (190s) at stops. If I rev the motor a little bit the temp starts to come down. Could my belt need replaced? I figure maybe the belt is not making enough contact or I know people say this does not happen unless you work at napa its a common problem and that is the fins on the pump wear out? I got a pending missfire on 8 this morning at startup but it did not return after that.
Heater did work also.

[Bosnian Discovery]

186F-190F are actually really good temp readings, what is your concern? How high have your temps gotten?

[Disco Mike]

Jed, send me you number and lets talk about this.