Take your garden hose and push some water through the heater core, not full force, it should flow with little resistance.

I would change your thermostat, all this changing parts dislodges particles and they get stuck in the little holes.

Park it on a hill again, steep, and seeaif you can work any air out by squeezing the hoses.

 

Bad fan clutch will not cause overheating at highway speeds, I know this because one of my trucks has an electric fan setup with a thermostat control on the fans and they don't run at all on the highway. Perhaps in the summer at idle with the AC on, but not on the highway. I don't really believe the heater core would cause overheating, easily determined by the heat provided to the cabin. If the heater blows hot air, the core is not plugged.

 

Have YOU replaced the thermostat?

 

What state are you in?

 

Would a coolant pressure test not find a head gasket leak ? Which is commonly done around here to test for all kinds of leaks ?

 

I have not replaced the thermostat personally but the previous owner said he had in March and while in route back to southern Indiana, where I live, I took it to a shop to try to have the issue fixed to drive it the rest of the way home and that shop tried swapping the thermostat to no avail. So it’s had two new thermostats this year but none done by me. When I rev the RPMs, the coolant temp does seem to drop a bit so I’m inclined to thinking the thermostat somewhat works but I’m not opposed to replacing it on my own to be sure. When it was at that shop, the shop owner said they did several tests including pressure tests and said “all signs point to head gaskets but I can’t promise that.” So I towed it on a trailer the rest of the way home and did that myself. Aside from all that, heat blows pretty hot once it’s warmed up.

 

I’ve flushed the heater core and radiator and not much has came out. The truck idles at a coolant temperature of 194 degrees with no spikes after that. When I drive it around the block, I make it about half a mile and the coolant temp climbs to 205 and slowly to 210. At 210 (when I believe the thermostat should fully open) I lose heat from the vents in the cabin. Any ideas on what it could be? Thermostat has been replaced twice but could be faulty? Any chance the radiator is bad?

 

Sounds like you could have a couple problems. Air in the heater core, could also be a plugged radiator. The symptoms you describe suggest while the thermostat is closed the coolant is going through the heater core, but once the thermostat opens it does not. The heater core is notorious for trapping air, you need to make sure the heater hoses are routed correctly - look at the rave for that. Could also be a problem with the thermostat - I detest the factory design, much prefer the bypass thermostat mod. Usually if it will idle without overheating but overheats when driving it points to a plugged radiator, but it could be a thermostat not opening all the way (the idle heat could be taken care of with the heater core). To confirm, you can replace the thermostat with a repair bushing and put the top radiator hose on the manifold outlet. If it still runs hot - it is the radiator, if not, the thermostat.

Good luck.

 

post a picture of your thermostat in place. Sounds almost as if the cooling system is plumbed/routed incorrectly.

 

TStat