Heater issues with 2000 Expy continue

[mangus64]

Folks, I posted last winter regarding this as well. I've got barely warm heat when driving on the highway. I've checked the heater vent, replaced water pump, flushed system multiple times, replaced t-stat.

As of now, after driving 25 miles on the highway, top radiator and coolant hoses are just warm to the touch. I suspect two things now, one I have air in the system and read to elevate the front end and burp the system. Also, the thermostat must not be doing its job as the engine simply will not get hot. I'll rememdy both the next few days.

Question, is it possible for the heater cores in these rigs to be plugged but yet still flow coolant i.e. are they like a radiator where a few tubes can be completely plugged but the coolant bypasses them flowing normally but just not conducting any heat?

Thanks for any help!
Mangus

 

[Thermo]

mangus, as for your problem, odds are you are looking at a thermostat that is stuck open. So, replace that first and then see what you have.

As for the heater core, that is a single pass setup and it is essentially one long tube with fins on the outside. So, it is completely different than the radiator.

The only other thing that I would tell you to look at is the water pump. IT is possible that the pump simply isn't pumping enough and you are trapping all the heat inside the block. Granted, I would think that the temp gauge on the dash would reflect the hot condition. Along those lines, is the temp gauge on the dash sitting where it normally sits (about 1/3 way up, atleast on my truck that is where it sits) or is it sitting lower? If it is lower, then I would be looking really closely at the thermostat. If it is reading higher, then I would be looking more at the water pump.

 

[mangus64]

Thanks Thermo. I replaced the water pump last January during round #1 of this heater problem. Replaced the t-stat yesterday, second new one from Napa. It's making heat about the same as before.

Temp guage sits right in the middle pretty much when the top radiator hose is barely warm to the touch or when the system is about boiling over because I've covered the radiator to force it to get hot.

It acts like it is bypassing the thermostat, have never seen the actual coolant circuitry on this rig but that's what it acts like.

To conclude the only way the top radiator, heater hoses get hot (so hot you can barely touch them) is to block the radiator with cardboard and drive it. Doing so also builds good pressure in the hoses.
Otherwise, the hoses just get warm and not hard and barely warm heat is the resuult..

Any advice, tips, help greatly appreciated. I'm about done fighting this thing

mangus, as for your problem, odds are you are looking at a thermostat that is stuck open. So, replace that first and then see what you have.

As for the heater core, that is a single pass setup and it is essentially one long tube with fins on the outside. So, it is completely different than the radiator.

The only other thing that I would tell you to look at is the water pump. IT is possible that the pump simply isn't pumping enough and you are trapping all the heat inside the block. Granted, I would think that the temp gauge on the dash would reflect the hot condition. Along those lines, is the temp gauge on the dash sitting where it normally sits (about 1/3 way up, atleast on my truck that is where it sits) or is it sitting lower? If it is lower, then I would be looking really closely at the thermostat. If it is reading higher, then I would be looking more at the water pump.

 

[mangus64]

Any real chance the fan clutch being locked up would keep this thing cold? It's in 20s and 30s up here in Montana now.

 

[Thermo]

mangus, if the fan clutch failed, to make it do what you are talking about, you would be blowing major air through the engine compartment and I would think that you would notice that. Granted, pop the hood and start the engine. Rev the engine by hand and if you hear the fan really roar, then it may be that.