Heating issues

[Zachtheame]

Hello everyone I’m new to this forum so I hope this is an acceptable topic.

I have a 1996 K1500 4.3L and I’m having heating issues. Started off with no heat and ended up needing a thermostat. That worked for a winter and now we’re back again. I determined the heater core was not allowing fluid through so I put a new core and hoses in and confirmed fluid is flowing as well as another 195° thermostat just for good measure but the truck still has questionable heat. Where should a guy look next? It runs pretty consistently at 170°F despite the 195° thermostat.

 

[richard wysong]

Are both heater hoses about the same temp?  if not the core is restricted still. if so the blend door or actuator is probably stuck or not working. does the truck have a/c and electronic control or no a/c cable control?

[Zachtheame]

One line is 122° and other line is 95°

I have confirmed the blend door is moving

the truck has A/C but it was added after the fact by the dealership

[It's Tim]

1 hour ago, Zachtheame said:

as well as another 195° thermostat just for good measure but the truck still has questionable heat.

What brand?

If not OEM then Motorad is one to look for.

[richard wysong]

sounds like there's still a restriction in the coolant lines. maybe in the fittings for the heater hoses on the engine? Does the return line go to the radiator or the water pump? Inlet temp should be the same as engine coolant. You could reverse flush the heater core with a garden hose just to make sure it's clear

[Zachtheame]

We replaced the inlet and return lines completely except for the metal tube section in the middle which we cleared with a wire bottle brush. If there is an obstruction it would have to be within the water pump itself but I pulled the outlet line off and ran it and the flow seemed as free as I would expect it 

 

The supply line originated in the block and terminated at the water pump 

[richard wysong]

you got your self a real head scratcher! you replaced the Fitting on the intake manifold ? The oem fitting was a quick connect aluminum deal that was prone to corrosion. Even if engine temp is only 170 you should have good heat. as stated if the heater circuit is clear the inlet should be same temp as engine and return only a few degrees cooler at 1200 rpm 

[Zachtheame]

We sure did, the fitting snapped when we tried removing it necessitating it’s replacement. It sure is a head scratcher, we’ve tried everything. And it’s something that happened between this year and last year because the heat was stellar last year 

[richard wysong]

some radiators have a nipple for the return line that would be capped off where yours returns to the water pump, if you have that you could switch the return to there and cap the water pump nipple and see if that helps

[Zachtheame]

Any chance you have a photo of the extra fitting? I don’t see any but I don’t know where to look 

[richard wysong]

Right side just below the rad cap, not all rads have it. if you are 100% sure the core and lines are clear I think the only other thing it might be is that the passages in the intake manifold may be blocked by corrosion which would entail removing the intake to check and clean although you maybe able to check with a borescope camera if you drain some coolant

[richard wysong]

Either Lisle or KD makes a heater flushing attachment for a garden hose that has an air fitting on it to give a blast of air along with the water. I added a water shut off to mine  to save going to the spigot to shut it off

[richard wysong]

when you removed the return line from the water pump there should have been no flow from the water pump nipple with the engine running and strong flow from the return line. A defective heater core is a VERY remote possibility BUT if there is good flow the lines would be the same temp so probably not that

[Zachtheame]

Well I replaced the heater core and lines so that’s already been eliminated and there is good flow coming from the return of the heater core so I am starting to suspect the issue is on the return side

[richard wysong]

I have never seen a problem in the water pump but I guess anything is possible. Its not a hard pump to r&r  to check it.  No nipple on the rad I take it.