Heater not blowing hot -- problem found!

[MikeB]

My 82 C10's heater has never blown very hot. On a sub-40 degree day with the fan full blast, the floor is still cool. I mean it's probably 50-60 or so in the cab, but not warm by any means. When the truck is not moving, the air gets a little hotter, but not much.

I thought the culprit might be a clogged heater core or doors (valves) that didn't seal. So I pulled out the heater box and discovered that the core did not fit snugly up against its frame. In fact, I'd say at least 1/3 of the incoming air volume was being blown around the heater core, instead of through it! Maybe more, since the core is actually an obstruction to air flow.

This pic shows the old aftermarket heater core in the frame, which in turn fits in the heater box. Notice the air gap. it's like that on both sides.

P/N 0399079 (Ready Air, Vista Pro, and probably other brand names)


On the left is the new heater core I just bought compared to the one I had. The larger frame seals up perfectly. And as a bonus, the core itself is a little thicker and wider.

Murray P/N 94553 on left. Old one on right.


Perfect fit in frame:


Backside view:


Should have everything reinstalled in a few days, but I'm confident I'll actually have to turn down the heat from the max setting.

[Man With A Gun]

Nice job.

I've got a 65 Buick that's doing the same thing. I might take a look at it next winter.

[S10Fan]

Good info, thanks for sharing!

[MikeB]

Gotta wonder how many guys with the same problem have spent lots of time and money trying to find it by adjusting cables, replacing the fan motor, swapping t-stats, changing hose routing, etc. I have to say the problem wasn't obvious to me until I took a second look at the fit and decided there's no way that GM could have designed it that way.

It's absolutely amazing that Ready Aire and Vista Pro sell their P/N 0399079 as a direct replacement on non-A/C trucks. No way would it ever let the heater work properly, even with 200+ degrees coolant temp.