need help with heater core

[C.B.'s 72]

My truck has no love for me. Heater core took a dump. What is the process for removal and replacement. Looking at different places I think that it might have been hooked up backwards. The hose from the water pump does it go on the top or bottom? Thanks for taking a minute to help.

[COBALT]

First, is it AC or non-AC? There are two types. AC heater cores have a funky in/out, with an acute angled connection. Non-AC is your real easily identifiable rectangle with 5/8" in and 3/4" out (bottom and top). You can get them at NAPA for about $35.

Second (if non-AC) the inlet to the core runs from the intake to the bottom of the core (5/8"), and return coolant from the core comes from the top and runs to the water pump (3/4"). Heatwise hot fluid comes from the intake, and is dumped out by the heater core before returning to the pump cooler than it went in. If you have it mounted backwards then your coolant flow is the same (from 5/8" to 3/4"), but the coolant is going with gravity rather than against it. That shouldn't make the core "take a dump", but it might effect heat transfer. You want coolant in the core as long as possible to get as much heat out as possible.

Third, changing it can be a pain depending on the condition of your heater box. If you have non-AC like I do I ended up unbolting the hood hinge at the bottom, and sticking a wood block under it on top of the wheel well to get enough clearance to get it out (you have to take the heater box out).

If your heater box is in bad shape it might be worth it to get a weather stripping and sealant kit from LMC. They include all the foam pieces plus the weather stripping to seal up the box to keep the hot air either inside the box, or transferred to the cab (and not to your engine compartment).

Strip the box down and clean it. The heater core is held in place by two metal rods that are bent to hold it. There's a couple of sheet metal screws to take out. Oh, and also: lube the mechanism that shuts the heat door, and make sure you get that heater control loop back on the little peg when you put the heater box back in!

Have fun.

[C.B.'s 72]

Cobalt thanks for the detailed info. It is a non A/C and it was hooked up backwards then. When you talk about the heater box is that the piece on the floor of the cab or the cover over the core in the engine compartment. Thanks

[SEVEND2]

Mine runs from the intake to the Top of the core and from the bottom to the radiator

[cruzn72]

I think the heater box Cobalt is talking about is the big ugly box in the engine compartment.

The one thing he did not mention is the nuts on the bottom of the box. There are studs coming out of the cab that hold the box on. I do not know if there is a secret way to get to the one nearest the fender, it is a pain. I guess you have to take off the front sheet metal, yeah right. We finally drilled a hole in the inner fender and put a socket with extension through to get to the nut.

The first time I under took this journey, I took the hood off. What a mistake that was. I had to replace another core last winter and left the hood on. I can't remember how I got the box off but it came off and went back on.

Hope this also helps.

[COBALT]

Yeah there's some debate about how to get the box out. If you're clever and have patience you can get the box out without taking the hood loose. I was impatient.

The nuts are a pain.

As for the flow I always assumed it flowed up. Gosh, maybe I'm backwards!

[Blue Beard]

Drop the inner right fender, can be done without much trouble. Just let it hang.

and don't forget to replace the gasket to the firewall while its out.....