So of the many little things to fix on my old truck, the heat output leaves a little to be desired. Being as it's all 41 years old, I'm going to replace most of the cooling system. Hoses are original, in fact I've got a pinhole leak in the heater hose coming off the water pump. I have a new timing chain to put in at some point, so I might as well get a new water pump since I've got to take it off.

Looking at heater cores there are a couple of different options: high output and standard. The difference seems to be an extra 1 1/2" height on the high output unit. Beings how it's winter here in Nebraska, I'd rather have as much heat as I can get out of it so what I'm wondering is whether I can put the taller heater core into the box if I don't already have it.

 

I did that exact thing once on the first 78 F150 I had. I remember having to cut the enclosure so the corner of the new core could stick out...it was hack but it worked.

 

no; but if you are determined and handy, probably. You SHOULD look for a Hioutput housing and just replace, direct replacement. If you cut the little plastic provision it will aqccept the larger heater core into the std. housing. It will help. Find a genuine copper core over aluminum and be way happier after getting over the thinner wallet.

 

So the box is different? Is there a way to look at a box in the pick-and-pull to see which one I'd want to get? It could very well be that I've already got one.

 

On the dash there was a glue on placard that says HIGH OUTPUT between the radio and heater controls. It could have been pried off or fallen off over the years.

The heater boxes themselves were sometimes stamped with High Output in yellow or white lettering, which you can see when poking head under the dash.

Other than that, if you dont know the physical difference on sight of the 2 box shapes, not anything else to add.

Might be a trim level option, or a regional option, I don't recall right now.

 

You might try cleaning the coolant system with the prestone cleaner or similar. I went from almost no heat to plenty warm because I wasn't getting flow through my heater core. The stuff I flushed out looked like iced tea. Just mix distilled water with the coolant flush and drive it that way for a hundred miles or so (in warm weather because you're not running the anti-freeze for this) then dump the mixture. Repeat as necessary until the mixture looks about the same color it went in. If you think your heater core is already clear and it's just way colder where you are, then you probably do need the hi output core.

 

I read somewhere that the Dentside High Output heater box and core are the same as the heater box and core for a '69-'70 Mustang.

 

I am determined and handy, but I'd rather just find the right box for what I'm trying to do. Mostly a matter of time: I could spend days modifying my box for a bigger heater core, but why do that if I can simply plug and play the right box.

So where would I get a copper core unit? Is that something I could get at my local NAPA or is there a specific supplier?

 

I am going to have to flush it out when I put a new water pump on, otherwise the warranty for the pump won't be honored. At least that's how we do it at the shop I work at. I could do it at work actually, we have a couple of different machines to flush a cooling system and we have some pretty slick chemicals to clean it out. Generally we use a two part BG system for coolant flushing, but we also have something from NAPA that works pretty well. I did drain some coolant yesterday to replace my coolant temp sensor and my coolant was a little murky. Plus I'm 99% sure I'm running OE hoses all round, those should have been replaced long ago.

 

C6OZ-18476-B .. Heater Core-Use with Fresh Air Heater / Obsolete

1973/79 F100/350 & 1978/79 Bronco with High Output Heater // Use with heater without factory A/C: 1966/67 Fairlane / 1966/70 Falcon / 1968/72 Fairlane/Torino / 1971/72 Mustang/Cougar.

The truck heater (high output or not) is not the same as any year Passenger Car.

 

So looking at my box, I'm not seeing anything that says it is a high output. Next question is; how do I get the box out? I gather that it's easier to remove the dash first but I'm not entirely sure where the bolts to remove the dash are. If I recall there are two bolts to a bracket which also holds the steering column, one bolt at each lower corner but are there other bolts holding the dash in?

 

Sometimes there is a brace under the dash below where the radio/heater controls are.

 

You shouldn't need to remove the dash, I was able to get my standard heater box in with no problem after I'd already installed the dash in my truck.
You first want to detach the cables from the 'input levers' on the box.
Most if not all of the box's fasteners are outside on the firewall. Shouldn't be more than three or four. And as I remember, the outboard side of the box engages with the plastic piece which is screwed to the passenger kick panel, where fresh air is sourced from the side cowl vent tank thing. I don't think there's a screw holding those two pieces together, there wasn't on my truck IIRC, but it's something to look out for if it hangs up.

If you're worried about the core spilling in your cab as the box comes out, you can pop a short length of heater hose on each of the core bungs, and then find something to plug the ends of the hose stubs. This won't help if the core has puked into the box.

Plus I went back and found the thread I'd seen where they used a Mustang heater box, and it was indeed from a '71 Mustang.

 

 

If it ain't leakeing, I would just backflush with air. Disconnect both lines to the heater core and blow compressed air through each till there's no crud coming out. DONT use full pressure just an airgun you can feather the trigger on. That usually does wonders for crappy heat.