Heater core on a D1200 T-all

[MarkO]

Yesterday I was driving along and wanted to turn down the heat.

When I pushed in the heat control coolant started pouring out of the heater core.

Pulling out the heat control basically stopped the coolant leaking.

Any idea as to what happened?

How does one get into where the heater control valve is located?

I have the shop manual and it isn't doesn't say anything about the r&r of a heater.

I have the large heater with two fans.

 

[Michael Mayben]

Some (but not all) of the "heavy duty" heater assemblies have two temperature control valves.

One is operated from a bowden cable and was originally mounted in the intake manifold hot water passage, that is the heater core inlet side. However, it might have been removed or was never installed at the point of assembly.

The valve that is leaking is inside the heater box between the two cores. It's a bitch to access, the cover has to come off from the engine side of the bulkhead, and the dash are has to be gutted out also. Lubricate the motor bushings while it's torn apart, I bet that motor squeals when it's cold.

I don't know where this pic came from, it's not a job I did, but it does show the valve in question.

 

[MarkO]

That looks like mine.

The only thing on the engine side of the firewall are the inlet and outlet pipes and what look like a couple of studs that must be holding the heater assembly to the firewall.

My heater looks to be completely under the dash.

From your picture it appears as if I will need to remove the whole assembly to do anything.

And yes the fans squeal worse than a miser who has to pick up the tab.

What do you suggest for lube?

 

[Michael Mayben]

Here's the two different systems that were offered as the "heavy duty" units, one is heater only, the other is integrated hvac. These are the pages from an mt124 parts list.

And as you can see, these illustrations are not very full featured...don't show the relationship of the various cores to the other parts. IH spent alotta rhetoric in "how the stuff works" but gave no detail in how to r&r much of anything!

And neither of these illustrations May be exactly the same as what yours is! But you can see the "internal" temperature control valve in the callout if ya look real close!

When ya pop the nuts off the studs on the engine side of the bulkhead and remove the hoses, the front case cover will come off, there is also a thin foam seal that you will prolly need to replace with something else when ya re-install it.

I have a front heater case cover on the bench now for a standard heater assembly. Belongs to a club member who is having a motor built and the housing is damaged. So I'm doing some fiberglas work on the case cover, it'll look as new when completed.

The ihc heaters systems were pretty straightforward...but the integrated hvac stuff was real crap. A combination of electro-mechanical, vacuum, and bowden cable controls! Whatta pos and service nightmare!

What I find on the heater motors is that the rear bearing is dry (it's an oilite bushing). So I drill a 1/16" hole in the "bump where the end of the motor shaft would be and then shoot in several shots of a solvent-base lube (not wd-40!)...something like superlube with teflon. Do that while turning the shaft and repeat a couplea times. Then put a dab of duct tape over the hole to keep the mice out.

Best case is to teardown the motor and polish the shafts and clean the bushings/brushes/etc. Then I'm now using that lucas "synthetic" wheel bearing grease for lubing stuff like the motor shaft/bushing interface. Or anything that is moly-filled.

 

[MarkO]

Well, here it is halloween and I finally got the heater fixed in the t-all.

As I suspected, the heater control valve failed.

What an absolutely miserable place to mount a valve. Also, what an absolutely stupid way in which to mount the valve.

I can understand why everything is mounted inside a single box (a lot easier to upgrade from no heater, to standard heater, to high capacity heater). But it is still a wacky design.

Since I had to get the core out to service the valve I took the core into the local radiator shop to test it. It tested okay with no leaks (I figured that if it was already out to have it tested would not be a bad idea. I would have hated to put it all back together only to discover the core was leaking as well).

I eliminated the valve inside the heater assembly and put a universal fit valve under the hood. The stock control cable was more than long enough to still do the job in a different location. If the all plastic valve should fail it will be much easier to replace in the future.

Moving the valve required some redneck engineering to get the heater hose to go through the firewall without rubbing anything. The hose had to go through a couple of 90-degree corners in order to get through the firewall but the hose is loose enough that it isn't going to get kinked.

All potential rub areas got wrapped with a split section of heater hose and then wrapped with tape. It will take a lot of rubbing before the hose gets a hole rubbed through it.

I took mm's advise and drilled a little hole in the end of each of the blower motors in order to spray some lube on the bearing. Now when you turn the blowers on they don't screech and holler at you all the time. Again, a really dumb way in which to mount the blowers for easy r&r.

Now, as soon as the temp hand starts to move I have lots of hot air blowing out of the vents.

Thanks mm for your insight on this repair!

Your help and insight is invaluable.