1991 FJ80 Front heater lukewarm, rear heater hot (1 Viewer)

[mct75]

Thermal pics for fun:

Heater valve closed:

Heater valve opened:

Thermostat housing:

Vents:

 

[JakeVII]

Beautiful.
I'd love to know how 70 degrees are lost in (probably) the heater core.

 

[mct75]

I'm still guessing it is clogged on the liquid side more than the air side. FWIW, my "throttle body heat" lines that come off the thermostat housing and go to the throttle body were completely clogged with rusty-mud-goo. I bet the heatercore is the same way. On a more positive note, that should be easier to clean than taking the dash apart to pull leaves off of it.

 

[LS1FJ40]

I would bet a fair amount of cash that you have debris plugging the outside of your heater core. It is fins just like a radiator. It doesn't take much to plug it up. If you part under a tree or live where it is dusty, the fins are plugged.

FWIW, you can flush the heater core in about 5 minutes when you pull it out to clean the debris off the outside of it.

Total job will take a couple of hours. At most. Unless you are OCD and let it soak overnight.

 

[mct75]

I've got a FSM that's supposed to be arriving today, but overall how bad it is to pull the core? In most things it is a nightmare.

 

[LS1FJ40]

Not that bad. I mean, it sucks but it isn't the end of the world.

Pull glove compartment door
Pull bottom of dash on passenger side.
Remove the bolts holding the ecu (IIRC)
Remove the metal frame across the bottom of the lower dash
Find the 5? (IIRC) that hold the heater core in place and remove

Remember to hook the drain plug back up when done!! It goes through the fire wall.

It's really not that bad.

 

[JakeVII]

Not that bad. I mean, it sucks but it isn't the end of the world.

Pull glove compartment door
Pull bottom of dash on passenger side.
Remove the bolts holding the ecu (IIRC)
Remove the metal frame across the bottom of the lower dash
Find the 5? (IIRC) that hold the heater core in place and remove

Remember to hook the drain plug back up when done!! It goes through the fire wall.

It's really not that bad.

Do you happen to have any pictures of the heater core being pulled out this way?
I thought for sure I'd have to pull the entire dash starting at the steering wheel and work my way across.
It's a huge relief to see that I can probably just drop the glovebox and pull the ECU to get at it.

 

[phoenix60]

reverse flush did wonders for my front heater core on 88 HJ61 when I had same issues.

 

[JakeVII]

reverse flush did wonders for my front heater core on 88 HJ61 when I had same issues.

Yeah, I need to check myself. I should just try the flush before I try to pull it. Thanks!

 

[JakeVII]

This is a great thread for pulling the heater core from a 1994. Pics on page 2 and 3.

'94 heater core R/R - done

 

[JakeVII]

Another great flush thread, this one for a 1992. It has a really, really great photo that shows what to hook up to and what to block.

Front heater core flushed with CLR now producing 135 degree vent heat.

 

[mct75]

I looked at flushing my heatercore this weekend, but IIRC there's a metal tee where the front and rear heat split off, and I don't think I can get to just the front. Would flushing at that fitting just flow through the rear?

I can't seem to find anything in the FSM about the heater cores.

 

[leonard_nemoy]

I had this same problem on my 91 when I got it a couple years ago. I flushed my heater core with a garden hose and some low pressure air. A lot of nasty junk came out and the heat got better. I made sure to use low pressure because i didn't want to risk forcing the heater core to start leaking.

 

[JakeVII]

I looked at flushing my heatercore this weekend, but IIRC there's a metal tee where the front and rear heat split off, and I don't think I can get to just the front. Would flushing at that fitting just flow through the rear?

I can't seem to find anything in the FSM about the heater cores.

The picture in this link shows a pretty good solution to what you describe. The brass spike blocks the hose that goes to the rear core, as far as I can tell.
Front heater core flushed with CLR now producing 135 degree vent heat.

I can't find any FSM stuff either. I'm going to try flushing today, I'll let you know what I find.

 

[mct75]

One roadblock is that I have these weird hose clamps with pins going through them (factory?) so I'd have to find a way to cut them off.

 

[JakeVII]

Oh, those things. Yeah, they're factory. Yeah, they suck.
Have you tried using some kind of penetrating oil to loosen the pins and pull the pin out with pliers while compressing the clamp?

 

[LS1FJ40]

One roadblock is that I have these weird hose clamps with pins going through them (factory?) so I'd have to find a way to cut them off.

If those pins are present the. The hose is original. May consider replacing any hoses that have those pins. They are 26+ years old. They may look ok on the outside but...

 

[mct75]

Excellent idea! I will add it to the list of things to do...

 

[JakeVII]

I flushed it. I didn't get to take photos, but the heat is definitely better. I was promised facemelting, but I'll gladly take the improvement.
Next I'm going to open the exterior vents and see how much gunk I can remove from that side.