Symptom. Heat is warm, not hot. Vent is cool sliding over to hot, it gets slightly warmer but not much. The temp guage is working = Thermostat good. The hoses near the firewall are warm to the touch.

I've read a few threads here and I think I need to replace my heater core. Picked one up at Napa. This requires pulling the dash. Yay!

Before I dug into this I pulled out my 85 FSM and can only find info on AC. However the electrical diagram in the back says its on the 15 fuse with engine. Replaced that even though it was still good. I've driven it 30 minutes still only faintly warm.

Another problem I'm having right now is my blinkers and my hazards don't work. I'm thinking I should fix that first. According to the FSM it states the 7.5 fuse is the one. Fuse is good. Solenoid?

Any suggestions for me as I dive into this mess?

Thanks in advance.

 

Replace the fuses.

Flush the heater core as its probably just full of 25+ years of gunk.

:wabbit2:

 

what could have happened is that the heater hose coming out of the firewall has bacome detatched, causing the heater to suck in mostly outside air rather then engine heat. or your vent that sucks outside air (assuming you dont have a/c) for the summer time, could be stuck in the open position due to broken linkages.

ive had the blinked/hazard/horn problem in my 85 and it wasnt the fuse inside the cab of the truck, it turned out to be the fuse under the hood (stumped for a while too) wich also has the alternator on it if i remeber correctly.

hope this helped.

 

Good stuff. I've replaced the fuses. Its blowing hard, just no heat. The heater fuse is under the glove box, checked that and its fine.

I have the book Fsm but also searched on HEATER by downloading the pdf http://www.ncttora.com/fsm/1985/1985FSM_OCR.pdf

Thanks 85, I'll check that out.

 

Im having the same problem. But i think with mine the engine doesnt get warm enough. When i sit for 10 or 15 minutes and let the engine warm then i have heat but if im driving it never warms up enough. I just put cardboard on my grill and that is helping a little bit. My vent under the steering was open but shut that and still not good heat. So will be interested in what you find.

 

I pretty much have experienced everything you guys have. Hose are hot to touch, truck is to proper temp., flushed the core, got the air out of the system. It seemed like the heater was working but now it sucks. I ordered the resistor and heater core and plan on replacing it all this weekend. I'll let you guys know how it goes.

 

Thanks Waskilly,

I had it flushed by Jiffy Lube 6 months ago - They don't flush, they suck and fill. Suck old fluids out and refill.

A thourough flush is what it needed. Its blowing so Hot now that I have to turn it down and this is in a 21' motorhome so there is lots of space to warm up.

Going forward if this happens

1. Check all fuses
2. Flush the radiator, anti freeze systems professionaly, not a Jiffy Lube store.
3. Replace the thermostat

4. Many other things before you PULL THE DASH APART. The guy down at the rad place says you RARELY ever need a new core. You just need a good flush.

Thanks for all the help!

 

Glad it worked out for you.

Easy to flush yourself.

:wabbit2: