Low Heat on Low, No Heat on High

[DryDog]

This isn't a real hi priority because it warms up enough that I don't see my breath but...
.
My 91 X puts out about 85 deg F from the vents (75 from the floor) if the fan is on low. The higher I turn it up the colder it gets. Max heat is abot 50. Outside temp was 8 today so it's still better than that.

I did not see any 91s on the Blend Door Fix threads. I can hear something open and close when I move the temp slide. Radiator is full, I can watch the T-stat work on the temp guage. I never have got much heat out of it this winter. Could it just be an adjustment??

Matt

 

[savant]

My 1991 is doing the exact same thing. If I leave it on low, the heat is fair, if I turn it on high, it's pretty cool air coming in. Like you, I can hear my blend door slapping when I turn it over to hot...

I have no idea what to do about it, but what I have done is put some cardboard in front of 1/4 of my radiator. I could probably stand to cover a little more. It helps prevent the radiator from cooling the coolant down quite so quickly, and seems to help warm things up a little.

Does anyone have any fix for this? It's chilly out!

 

[TPLYNCH]

Heater core is probably plugged. Try flushing it.

 

[savant]

That's a good idea, and I'll definitely check it out. I'm going to be befuddled if it ends up being a plugged heater core though, given that I've flushed the system no less than five times in the last two months. (!)

 

[mctoy]

Do your trucks get up to normal operating temp. at all when its that cold? I'm an HVAC guy (Own my own co,) and what you are describing could be as simple as 1. not enough heat present at the coil due to ambient temp. and/or 2. on high speed, the air doesnt have enough 'contact time' with the coil to pick up much heat. When a home furnace doesnt get the proper heat rise, the solution is to slow the fan speed down. Covering a portion of the Rad. will give you hotter coolant/warmer air. Watch your guages!...Hope this helps some.
Was born in Ind....Brrrr!

 

[DryDog]

The last flush I did was in Oct with a T fitting into the heater hose. I flushed til it ran clear. I did not do a chemical flush but it was enough to clean the crap out of 2 cracks in my head. I am hoping for other options other than another flush. I'll have to wait for spring to find a hose that will flow.

My temp guage seems to be working. It starts deeply buried under N and rises to a quarter after 10 or 15 minutes. Sometimes it does rise over to the A or L for a few seconds, then falls back to N-ish. It does this on the highway which would put the wind-chill at -20. This kind of bothers me.

The heater-core cover feels hotter than the air coming out of it. Today cabin temp was a refreshing 50 deg.

 

[DryDog]

I guess the moral of the story is to listen to someone who has more than 2000 posts! I removed the heater core to the deep sink in my shop and flushed it there. Some chunks came out and it heats like a torch. Thanks!!

 

[TPLYNCH]

You're welcome. I try to advise the simple things first. 95% of the time it works. Glad it worked for you.

 

[savant]

Just wanted to post an update. While I was doing other repairs last weekend (fan clutch and power steering pump this time) I pulled the hose that leads into the heater core and then ran the vehicle for 15-20 seconds. It belched out what seemed to be a rust plug. It was very fine, and fairly thick.

Guess my poor exploder had clogged arteries. The heat is now enough to roast me out, even in 0 degree weather. Thanks guys! It's no fun driving a freezing cold truck.

 

[mctoy]

Good deal! When you said you had flushed 'the system' I just assumed you had flushed the heater and hoses out as well as the Rad. in your earlier post. Anyways, glad your not freezin' anymore!