Heater with no heat: Revisited

[TIMSPEED]

Well, guess what? I put my hand down by the heater vent while driving...the air is like just normal air, not even hot. BUUUT, I parked for a few minutes in taco bell parking lot, and after a few minutes of idling, the air got a little hotter. ALSO, I thought my coolant temp guage was broken..turns out, it's NOT! My truck just DOESN'T get warm AT ALL. (Coolant wise) I guess I gotta replace that belt-driven fan, with an electric one, so it'll give the motor a chance to warm up, instead of always running at like..160º. Or I might just swap my theromstat for a higher temp also...(180º currently, might put in a 195º)

[ElGracho]

Sounds like a stuck open thermostat to me. The fan shouldn't make a difference if the thermostat is working. If it isn't hot, the thermostat should be closed and there will be very little coolant circulating through the radiator (and then getting cooled by the fan) so it should still heat up.

[phantom dually]

I agree check the thermo and replace it while your there. Go with a 165 degree

[PHOENIX]

I agree something doesn't seem right. Even if you are running 160 degrees you should still be getting hotter air then normal air. Remember a heater core works like a radiator except the heat being pulled off the heater core is then blown into the cab. If your truck is ever running hot you can through the heater on and its like having an extra little radiator, with a little electric fan to boot
Doesnt help a whole lot, but can help when pushing a car too far in the heat. Remember those videos I posted of the v6 firebird (the ones that shut swervins site down, sorry swervin), well we had the heat on almost all the time or else the car would over heat. The car had its day and thats about all we could do to stop the overheating.

I say check your thermostat and check the doors in the heat system. Are you sure they are opening? I guess it is possible you could have done something to them when you replaced the heater core not long ago.

[allthrtl]

First, change the thermostat, either way, it probably needs it...I'm not positive how it works on these trucks, but you also want to check and make sure the door in the vent system is opening and closing properly, you can hear it when you adjust the temp selector(cool<--->hot)...If it's not working, then air isn't going thru the heater core and therefor isn't going to be warm...Also, this would also explain why the air temp was warmer while sitting at idle, higher engine compartment temps....

Second, yes the heater trick works real well....On my 82 I would have to switch on the heater on REALLY hot days to keep the truck from overheating....ya know, those are the days your REALLY didn't want the heater on, LOL....Also had to do that a couple of time on the wifes 65 mustang....Seems like it would bring the water temp down 15-20 degrees....

[TIMSPEED]

Originally posted by allthrtl
First, change the thermostat, either way, it probably needs it...I'm not positive how it works on these trucks, but you also want to check and make sure the door in the vent system is opening and closing properly, you can hear it when you adjust the temp selector(cool<--->hot)...If it's not working, then air isn't going thru the heater core and therefor isn't going to be warm...Also, this would also explain why the air temp was warmer while sitting at idle, higher engine compartment temps

First off, the thermostat is brand new.
Second, I think I will check that temp selector door (cool<--->hot) door. I visually checked the defroster door, and THAT'S working, but I'll have to take the heater casing apart to see if the cool/hot door is working. It prolly isn't. I really won't have to worry about it till november though

[Blue Beard]

Just replace the diverter box on mine for the same reason......

if you find you need to replace, check out:

http://www.gmpartsdirect.com
http://www.partsonline.com

[apstguy]

You don't need to take it apart, just listen for a thump when you move the selector back & forth. I don't know about yours, but it takes a little effort to move the selector from hot to cold and vice versa. If it easily slides, then it is broken. Do you have A/C? On mine, if you take of the main distribution duct, you can look into the box and see the evap. core and you can see the hot-cold door.

[1FaastC10]

Originally posted by TIMSPEED

First off, the thermostat is brand new.

new doesnt always mean good. i've had several AC Delco thermostats that were bad right out of the box.

[Grim Reaper]

Make sure you have it plumbed correctly. If you have it plumbed wrong it can trap air in the core. Propper plumbing is from the INTAKE with 5/8's hose to the bottom inlet on the heater core. If the water is coming from anywhere but the intake your getting return water from the radiator.
The return comes off the the top line in 3/4 hose to either the top of the water pump or to the radiator.
Properly plumbed and the blend door working correctly you should have decent heat even with a 165deg thermostat.
The blend door is the one on the top of the box that is visable with the glove box door out.

Here is a write up I did on heater core replacement.
http://coloradok5.com/heatercore.shtml

[ElGracho]

Originally posted by TIMSPEED
...I parked for a few minutes in taco bell parking lot, and after a few minutes of idling, the air got a little hotter. ALSO, I thought my coolant temp guage was broken..turns out, it's NOT! My truck just DOESN'T get warm AT ALL.

This statement above is the key. I doubt if there is anything wrong with the heater core. For some reason, coolant is not being regulated by the thermostat to let the engine get up to temp and stay there. When you shut off the engine, the cooling from the radiator goes away, all of the heat convects to the top of the engine and your heater is hot when you first start it up because of this. When you start the engine and start driving, the radiator cools the coolant back down again and the heater cools off. Check the thermostat, it's not working, as evidenced by your temp gage.

[TIMSPEED]

I actually think my temp door is busted, because when I go from cool to hot, it's too easy and I don't hear anything.

[the baron]

Just put it in a with water filled pan on the stove , heat on.
When the water reaches the boiling point , the thermostat has to open slowly.
Goes it open a while before your water is at boiling temperature ( let's say , @ 100 °F ) , is your thermostat toast...
Does it not open at boiling temperature , is your thermostat toast also, but don't be surprised when your engine turns from a gas engine to a steam one
I had to put a new thermostat in my Impala , as the water temp won't rise : there was no thermostat at all...
Before I've put the new thermostat in the engine , I did the test.
No problem at all...

The Baron
____________________________________________________
1979 C10 LWB , 350 Oldsmobile engine , rusty stock
1977 Impala sedan , 250ci , "Ye Old reliable"
1960 Girl friend , frame still good , body has some dents

[PHOENIX]

My truck is non A/C model.
My heater door is very easy to activate and doesnt make a sound when done with the switch (control panel, by cable system, no vacuum). If you grab the little lever that the cable attaches to (NOT at the control panel) and shift it real hard (kind of fast and jerky ) then you should hear the slight thunk. I believe there is a small peice of foam glued on from the factory that helps seal and allows a quit shutting of the door. I would check that way before taking it apart and checking it out. I would suspect that your thermostat is ok, but a higher opening temp. would increase your cab heating.