Heater problems?

[81ChevyC10inSC]

Ok i have 81 C10 w/o AC and the i6 (250). Bought the truck some time ago and have had issues with the heater ever since. Hadnt worried about it much until the colder weather got here. The truck has what appears to be a brand new radiator. I have replaced the heater core (old one leaked) thinking that would fix my problem. It didn't. So yesterday I replaced the thermostat (195 degree) just in case and topped off the coolant. Let the truck idle to get up to temp and I had really good heat. Weird thing was only the hoses going to the heater got hot. Neither top nor bottom hose to radiator got hot.

So this morning I start it in the drive way and let it idle for 10-15 minutes. I get in a notice no real heat yet. So I drive in to work (30 minutes but only because of traffic) and still only cool air is blowing from defrost or heat. With it running I checked under the hood we I got to work and had zero leaks and all hoses are hot. I really am at a loss at this point on what to check. Could I have an air bubble maybe?

Any ideas or suggestions would be greatly appreciated

[geezer#99]

Do you have your hoses on right?
Got a pic?

[81ChevyC10inSC]

Originally Posted by geezer#99

Do you have your hoses on right?
Got a pic?

I feel I have them on correctly but I will try to get a pic. One to the water pump and one to the intake.

[Malibuick231]

Is there a valve in the heater hose that isn't working properly?

[geezer#99]

Originally Posted by 81ChevyC10inSC

I feel I have them on correctly but I will try to get a pic. One to the water pump and one to the intake.

One from the thermo housing to bottom port on the core and top of core back to water pump.

[motornut]

are you able to move the air with your controls?
depending on the coolant ratio/water mix it can even ice up.
is the rad the right size?

[Dead Parrot]

Having just replaced my heater core, make sure your cable to the hot/cold flapper didn't pop loose or the adjustment screw for that cable didn't loosen. Since it worked once, guessing the problem is either an air bubble or the hot/cold flapper not working.

My return heater hose dumps into the radiator by the cap making it easy to verify coolant flow. It only took a few seconds of mild engine reving to force the air out.

It is possible the reason your radiator hoses stayed cool during your first idle test is the heater core sucked enough heat from the engine to keep the thermostat closed.

Don't overlook the possibility that your new thermostat has suck open. I had one fail after two months.

[81ChevyC10inSC]

Originally Posted by geezer#99

One from the thermo housing to bottom port on the core and top of core back to water pump.

thats how they are hooked up.

[81ChevyC10inSC]

Originally Posted by motornut

are you able to move the air with your controls?
depending on the coolant ratio/water mix it can even ice up.
is the rad the right size?

I can switch from defrost to heater and the air moves with the change. Also the coolant mix is 50/50. Usually doesn't get overly cold in South Carolina.

As for the radiator im not sure. Is it possible to have to have one that is too big?

[81ChevyC10inSC]

OK New symptom. I drove all the way home and realized all the hoses are hot except for the bottom radiator hose. The bottom hose isnt even warm at all. Could the water pump be the problem? could i have a circulation problem? Radiator Cap maybe bad?

The engine temp gauge never got above the 1st line in the summer and doesnt reach that since its turned cooler. So its seems the engine isnt over heating at all. This just has me stumped.

[bnoon]

Originally Posted by 81ChevyC10inSC

I can switch from defrost to heater and the air moves with the change.

There are two air diversion doors in the system. One controls where the air comes out (vent/floor/defrost), and the other separate door controls the temperature of the air comes in (either cooler air through the vent or warmed air that comes through the heater core). You can open your glove box door and see if the little wire moves the temperature select diversion door near the gap at the top left section of the open glove box. If that diversion door is stuck to one position vs. the other, you will not get heat.

If the heater hoses are getting hot, I'll bet the temperature select is your issue. If not, pull one hose from the heater core and verify you get flow when the engine is cranked over.

[bnoon]

And just FYI reference, I just had to troubleshoot my heater in Mr. Green Jeans. I used my big 4 core radiator from the 454 truck and the return was in the radiator instead of the intake. I used the port on the back of the water pump for the feed and that was wrong. I had to move to another port on the new intake before I got adequate flow. Now I have very very good and very VERy quick heat and the temp needle BARELY gets to the lowest quarter line.

Bottom line, your heater lines are hot = hot heater core. Look elsewhere for your issue.

[81ChevyC10inSC]

Originally Posted by bnoon

There are two air diversion doors in the system. One controls where the air comes out (vent/floor/defrost), and the other separate door controls the temperature of the air comes in (either cooler air through the vent or warmed air that comes through the heater core). You can open your glove box door and see if the little wire moves the temperature select diversion door near the gap at the top left section of the open glove box. If that diversion door is stuck to one position vs. the other, you will not get heat.

If the heater hoses are getting hot, I'll bet the temperature select is your issue. If not, pull one hose from the heater core and verify you get flow when the engine is cranked over.

I will give it a try when i can as its not overly cold yet but was trying to get ahead of the problem. So probably wont be able to do the hose check till this weekend but i will try the check the temperature select tomorrow or later tonight. Thanks for the help.

[Just call me Sean]

Originally Posted by 81ChevyC10inSC

I feel I have them on correctly but I will try to get a pic. One to the water pump and one to the intake.

Originally Posted by geezer#99

One from the thermo housing to bottom port on the core and top of core back to water pump.

Originally Posted by 81ChevyC10inSC

thats how they are hooked up.

Well, which way do you have them hooked up? Because that's two different ways. Intake and water pump or intake and radiator, not the thermostat housing.

[geezer#99]

Originally Posted by Just call me Sean

Well, which way do you have them hooked up? Because that's two different ways. Intake and water pump or intake and radiator, not the thermostat housing.

He has a 250 six banger. Bottom hose to the heater core comes from the thermo housing on the front of the head!

[Just call me Sean]

Didn't notice it was the six, and I don't know those. So I defer to the more knowledgeable.