My son has a 1989 chevy shortbed, 350, 4X4. The heater is not heating. What can I look for to fix this problem? You should know that the A/C does not cool either, in case it might be related.

 

Are the two hoses going into and out of the heater core hot? If not I would consider that possibly the heater core is plugged up. If I am remembering correctly, I don't think that vehicle has a water control valve that controls hot coolant flow into the heater core.
The A/C issue is most likely a seperate issue. I am assuming your HVAC blower motor and air handling system is working correctly. If not it sure would affect A/C and heater output.

 

Thanks for your reply. The blower appears to be working fine as it is blowing cold air very well! I pulled the Chilton out to locate what I need to check. When the truck is available to me again I will check the hoses to see if they are hot as you suggested. I will proceed from there.

 

Julie, something else to look at. Check the coolant level with the engine cold. Low coolant can affect heater performance. Is the temperature gauge reading normal? I have seen air in cooling systems cause the issue you have. Sometimes this air is caused by a blown head gasket. These are just additional things to think about. Keep us posted!

 

We just replaced the head gasket etc. As the oil and water didn't mix when they met. Whatever the complete gasket kit contains. I paid someone to do the replacement gaskets. He checked the heads and they were not warped. Haven't had anymore issues with the coolant and oil mixing. Is there something that might have been left undone during the work that could be causing my current problem? The thermostat was replaced several months ago as well, and the temperature gauge appears to be working normal. The coolant level is good.

 

I can't think of anything more to tell you. Do the checks mentioned in my first reply and we'll go from there. From what you tell me I would not suspect any problems resulting from the headgasket repair.

 

In doing a head gasket replacement, when you put new intake gaskets they have block off plates on the gaskets that need to be removed or left in place depending on where the heater hose is connected, in other words some trucks heater hose connects to the back of the intake and some to the water pump, if this truck hooks to the back of the intake and the intake gaskets had the block off plates on them than the water isnt flowing into the heater hoses causing no water to get to the heater core meaning no heat, but do the checks mentioned in the other replies and go from there

 

Hey j400, that's something to consider if the heater hoses don't get hot as mentioned in my first post. I think the next step a person would then take is remove the hose and confirm that coolant flow is there. It sounds like that slip-up could easily happen if a person wasn't paying attention!

 

When I bought my 1993 K1500, I had the same problem. Turned out that someone had used stop leak or some other gunk and it stopped up the heater core. Release the return line under the hood, as well as the supply line and force fresh water from a garden hose through the return line. You will see an inordinate amount of crap come out of the supply line. Heated fine after that.