no heat

OK so i put a new water pump on and changed the thermostat my engine don't over heat but i don't have heat in cab when i drive down the road but when i sit still for a bit i have just a little bit of heat then it goes cold when i start to drive again what can be the problem now.

sounds like you got a bad tstat new doesnt mean its any good pull it out boil it in a pain of water make sure it opens all the way also make sure the giggle pin is up

I have encountered 3 different problems with the heating system in these trucks before. The first issue is that the linkage for the heater sometimes breaks and the lever doesn't move. All you have to do is to go down next to the heater core and move the knob. If the linkage doesn't move then there's your problem.


The second issue that I have seen is that the heater core can get clogged with rust over time. I found that a simple back flush works well to fix this issue.

The third issue is that the diverter valve in the heater core can break. Unfortunately this means that the heater core needs to come out and the valve replaced.


Pics provided courtesy of

yeah i had this problem too and the issue was the diverter valve. replace it and it works great.

Im having the problem of no heat. I have had to replace headgasket on my truck recently and truck is having good results but no heat. I bought the truck not running and am using it as my daily driver now. NO HEAT ROYALLY SUCKS THO. Can anyone give me a crash course on finding those cables or possibly a picture of it in the truck? I backflushed my system so that shouldnt be the problem. According to the picture the linkage is on the drivers side of heating unit. Im thinking about wiring it open if I can find it. Its 27 degrees here high this time of year and I need the gas mileage my truck gets so someone HELP.... LOL

Blower motor is on high and is blowing full blast but only cold air.

Hoses on both sided of heater core are hot and water rushes out when I pull the hose off.

What Emjay said and it may be the heater resistor.

so I checked the heat control knob and it was not fully open. After pushing it open by hand I drove truck 30 miles home and no heat again... How do I go about checking the resistor? I know where it is. I guess the next step is going to be pull the heater core and replace it and the diverter valve

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I've been catting through private message. Wow I forgot that I helped in this thread years ago, lol.
Don't feel bad, this is a common issue in these trucks.

How hard is it to pull the entire unit out if I need to replace it? I have never done it on this truck before but have on others but this looks like entire dash has to come out to get to it.

correct, the entire dash needs to be removed to access the heater core. the diverter valve is perfectly positioned on the heater core to make it IMPOSSIBLE to remove with the dash installed.

Quick test though before going through all of that, if you follow my flushing recommendation (from the PM) and water comes out of it easily, your diverter valve is open and not the culprit. If there is a lot of pressure and very little water comes out, then the diverter valve is closed.