heat issue

[fatdoug]

so its started to get cold -20 celsius and i'm sick of being cold, when the truck is stationary at idle/warming up, blows heat no problem. once im driving her and she gets up to operating temp (thermostat opening), the heat stops blowing, actually get's as cold as ambient temp. so far i have checked degas for coolant level and any signs of head gasket/egr issuse, everything is looking peachy also no signs of vacuum leaks (auto 4x4 works). my thoughts are, i need to block off more of my grill. maybe a flow problem to the heater core or maybe the airflow over the heater core. any thought or opinions would be greatly appreciated.

[kinnisoj]

Juz takin a shot in the dark but if it was my truck Id do the easy things first and change of the T-stat.

[Ron-M]

Is the heater valve open? Does the hose to the heater and the return, lower hose under the degas tank, get hot?

[twoicebergs]

We are having the heat wave here the past few days, 0-2*C, getting cold again tonight - thanks for sending the weather our way!

Has it done this since you have owned it or just this year? I have never had a heat problem, except for the excess heat in auto mode while the back of the truck heats up.

Do you have the heater in manual mode or automatic? It probably doesn't matter, but as you may have noticed, when the truck heat gets up to almost normal the valve opens to let more water circulate to the heater core and then the fan blows strong. I'm guessing here, but perhaps the valve is closing for some unknown reason or the electronic controls are screwing up? Most of the heat problems tend to be from not ever getting warm enough; clogged core, vacuum or switch for the CC, thermostat, and finally the heat management system. Can you select full fan, or does it stop as well?