Intermittent Heat Issue

[matt204]

Hello everyone

When I'm driving down the highway my heater starts to blow cold quite often as soon as the truck gets to a coasting speed but under any slight acceleration it starts blowing great heat. Its not losing coolant and level is just under the min mark as its supposed to be. Could it be the heater control valve? if I unplug the vacuum line will that do anything? Any other ideas?

[fatdoug]

mine was doing the same thing, and my coolant was at a similar lvl, all i did was cover my grill and added about a 1L of coolant, now she blows nice and hot all the time. hope this helps.