Truck has heat when driving but when stopped blows cold air. Replaced thermostadt. still blows cold when stopped any ideas
Try purging any air out of the cooling system.
To do this, get the engine up to operating temperature. With the engine idling, lossen the upper radiator hose clamp and insert a small flat bladded screwdriver in between the radiator hose and the radiator hose neck. Allow the engine to idle until all the air is purged from the cooling system, or until hot air starts coming out the vents. Remove the screwdriver and tighten the hose clamp.
Good idea above. Also feel the coolant hoses that go through the firewall. If one hose is very hot, yet you are getting no heat, there must be something wrong with the flow of hot coolant through the heat exchanger (which is the source of the heat) under the dash, or the car’s venting system and doors. There’s also a possibility the new thermostat isn’t working either. Did you put it in a pan of heated water with a thermometer and make sure it opens at the correct temp? Did you make sure to position the thermostat correctly? There’s an up/down orientation on most thermostats, as well as an inside/outside. & make sure the belt which drives the water pump is in good shape, isn’t slipping, and adjusted to the correct tension.
Check the radiator antifreeze/coolant level. It’s probably low. If it is, then you should look for leaks in the coolant system. I had this exact same problem with my s-10 and there was a leak in the heater outlet pipe (small metal pipe, going towards the back of the engine, that connects to the thermostat housing). This may not be the same leak that you might have, but that’s a spot to check.
For crying out loud Sean do you really think after 3 months they haven’t solved their problem or gave up?
Some guys are reviving threads that are a year old . . .