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- - Heat? (https://67-72chevytrucks.com/vboard/showthread.php?t=719291)

Alright.. This seems to be an on going thing for me due to the winter weather.. I have replaced the heater core about 3 months ago, the thermostat around the same time and just replaced the radiator on presidents day.. The heat is nuke warm and when I drive it gets a little better and cools down when I stop.. There is a possibility that air is in the heater core lines I understand that but, then why would the temp go up and down while I'm driving? Could this be a water pump issue all this time? how do you know it its bad? I don't hear any whining noises or such.. Thanks, Mike

I don't think the water pump is the issue. Its doing its job of cooling your engine. If it ain't broke, don't fix it. A bad water pump will either make noise if a bearing is going out on the impellor shaft, or it will leak coolant out of the tell tale hole located on the underside of the pump housing. The tell tale hole is designed to let you know when seals are going out in the pump before it has a catastrophic failure.

Air can certainly get trapped in a new heater core. When I did mine a while back, I installed a coolant flush kit "T" fitting in the top heater core line. When I added new coolant to the radiator, I kept the cap off of the fitting to let all air pockets in the heater core below the fitting come out of the system. I then closed the cap and performed a standard burping procedure with the radiator.

Also, check the heater core inlet and outlet bungs on the radiator for blockages. If either one is partially blocked with scale or rust, this will reduce the efficiency of the heater core.

New thermostats can be bad too. If the "new" stat has failed "open", the coolant won't reach full operating temp, hence luke warm heater core. I'd test the stat in boiling water to make sure it's opening and closing correctly.

does it have a clutch fan ?

no clutch fan.. electric fans on toggle.

Well, that eliminates the clutch fan as the problem, do you have a shroud around the fans?

no. but now I'm starting to think I might need to put on there..

Quote:

Originally Posted by GM man (Post 7731719)

No problem with my heater. Mine gets hotter than hell, so much so that I have to disconnect my heater core in the warmer months or my AC can't keep up. Sounds like you may have an issue with the valve that shuts down the coolant flow to your heater core. That's a cheap fix if that's what it is. Could also be your actuator doors aren't opening/closing completely inside your unit or sealing well, causing cooler air to mix with the air going through your heater core. Those are operated with vacuum, so I'd start with the little vacuum hoses and work back from there. It's all very straight forward and easy to work on.

dumb question, but have you checked the valve that goes to your heater core? the one under the hood, I can't think of anything else that could be causing you not to get any heat, like one poster said, remove thermostat and check it, it may be stuck open...