I have a question that I am hoping someone can help me with. I have a 1979 Ford F250 with a 460 J-Type engine.
Recently the heater has become intermittent. I removed the old thermostat and replaced it with a new one. I checked the old one (180 degree) and it was still good but replaced it with a new one (190 degree) anyway.
The new thermostat did not correct the problem. I thought it might be the heater core, but nobody seems to think that a heater core can be intermittent.
The truck warms up nicely, no overtemp issues, the coolant level is good. To compond the confusion, In the morning I start the truck and after about 10 minutes, it blows warm air. As soon as I put it in drive, nothing but cold. If I put it in park, it may blow warm, it may blow cold.
My brain has me thinking it could be a vacuum issue. I am going to change the heater core regardless but thought you guys might have some good ideas for me.