I've got a 96 Ram 2500 with the 5.9 Gas engine. I've noticed that if the fan is on low, there's lots of heat, but as I increase the fan speed, the heat goes away. Is this a sign of a possible clogged heater core? I'm thinking that maybe the core is plugged and not letting enough flow go through, so as the air flows past it faster, it doesn't pick up enough heat.
Anybody else have any ideas.


Water pump is fairly new and I've got a 195 thermostat in there.

 

Its probably a partially plugged heater core. Try back flushing the heater core and see if that helps.

 

Or you have an air bubble in there. Backflushing should take care of that as well, just try and leave as much water in the lines as you can when you put the hoses back on.