[77newell]

Since I've owned this 93 coach the dash heat has been pathetic, barely keeping us comfortable when it's less than 55 outside.

I changed the boost pump due to a noisy bearing - no change in heat output.

I overhauled the solenoid valve at the inlet to the pump - no change in heat output.

While finishing the solenoid overhaul I noticed that the engine coolant shutoff valve feeding the pump and solenoid didn't make nearly as many rotations before it came to a stop. I had operated this valve in the past but never noticed the small number of rotations until it came to a stop. I then could feel that the stem wasn't extended nearly as far as the other valve - can't see the stem due to location. In attempting to remove the handwheel I discovered that by tapping the bottom of the handwheel with a small hammer the valve would open a few more turns. After many iterations of this the stem appeared to match the extension of the other shutoff valves. I now have real heat.

[ccjohnson]

Sounds like some scale build up. You may be due for a cooling system flush & coolant replacement.

[Fulltiming]

Good catch. A reduced flow of hot water will certainly reduce your dash heat.