I have a 99 Dodge Cummins and the heater doesn't get very warm. I've replaced the thermostat, the engine runs at 185-190 degrees. The heater hoses are warm to the touch. When the pickup is warm and just idling, the heater seems warmer, but when you go down the road it's cooler. Turn the fan on hi and it's cooler yet. Is there a heater valve on this engine? I can't find anything, and sure hate to start tearing apart the dashboard, etc.. I'd sure appreciate any suggestions.

 

I have the same problem I'd like to know as well

 

The coolant out fitting on the top of the head going to the heater core has a small inner diameter. A lot of guys drill them out to allow more flow, or you can replace the fitting with a regular pipe to barbed fitting.

One thing I do before it get too cold out is a reverse flush. Either drain the coolant or pinch off the lines at the heater core. Then using a garden hose with HOT water, flush the heater core both directions twice for about 15 seconds each time. Alternate back and forth. This will flush out the internals of the heater core, allowing more coolant flow and more heat.

 

Many thanks! I'll give it a try!