Okay, I'm having heater troubles in my Dak as well. According to the temp guage though, the engine isn't even reaching normal operating temperature. So, I was going to try to replace the thermostat to see if that was the problem. Only trouble is, can't seem to locate the thermostat on the 3.9L engine. Are they the two things mounted on the top of the cylinder heads? I always thought the thermostat was a single part, mounted near the intake manifold. How high does the engine temperature need to be for the heater to work, anyway?

 

Just follow the rad hose to the front center of the intake uptop and that is the thermostat. I would also look into a new clutch fan too as that was my problem, only running 1/4 on the temp needle, when everyone else I know their temp runs about half way. I have read that the clutch fans go in these trucks. For me it was an $80 canadian part, so even cheaper for you US guys.