I don't seem to see anything that resembles a pump under the turbo area. I have an aux. pump at the firewall just to the right of the monovalve contraption. At least I think it's an aux. pump. It has several hoses connected to it and when I turn the heat system on max this little doo-dad kicks on. I assume that it is working alright. I may just order a new monovale insert to see if it helps since they are not too high priced.

I am also going to replace the t-stat tomorrow just to see if that makes a difference.

Are there not two temp sending units on the head of this 300SD?
Just thought I would ask.

Kevin