A little thread creep on a near subject. After a recent coolant drain and re-fill with CDL coolant I had the bus out this past weekend. I ran the webasto for 30-40 minutes on two mornings. When I got ready to head home the dreaded check engine light was on red. I checked oil, transmission fluid and made my way to the engine water holding tank. Luckily I had three gallons of the new antifreeze on board and it took all three to fill the system. Evidently the webasto water system had a huge bubble in it that did not show up until I ran it. We ran the engine on the road after the coolant change and added more fluid. I even ran the webasto for a short spell at that time and the bubble stayed in the system until this later date. All ended well.
Brian I think you have the answer to your Gen Set scoped out. Good Luck.
Harry
Shirley & Harry / 2000 Liberty / 2008 GMC Envoy Denali