I can't help you with the heads question, but had to say HI to another Isuzu TD P'up owner.
I have never seen one of these things on the road except for my own, but yours is the 3rd one I have encountered on MercedesShop forums.
From your user name, it sounds like you must be using some kind of cooking oil in yours?
2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg
And remember folks, Only You Can Prevent Hilliary.