[brownbear]

with your probe on the injector the temp at 25 degrees(running only diesel un heated) is because heat is tranferring from the head up the injector line. When it is running the cold diesel keeps it at 25 degrees. But I think the IP will be hot enough that some of the 25 degrees is from the warm oil in the IP. When your shut down the cool diesel is not flowing and taking away the heat from the head. Hence why it is hotter when you first turned it on.

When your running warmed veg oil I would like to hear the temp at this injector. My thinking is it might not be too much different. But lets hope it is.