#745 had a very similar problem when it was started up in Sep 07. There is a thread here .. a lot of the same suggestions were made. You know what it was? The
oil temp probe and the water temp probe look identical from the engine side of the firewall.
I had the oil temp probe screwed into the intake manifold and the water temp probe screwed into the oil pan. As the engine warmed up, I had a nice 180 deg oil temp, but a wildly fluctuating 220-250 water temp!
So just do a quick check on that as well
Sam