We have found on my D90, during any load on the electrial system the temp gauge would climb almost into the red. Once we removed the load (ie, turn off ac & lights) the temp indication would immediately drop down closer to normal. I have just done a top end overhaul on the engine. All new headgasket kit, waterpump, clutch fan, electric ac fan (original was locked-up), hoses, rocker arm assembly, & temp sensor. I had thought my over temp indication before the overhaul was due to a head gasket leak. Then shortly after I was done the indication returned. We bled all the air out of the coolant system, but it continued. It finally returned to normal once I installed a bonding jumped to the bock, body, & frame.
The problem with the crank getting magnetized might not be as bad as we thought. The compas method might be to sensitive. I am going to try to use some metal filings and see if the center pully bolt on the crank will attract them. If it is strong enough to then, I will need to de-magnetize the crank. We have been talking on how to do that just in case. I'll let you know what we find out. Thanks, I hope some of this has helped. J.W.