Hello. I've got a 1990 F70. I put a TD lump in there 2 weeks ago to replace the original NA engine. Everythings been going fine, until today. I did my first bit of motorway driving today, 140miles. I only go 60mph, but the temp gauge went up past its normal half-way mark to about 3/4. At one point it went up to just below the read, for apparently no reason. Then it went back to between 1/2 and 3/4. I didn't change speed during this time, and the motorway stayed flat, so I was thinking possible temp sender trouble? BUT, it does go down to normal 1/2 when I coast down hills, so something is working as it should. I took the stat out and gave went down the motorway again and it still went to just under 3/4.
Next step is to remove and pressure was the rad, it is muddy, but you can still see through it.
Oh, I flushed the cooling system out when I changed the engine.
The only other thing I can think of is that the rad is blocked on the inside, but it didn't overheat this badly with the NA in, but this could be because the NA engine runs cooler anyway than the TD?

Does the TD Fourtrak have the same sized rad? I compared mine to the one from the donor 'trak, and they appeared the same...

So, can anyone give me any ideas/help as to whats going on? Also, what temp do your TD 'traks run at on the motorway? 1/2 on the gauge, more?

Thanks for your help, really want to get this solved asap,

Ben