I have a 1989 dodge ram D-350 single wheel long bed, 12 valve non inter-cooled of course, with the 3 speed auto trans, I can't find the spec for the running temp.

Also when I get over 45 mph I feel a vibration I think is in the rear, I changed the u joints, checked the diff fluid, rear wheel bearings, brakes blah blah etc etc and still does it. It got better after I did all that but it is still there. If anyone could help it would be appreciated thanks.

 

Thermostats open around 181, anywhere between that and about 205 should be fine. Just running around without a load with everything in fair condition 185/195 would be reasonable figure.
The accuracy of your gauge may need checking if you have doubts

 

I did hear that. But I was looking on a forum the other day and they said there's doesn't run over 170, 180 if towing. Of course that was an intercooled motor.. Which is why I was asking my truck in 110 degree weather with the a/c on it gets up to 192 and stays steady, cools down if anything... I have an aftermarket gauge to be 100% sure. Anyway thank you for the response greatly appreciated!

 

Have the driveline rebalanced. Ive seen alot of trucks that need it. Heck mine looked like a banana I guess when it was shortened for the 47rh.

 

If you have removed the rear wheels lately and didn't get them centered on the axle when reinstalled, it will vibrate.