Is it OK to change to synthetic on a motor with 160K? Is there any preparation?

 

what about going to synthetic on a motor with 160K? Is there anything that needs to be done to prep the motor?

 

Bad idea. All of the small leaks that have sealed themselves with gunk from the old motor oil can/will dislodge. At the minimum leaks will spring up everywhere and your engine will smoke as the oil gets passed the rings. At the worst you'll toast the motor when oil passageways get plugged.

It's got synthetic from the factory.

 

How about the rear end?

 

Yes, that would be okay, but if regular dino juice held up for 160K, why bother switching. Also, has the diff fluid been changed before? However, I wouldn't be surprised if you get some whining after the fluid change, especially if you go with a lighter weight oil.

 

If you do opt to go with synthetic, you would be smart to do a serious cleaning of the engine internals first. One, to prevent the above mentioned plugging, and 2, the synthetic will most likely do a very rapid cleaning and hence plugging of the oil passages.Plus, why waste the very expensive synthetic just for cleaning purposes. What doc says about the little leaks springing up all over often holds true also. Such as the oil pan front and rear seals, front cover seal. The engine can be cleaned up with a regimen of "Seafoam" treatment in the oil just prior to changing, but I would do several short mileage changes before you switch, and run the Seafoam through it just before you change the oil each time.
At this point in the mileage, you might be better off to stay with the Dino oil.