91’ 740 turbo 4 door. From what I know it has always used regular old oil. It has about 140k on it now, and I was thinking of making the switch to synthetic oil. Do I need to do anything to the engine before I do this, and is it a good idea? Thanks a lot.

 

G'day mate. I've heard that with the older cars-if you've always used fossil based lubricants, continue to use them. Apparently, if you change to synthetic oils which I heard are thinner and have detergents you could clean out all the slug which is actually acting as a bung and your car could start leaking oil. I don't know for sure though. Just my two cents worth.

 

That is what everyone says. Some cars leak oil worse from where they already leak.

You will be fine installing it.

 

mobil 1 10W-30 syn.....thats what im running, would recommend

 

I have found the "high mileage" formulas a real benefit to the nagging leaks
that 200+K have to live with. I did indeed find higher loss with Mobil 1 and
have been using Pennzoil High Milegae since and my driveway loves it. If you
change oil every 3-4K, M1 is all of throwing money in a drain bucket.