Does anyone run or tested synthetic oil in flathead?What is the good,bad and ugly of this idea?

 

You're probably fine running synthetic. If you have leaks, it will leak a little worse with synthetic.

Your best bet might be to use a diesel rated oil like Shell Rotella 5W40, Mobil 1 Turbo Diesel 5W40, Delvac 1 5W40 or similar.

Rotella 5w40 is available at Walmart for about $16 per gallon.


Cheers,



Rick