I run Mobil 15w50. No leak problems from the oil heat exchanger. 

I don't think I would run 10w40 oil except in the bitter cold of winter. 

Chris.

Wysłane z iPhone'a

Dnia May 25, 2011 o godz. 22:40 Max Wellhouse <dimwittedmoose@CFU.NET> napisał(a):

> FWIW, I had been running Mobil 1 in the engine since  5k after its
> rebirth, but I've had several instances where the Oring seal  at the
> oil cooler was leaking.  It was doing it again last winter and into
> the spring, until I changed oil and returned to Castol High mileage
> 10/40 oil.  The leak, if not totally stopped, is much, much less for sure.
> 
> Since the O ring seal is black and presumably not Viton, and since
> full synthetics love/demand Viton seals, could this be a coincidence,
> or something more??
> 
> Does such a thing as a Viton Oil cooler seal exist??  An argument
> could be made that the oil filter seal is not Viton and normally
> doesn't leak, but I am at a loss to explain this in another logical fashion.
> 
> TIA
> 
> DM&FS