[VACList] Tow vehicle oil viscosity question

["Mr. Joy H. Hansen" <joytbrew@xxxxxxxxxxx>]

Hi All,

My brother just purchased a 1 ton Ford van to haul his family (seven kids)
around.  As he prepared the new purchase for a vacation, he purchased 4-40
Rotella synthetic as it was on sale for half price and he tends to keep his
vehicles for 10 years or 300K miles (which ever comes first).  He drained
the old oil and moved on to replacement.  That's when he noticed the
recommended oil viscosity on the cap of the filler tube.  A manual didn't
come with this preowned vehicle.  Anyway, the recommended viscosity is 5-20!
Some thoughts are that this light weight is only for increased fuel economy
without regard to engine longevity.

The local Ford dealership tells me that the oil galleys and machine
clearances won't tolerate higher viscosity.

Any actual experiences with the Vortec V8 would be much appreciated.

                                                    '69 Safari, Joy