Quote:
Originally Posted by nickmckinney
The tolerances and clearances are no different than the pushrod motors they replaced.
One version being speced for 20W and another for 50W and they have the same clearances internally with many of the same parts should tell you that you can run any viscosity you want in these motors.
The thicker the oil the happier the cam bores, the thinner the oil the happier the cold start gas mileage is what I have seen.
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In my 1970 Mach with 351C-4V I use Shell ROTELLA T Multigrade SAE 15W-40. The diesel oil seems to be the preferrred oil for old Muscle Cars. It has the zinc that is still required by the older OHV designed engines. I change it twice a year and it usually only has about 1500 to 2000 miles on it but it's very cheap and each oil change is done by me for around $20 total.