Hmmm. I think 52~57 era Chevy's also calls for the 10w 30, and 5w 30(if avaible) for the yearlong... Also the '57 Studebaker calls those 5w 30 specs in the user manuals if memory serves right. It was interesting for me to discover that 5w 30 was avaible at the 50's. So analogy repeats: this might not be related with the clearances. In 50's o-rings may not be made of the molibdenum alloys so I expect a different mechanic design there. But 5w 30 viscosity seemingly very long lived. I wonder why...quote:
Originally posted by Jimbo:
This SAE 20 thing is not new at all. American cars from the 1950's used it. The owners manual for my 1957 Chevy calls for 20W-20 as the primary recommendation. The heavier wieghts really became popular in the '70s due to the higher temperatures in emission-controlled engines.
One more thing is that my Chevy V6 clearly states not to use anything heavier than SAE 30. This one also indicated on the orig. service manuals. Be it the '52 Chevy or the an '89 V6 they say use 30w if you can't find a multiviscosity. So Straight 30 is better than a modern 10w 40? (One thing draws my attention is that all these engines have hydraulic pushrods.)
On the other side 70's European Ford manuals say OK for almost any viscosity from 5w 30 to 20w 50.
Appearantly there are engines that go to a ban for some viscosities and there are engines says OK for whatever the viscosity is. Here (in Turkey) 20w 50 called asa rule of thumb for the many years. (Unlike the popular idea it is not that hot down here. Last week it was still snowing.)
Jimbo, it is nice to meet a "collective mind"