Originally posted by LarryBible
The problem with 20W50 is the fact that there is an inordinate volume of an additive called "Viscosity Index Improver" added to the oil to make a 30 weight spread from 20 to 50. This amount of VI additive is known for causing excessive "coking" or carbon buildup, particularly in smaller, hard working engines such as yours.
If I may...the problem with the V-1 modifyer was limited to 10W40 oil. GM study done in the early eighties...Volvo voiding warranties if it was used...etc..
Since 20w50 starts with a base that is twice as thick as 10w40, the problem doesn't show up. I doubt there is a name brand oil maker on the planet that still makes the "evil brew" that caused the problems.
Back to the question at hand, I don't think you would have a problem using 20w50 oil, but consider the switch to Mobil-1 15w50 and run regular oil changes instead of short-cycle 3K mile changes. I use 15W50 all year in everything I have, and it gets really cold up here Really
. But then, when it's 20 below zero, nobody "has" to go anywhere do they.