Re: Which is the BEST synthetic oil? O.K. to pour into flathead


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Posted by David Sherman [216.18.131.157] on Thursday, December 31, 2009 at 04:13:31 :

In Reply to: Re: Which is the BEST synthetic oil? O.K. to pour into flathead posted by The Dodge Boys [205.188.116.76] on Wednesday, December 30, 2009 at 23:45:23 :

This is an interesting discussion. If we're just talking about which is the best synthetic, I'll defer to those who have tried some, but if we're talking about whether synthetic is better than dino juice, I can think of arguments both ways. In favor of synthetic, it's supposed to provide better lubricity throughout its long life, maintain its viscosity better over temperature, and generally do all the oily things better. In favor of dino juice, today's cheapest multiweight service grade SF or whatever they're up to now is clearly better oil than WWII's 30 weight in the summer, 10 weight in the winter, and diluted with kerosene or gasoline when it gets seriously cold. Heck, it might even be better than WWII synthetic.

It seems like many of the advantage of a synthetic would be lost on our old trucks. The synthetic may hold up better under extremes of high temperature and high pressures, but those conditions aren't encountered in an old flathead. In a truck that's rarely driven, it seems to me that condensation in the crankcase, water and acid from cold starts and short trips, and rusting of cylinder walls and rings due to oil draining off of them while it's parked are going to be the real causes of excessive wear, and I'm not sure that synthetic is any better at dealing with those problems. Water with oil in it is bad no matter what the type of oil is, and if oil drains off of engine innards and moisture condenses on them, it doesn't matter what kind of oil is sitting in the sump. On the other hand, maybe synthetic oil sticks to the cylinder walls longer and resists breakdown from acid and water better than dino oil. I wouldn't want to just assume that, though.

It does seem like the conditions in an old flathead, infrequently driven, are quite different from what synthetic is designed for -- high-performance modern engines driven hard.



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