Originally Posted By: Astro14
I don't think of your engine as "old" or "vintage"...
But there were a couple of interesting schools of thought many years ago.
1st was that you should never run a detergent oil in an engine that was run on ND oil...many truly vintage (30s and earlier) owners had problems with all that sludge coming loose...correlation? causality? Who knows...it was thought to be so (discussed with the engine builder when the Packard's engine came out in 1976).
2nd was that (and you'll laugh) that the Non-detergent oil was more "pure" and lubricated better because it had no additives, just oil...
3rd was that any multi-grade caused sludge (and back in the day, VI chemistry might have been the cause...or it might have been the incredible carbon build-up, fuel dilution, and NOx blowby from those old engines that used to be changed out with every season when using mono-grade...that then started to really build up in the multi-grade that was run for a longer OCI)
So, I suspect that your engine, though I wouldn't call it genuinely vintage, has been the victim of these old ways of thinking. I would run very short intervals with a good conventional oil...and keep a close eye on the oil pressure...
Most of the sludge will probably be in the bottom of the oil pan...if it were mine, I would pull and clean the pan...the galleries are likely OK...
One more thought as well - way back in my teenage days, (late '70's) a lot of the old timers I knew who worked on motors believed that a rebuilt motor had to be broken in on non-detergent motor oil. Their thinking was it washed out all the metal shavings and helped the rings seat better as the additives would "get in the way" of the rings trying to seat. They would run non-detergent 30 weight for 500 miles, then change it to a detergent oil. These "old timers" were in their 60's in the mid to late '70's, so their experience dates back to the '30's and '40's. Perhaps, the "Dad" who rebuilt the OP's 350 learned the same thing and somewhere along the way the info got mixed up and later owners kept running non-detergent - just guessing here, but I think you're probably right about the 30 weight mentality. I'm a big straight weight fan myself.
