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I just happened to get a pesky "video" today and it struck some cords from what the so called expert said, so I was refreshing the subject again of does W mean weight or winter and what about "no W" grades? Post war, we grew up calling "W" "weight" now it's "winter"... The (SAE) J300 viscosity specs were changed/updated in '93 and 2015, so even what was, is not now, by quite a bit. Instead of following the numbers as one would suspect, the viscosity is held constant and the test temperature is incrementally raised to give the low number value for W's. If it calls for a certain "old" grade in the owners manual, that would have to be translated to today's values over several updates. Lots of old oil was just straight one grade viscosity w/ or w/o detergent. Now we have multi-vis and loads of additives. I guess when it only cost a few cents a qt, no one paid much attention vs <$8 now. It gets more complicated all the time as they update and change formulae for new vehicles compared to the old standards. It's folly to think we're using the same fuels and lubes as the day it was born but we expect that same results, Einstein? There's plenty of paper proof of that. Similar at best, but not very. That can also be a good thing, if better materials. We also like to delude ourselves when we think we found the holy grail brand. It's a human nature thing. Once your brain decides that's all that counts, rightly or wrongly.

For what it is worth, here is an explanation in my brother's trade school book from back when oil was first invented! Naw, just 1968!

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I've had very good results running synthetic multi-grade oil in a Model T Ford.

I've driven it a lot, at higher speeds than it was designed to run at, in very hot weather, with no issues, using both 0W20 and 10W30 full synthetic oil.


Even very early Packards had better designed engines than the T Ford and by 1930, if not before, they had excellent engines with excellent lubrication systems.

In the 1930s, when SAE graded oil became available, Packard recommended a wide range of viscosity, or weight, oils, depending on expected operating temperatures. All carmakers recommend the use of high quality oil, regardless of viscosity.

Packard advised the use of SAE viscosity oils from 10W up to 40W, with lower visocity being indicated for colder weather operation.

Detergent oils were not available and neither were multi-grade oils until after WWII, and they did not become common until the mid to late 1950s.


Today, it's getting difficult to obtain a quality non-detergent oil, and single viscosity oils are becoming much less common.


The good news is that any good quality multi-viscosity detergent oil, whether "conventional" or "synthetic", will do a great job in any old engine that is in good condition and reasonabley free of heavy sludge.

Modern, multi-viscosity oils far exceed all required specfications for old engines.

Multi-viscosity oil does not need to be changed seasonally, and detergent oil will keep a clean engine clean, and will help clean up older engines that have some sludging and gumming issues.

For general use in most parts of the USA, a 10W30 or 10W40 oil is fine.

A worn engine running in hot weather might do better with a good 20W50.

If your engine is heavily sludged, you'd be well advised to clean it out, regardless of what oil you put in it.

At least remove the pan and clean it up and be sure the oil screen is clear.

Change the oil, any oil, if it becomes thickened or very dark or shows any evidence of suspended particles.

It's a good idea to have an oil filter on any engine, but it is not necessary to have an oil filter in order to use detergent oil.

This came up from another site and it's very long (1.5 hours) but very well researched/documented and typifies the progression of oils that causes the back migration I refer to.

youtube.com/watch?v=8oWFTOY-3tY

I have an later GM hydra-matic so familiar with the situation. Finding mechanics that are knowledgeable on these trans is getting to be an issue. I'm not familiar with the P ultramatic, but would have similar evolution.