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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
Lots of work on Brad's part ... pure enjoyment (and references) for you!
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For helping keep this great
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| | | | Joined: May 2001 Posts: 1,904 'Bolter | | 'Bolter Joined: May 2001 Posts: 1,904 | According to my '48 owner's manual, a single number like 90 (w/o the W) is a defined viscosity at 130 deg F. The W indicates a viscosity scale determined at 0 deg. The 80W-90 gives the extra cold info but it seems to me the 90 mineral oil has a W number that could be measured but it just isn't given.
I mean, 20W-20 used to really puzzle me.
I haven't bothered to Google the modern definitions and I'll just rely on my owner's manual. I use the 80W-90.
1948 3/4-Ton 5-Window Flatbed Chevrolet 34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
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