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| | | Forums66 Topics128,154 Posts1,056,850 Members48,456 | | Most Online14,466
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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| | | | Joined: May 2001 Posts: 1,907 'Bolter | | 'Bolter Joined: May 2001 Posts: 1,907 | The 15W-40 diesel oil lubricant is traditional oil from petroleum.
I've noticed that synthetic/traditional blend is 10W-40.
Pure synthetic is 5W-40.
I take that to mean synthetic is a much better lubricant at cold temperature and they can get away with a less viscous oil on cold startup.
I use 6 quarts 10W-30 Mobil One synthetic (NAPA 1072 bypass oil filter) in my 261 and now change it once a year although I could go much longer than that. It gives me a chance to crawl under my '48.
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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