Hoping not to start another oil thread that goes south. I need some oil for the rear end of my coupe, its an original model A. It has a later gearbox so I only need it for the Diff. I do not have access to 600W here in Japan. Having read lots of posts and now having 'paralysis through over analysis' Am I good to use 85W140? https://www.monotaro.com/p/5565/8645 https://www.amazon.co.jp/-/en/TAKUMI.../dp/B075TTM9XG Thanks.
I personally use a half quart of Lucas Oil stabilizer and top it off with 85-1 40 oil and haven't had any problems even in the stock a gearbox. This is in my mildly hopped-up Model A Cabriolet with stock running gear
Modern oils will work well. You can get the "clinging" effect by mixing 85-140 oil with STP or similar (Lucas oil stabilizer?). If using modern oil it is a good idea to leave the oil level 3/4" below the bottom of the fill plug hole to help prevent seal leakage problems. Some of the 600 weight oil sold by the Model A parts vendors appears to my calibrated eye balls to be nothing but 140 wt. Snyders Antique Auto Parts is probably the best bet for the good stuff.
600W and 85W-140 are two oils rated on different scales. One is ISO steam cylinder rating, and the other is SAE lubricant. The Viscosity Index, ASTM D 2270 of 600W is: 95. The Viscosity Index, ASTM D 2270 of 85w-140 is: 97. The use of 600W as a gear lubricant in an vehicle is obsolete. My oldest service manuals go back to 1937. By then, there is no mention of 600W in any context. Ford had switched over to SAE gear oils.
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