Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site decwrl.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!whuxlm!harpo!decvax!decwrl!dec-rhea!dec-euclid!paulhus From: paulhus@euclid.DEC (Chris Paulhus 223-6871 MLO8-3/T13) Newsgroups: net.auto Subject: Transmission Lubricants Message-ID: <222@decwrl.UUCP> Date: Wed, 12-Dec-84 12:17:41 EST Article-I.D.: decwrl.222 Posted: Wed Dec 12 12:17:41 1984 Date-Received: Fri, 14-Dec-84 04:36:07 EST Sender: daemon@decwrl.UUCP Organization: DEC Engineering Network Lines: 45 A few comments on transmission lubricants: Originally (say 1950's and 1960's) manual transmissions used an EP rated oil, the EP standing for resistance to extreme pressure which occurs at the gear tooth contact point. In the late '70's, GM decided that stocking two fluids, an automatic transmission fluid (ATF) and an EP fluid was too much trouble for their dealers and redesigned their manual transmissions to allow ATF to function as a lube. ATF also has viscosity improvers that allow it to function better at low temperatures, similar to multi-grade motor oils. The EP rated oil was given a viscosity range rating higher than motor oils (despite having the same real viscosity range : a 90 EP oil has about the same viscosity as a 40 weight single grade motor oil!) so the two products wouldn't be confused (like us acoustics types are using decibels for sound pressure and Bels for sound power). So, a 10W-40 motor oil is similar to the 90 weight EP transmission lube of old, less the extreme pressure additives (but the new SE and SF motor oils do pretty good on this score), but with superior low temperature performance. Viscosity improvers (VIs) are long chained polymeric (sp?) molecules that coil up when cold and add nothing to the base stock's viscosity. As they warm up, they uncoil into thread-like strands. This effectively increases the viscosity of the mixture (base stock plus viscosity improvers). In highly stressed engines (high contact pressures, lots of shear stress at the lubricated surfaces - typical of higher rpm, smaller engines) there was a tendency for the long thread-like VIs to be sheared or cut, decreasing their effectiveness. After 20,000 miles your 10W-40 ended up with a bunch of chopped up VIs in a base stock of 10W oil, which didn't provide adequate protection at 180 deg. F (or more in VWs and such!). (Remember, the 40 weight is just the effect of the VIs on the base 10W stock.) This situation is better now than it was 20 years ago, but users of multi-grade motor oils - especially high rpm users - should be cautioned to obey the frequent drain intervals recommended. (The other reason for frequent drain is the breakdown of the other neat additives in the oil - anti-rust, anti-foam, anti-acid, etc. This is particularly important if the oil doesn't get up to temperature and volatize off the acids and other bad stuff.) Another 2 cents worth from: N. Chris Paulhus DEC-Maynard decwrl!euclid!paulhus (617) 493-6871