jackh@zehntel.UUCP (jack hagerty) (09/27/84)
>Also, there is a common misconception that the heavier the oil, the better >the oil protects. This isn't necessarily true. What is important is how >much temperature and pressure the lubricant can take without oxidizing ex- >cessively. This is where Synthetic lubricants excel. > > Dennis Dennis raises and interesting point and also a question I've had for a while now. In our area of California (Livermore) it gets quite warm in the summer and never that cold (rarely below 40 F) in the winter. I've always used 20w-50 in my Alfa thinking that I was getting the "protection" of a 50 weight when hot while not risking inadaquate lubrication when starting. I feel that this, plus frequent (3000 mi) oil changes, has kept the all original engine strong to 150,000 mi (and it's still going!) Imagine my surprise, then, when I found that the reccommended oil for our new Saab, even in our area, was 10w-30! I asked the service manager about this and he said that as long as the oil passes API service class SE-SF then it's all right. I know that the API service classes are tests of an oils actual ability to protect, not just its viscosity. In that case, the obvious question is: If a lighter weight oil can be made to pass the most severe test that API has, why do we need heavy weight oils at all? -- Jack Hagerty, Zehntel Inc. ...!ihnp4!zehntel!jackh