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Old 07-08-2008, 09:49 AM   #7 (permalink)
Master EcoModder
Join Date: Feb 2008
Location: West Coast, USA
Posts: 513

B2300 - '96 Mazda B2300 SE

Focus - '05 Ford Focus ST
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Oil change interval depends upon vehicle driving cycles. If you're going to use the 7500 mile interval, you'll not be doing many short trips. The longer trips, say 20 miles, allow the oil to evaporate water condensed in the oil while cooling. High water content is not your friend.

Use regular dino oil and change it at nearly the longest interval that is recommended. Changing a little early isn't a bad idea, but every 3000 miles just costs you more time and money, and creates more waste oil for the shop to heat thier place with in the winter.

****If you really want to know how long you should use your oil, contact an oil analysis lab. It is often done by mail, so it's convenient too. The analysis is often less than $20 and could safely allow you to double your mileage between changes, paying for itsself in less than a year! Plus you aren't doing this blind, you'll have lab results backing up your decision, not some peoples guesses on an internet forum.

Contrary to what others state, I continue to believe that dino oils are so good these days that synthetic only might have an advantage if you have an optimal driving cycle to keep water content way down, and have really excellent (and more expensive) filtration. If you do all that you can still get really long life out of cheaper dino oil. Synthetics are best used in very high performance engines where greater heat and stress demand more consistency and reliability from an oil that what dinos can provide.

Big rigs use dino oil while getting many hundreds of thousands of miles from the engine. They also use filtration down to 1/10 micron. Typical good quality automotive filters go down to 10 micron, cheapies are 20+.

Our generators at work use 100 gallons of oil per change. We have 5 of them. Change them about every 3 years depending on the oil analysis results.
Good design is simple. Getting there isn't.
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