b.searcy

I thought this was pretty interesting, especially the results page that pointed out that "this means that compulsive oil changers are actually causing more engine wear than the people who let their engine's oil get some age on it." Guess I'll be moving my frequency out to 5,000 miles.<ul><li><a href="http://neptune.spacebears.com/cars/stories/oil-life.html">Synthetic Oil Study</a></li></ul>

Fair Cape-Cape Town

I change my oil every 24000 kms which is almost exactly 12 months driving. I replace the filter every 12000 kms. After 14 years my engine is still perfect and oil consumption minimal.
I top up during the year with 500ml of oil per 2000 km and about the same when I change the filter which means that I actually get more than a complete oil change within the 12 month cycle.
The oil still looks fairly good when I drain it.

The reason here is that I drive 75% of this distance at speeds above above 100kph.

My wifes Toyota does about 8 kms a day and the engine rarely gets above luke warm. It never needs topping up. I change the oil in this car every 5000 kms because it gets black and sludgy. The engine is also in perfect condition.

Driving conditions play a big part in the frequency of oil changes.

islingtonaudi

I go about 10k miles on Mobil 1changes, maybe 60% highway.

A6Gary

oil every 3.0K miles. There testing was done over 1 million miles with dino oils using New York city taxis and showed no difference in wear of critical engine parts for oil changes at the factory recommended intervals vs. the 3.0K interval. The article also tested various oil brands and found no significant differences. Syn oil was tested, but their tests could not conclude anything due to some other factors and the number of taxis used for that particular test. After reading the issue, I stopped using the 3.0K interval and went with the OEM oil change intervals (or near the recommended mileage) and have had no problems in any of my vehicles.

Good for the pocket book, good for our country, and good for the environment. Winners all around.

tpierce

they are running most of the day, so the oil is always up to temperature. Cold starts is wear the motor gets most of it's wear, due to the lack of oil pressure. Also, the heating and cooling of oil causes it to lose it properties. Oil the never reaches a temperature above 212F+ will have water build up. It will also get diluted with fuel, as the motor will be running rich because the motor never reaches temperature. That is why there are usually two different oil change procedures, depending on how the car is driven. I've seen the inside of motors of lots of Volvos and Audis that go with the 7500-10000 mile oil changes, it isn't pretty. I have never heard of a motor failing because the owner changed the oil too much. As a matter of a fact, i have never heard of a 1.8t owner having the illusive oil pressure problem when the oil was changed every 3-4,000 miles.

A6Gary

build-up. The CR article also noted that their tests did not address the potential for sludge build-up due to short, cold trips. However, the stop-and-go driving of taxis will cause very sever wear of interior engine parts due to the fatigue cycling and very hot temps of that driving style. And that was the reason for their tests to compare different brands of oils.

Quoting from the article: "For "normal" service, 7500-mile intervals (or the recommendation in your owner's manual) should be fine. Change the oil at least that often to protect your engine and manitain your warranty. Even for the severe service experienced by the taxis in our tests, a 6000-mile interval was adequate. But some severe service - frequent cold starts and short trips, dusty conditions, trailer towing - may require shorter interval." CR also stated that they don't recommend leaving any oil - dino or synthetic - in an engine for 12,000 miles. Agreed that you won't hurt an engine by doing more frequent oil changes, but you will be throwing money away and using up our natural resources needlessly.