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My Automotive FAQ - What's your oil change interval?

Notice.  I encourage readers to determine a change interval that's appropriate for your specific driving conditions.

One issue I continually hear debated from time to time is the topic of oil change intervals.   With so much discussion centered around a recommendation to change your oil "every 3000 miles", I'm adding my comments into the discussion. 

Who are you listening to?  Making sense on this issues is rather confusing if you don't understand the dynamics of the industry and, more importantly, the players and their motives.  First, you have the auto manufactures who want to make their cars cost competitive, including tenance costs, in the eyes of the car rental companies.   Understand that car rental companies are (a) huge buyers of cars, and (b) carefully analyze the cost impact to their operation based upon "manufacture recommendations" for things like oil changes.  To the rental car companies, there's a significant cost every time they have to bring a vehicle in for service, even an oil change, not only for the parts and labor but the lost opportunity cost by have a car out of commission.  

Would you like some fries with that oil?  This is why the manufacture's recommended tenance schedule for nearly all cars contains both (a) 3000 mile, and (b) 7500 miles, schedules.  Then, you have the oil companies, who sell oil.  Now what do you think they are going to recommend, a long or short change interval?  Is it just a mere coincidence that a short oil change interval puts more money in their pockets?  Certainly, a shorter interval is better than an excessively long interval, and it's always safer to err on the side of caution, but not everyone needs a 3000 mile oil change interval.  

You mean I'm supposed to change the oil?   Thirdly, understand why oil is change in the first place.  I'm a computer consultant and work with a major oil company in Houston, and I have it on good authority by a few of their engineers that conventional oil breaks-down (short of excessive high temperatures) at the equivalent of 12,000 miles, on average.  This is to say that by breaking-down, oil starts losing its capability to lubricate as well as it should.   But do you know anyone who advocates a 12,000 mile oil change interval?  Not hardly, but why?  Because long before the oil breaks-down, it becomes contaminated with impurities from the combustion process.  Yeah, it's that whole blow-by past the rings thing.  Impurities get into the oil, causing not only the discoloration from translucent brown to opaque brown to black, but also a loss of lubricating capabilities.  

Would you like fries with that?   Additionally, every time your engine cools-down from operational to room temperature, a small amount of condensation appears inside the engine block.  This water further contaminates the oil.  Thankfully, for those who do not live within a few miles of work, studies have shown that 20 minutes of operation at operating temperature (195+) will effectively "dry-up" this condensation and also burn-off a good number of the impurities from the oil.  This is why it has become common knowledge that stop and go city driving with brief trips of 10 minutes or less, is harder on an engine (the entire car for that matter) than highway miles.  

It's hard to beat proven results.  When I pulled the head off my '90 Celica GT-S at 140K miles, there was absolutely no "ring groove" in the top of the cylinder.  In fact, I could see the factory cylinder hone cross-hatch in all 4 cylinders.   I bought the car new and always fed the engine a steady diet of 5w-30 Mobil 1 since hitting 1000 miles on the odometer.  And, get this, I used a 6000 to 8000 mile oil change interval, which is about every 3 months as much as I drive.

The So-What? of it all.    IMHO, the whole "you must change your engine oil every 3000 miles or it will die" concept/idea/theory is hogwash.  Presently, I use a 5000 mile interval on my daily driver (currently a '03 Tundra),  And, I employ a 1000 mile interval (which is about 6 months) on my All-Trac.

As always, your oil change interval may vary.

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