Three thousand miles - fact or friction?

There's been a lot of confusion over the old stand-by three thousand mile oil and filter change interval lately.  Lemme 'splain the facts, keeping in mind that any rule like this is a vast generalization, since no two snowflakes are exactly alike (and neither are any two driver/car pairs).

The three thousand mile (from now on I'm gonna type "3,000 mile" because it's easier) rule was a very sound one years ago for almost all drivers.  When I started working on cars, it was cause for comment if somebody had over 100,000 miles on their car.  Today, almost any decent car can easily go three times that with a reasonable amount of care.  There are many reasons for this, one of the biggest being the demise of the carburetor and the distributor, and the advent of computerized fuel and spark delivery.  If you want to know how that revolutionary change allowed engines to run so much longer, ask me, and maybe I'll get into that.  But I hate typing.

Anyway, because engines wore so much faster years ago, the seal (no, not the cute mammal in the circus) between the piston rings and the cylinder walls was much looser, much quicker than in modern cars.  This meant that the oil was much more quickly contaminated with raw gasoline and combustion byproducts, as well as the particulate contamination that was a result of the faster wear in the first place.  Guess how you get rid of that contamination - right, you change the oil and filter!  So, in the old days, 3,000 miles was a good guide for most people.

Today, 3,000 miles is still a great guide - for some people, not nearly as great a percentage of drivers as it was in the past.  Many manufacturers still recommend it, but lots of people can safely extend their changes to 5,000 miles or more.  I think that about the only factor in oil change intervals that has changed with modern cars to decrease the oil change interval is the fact that lots of the new oil filters are tiny, and so cannot hold a great deal of trapped dirt and particulate contamination.  Coolant temperatures in modern cars also tend to run hotter, but I'm not sure that this is true of oil temps, at least to the point of affecting oil life.

The tack we've taken at DOC Auto is to allow our clients to decide what oil change interval they'd like to use; if you want some input from us, we'd be happy to help.  We can tell you what your car's maker suggests, and brutally interrogate you on your driving habits.

Hope this helps!

Dave
DOC Auto