Thoughts on oil change intervals and other fluid matters

How often should you change the oil in your car?  Should I follow the factory schedule?  Sometimes people ask why I recommend deviating from the factory service schedules for fluids in late model cars.  I hope my thoughts on this matter will help you make a good decision for your own vehicle. 

BMW and Mercedes introduced extended service intervals ten years ago.  Oil change intervals of 15,000 miles and even more were supposedly made possible by improvements in engine design and new synthetic oil technology.

When people adhered to that schedule, the results were mixed.  People who drove on the highway, and piled miles on quickly, often had good results.  By “good” I mean they did not suffer any lubrication related failures, and they got the economy of long oil changes.

People who drove mostly around town often had very different experiences.  Those cars often ended up going a year and a half between services, and when we pulled the oil filters, they were often nasty.  A number of those people had lube related problems – lifter noise, and worse.

That tells me the long intervals work for some people, but not everyone.  What’s the sensible solution?  Change your oil a bit more often, with the very best available materials, and whichever kind of driver you are, you should be safe.

With newer BMW, Mercedes, and Land Rover vehicles where a 15k oil change interval is recommended, I suggest reducing that interval to 10,000 miles or annually, whichever comes first.  If you do that on a 2011 Land Rover, Mercedes, or BMW, you will have an engine that’s just like new at 100k miles.

It is imperative to use the proper grade of synthetic oil with the correct extended drain additive packages.  Always make sure the oil you use meets the specific requirements of your car.  For example, some Mercedes, use an oil that meets MB specification 229.51 while others use a different spec.  A wrong choice could cost an engine.

The benefit of more frequent oil changes is extended engine life and the avoidance of sludge damage in the motor.  Since the cost of any such damage will run in the thousands of dollars, that benefit is substantial.  Offsetting that is the cost of the extra oil changes.  Over 100,000 miles, the extra cost of 10k oil changes versus 15k changes might add up to $700.  To me, that is a smart bet - $700 over 100k miles to avoid a multi thousand dollar engine repair.

If you have an older car where the factory calls for 5,000 or 7,500 mile oil changes I suggest you stick to that but use a good synthetic.  The synthetics have better detergents and they will keep your engine cleaner.  At the same time, the synthetic formulations last far longer than 7,500 miles, so oil failure should never be an issue.

The only cars I suggest get more frequent services are antiques with limited filtration and/or sludge in the engines.

In any case, I suggest doing oil annually if the mileage targets are not reached.

More extended drain fluids are found in the transmission, differentials, and power steering/hydraulics.  While synthetic oil technology has produced lubricants that should last ten years or more, that does not mean I feel comfortable leaving them in a car that long.

Few manual gearboxes, power steering systems, and differentials have filters.  That means any contaminants that get into the oil keep making their way through the system.  If dirt gets in, or pieces of metal invade the oil, disaster is ensured with those long change intervals. 

Another big risk is water intrusion.  Differentials in particular are susceptible to water intrusion.  I’ve seen several Mercedes 4Matic transfer cases that were ruined by watery lubricant as well.

For those reasons I suggest checking these fluids every 3 years-30,000 miles or wherever there is a visual suggestion of a problem. 

Automatic transmissions are a different matter, because they have filters.  However, they also put different stresses on their fluid, and having seen what gets drained out at 120,000 miles, I feel most ATF fluids should be done by 60k miles.  The idea of “lifetime fill” simply means a $5,000 repair if it blows up on your watch.  I’d rather up my odds and change the fluid every now and then.  Note that most high-end cars use special fluids and there are few if any generic substitutes. 

  

What about brake fluid?  The reason for changing brake fluid is that it absorbs moisture, which rusts brake components from the inside.  For many years, European carmakers suggested semi-annual fluid changes, and domestic carmakers didn’t suggest any brake fluid service at all.  The result was frozen calipers on domestics and very little trouble on imports with fluid service.

There have not been any changes in brake fluid technology and brake components are still made from similar materials as 20 years ago.  Therefore, I feel safe suggesting we adhere to the traditional once-every-two-years fluid flush cycle.  The exception to that is cars that get run on the track, where the fluid gets hot, because the heat cycling can accelerate moisture absorption.  For cars that run on the track I recommend annual flushes.

I think the fluid recommendations above represent a sensible balance that favors extending the life of the vehicle’s mechanical systems at minimal added maintenance cost.  They are based on my study of the cars and lubricants, and my 20-some years of experience as a service manager here at J E Robison Service in Springfield.  However, the final decision is up to you as the motorist.