I have been changing my oil about every 3,000 miles and believed that was better than every 5,000 miles.
However I came across a study that stated that the most wear occurred in the first 3,000 miles the oil was used and decreased thereafter. The study was done using Mobil 1 and the test went on for 18,000 miles just topping up the oil and changing the filter.

The conclusion was:
Based on the results we've got here, we'd recommend 8,000 miles between oil changes on an engine that uses no oil at all, perhaps 10,000 miles on an engine that uses some oil, and 15,000 miles or beyond with a filter change every 5,000 miles. This, of course, isn't any kind of guarantee, and you must evaluate for yourself what your engine requires. One thing we're pretty sure about though: 3,000-mile intervals is a huge waste of resources.
The full paper can be found at:
http://neptune.spacebears.com/cars/stories/mobil1.html

Edit, I have an extended warranty that gives me two oil and filter changes a year at no charge, thats why I do it.

Edit, AMSOIL has similar claims (25,000 miles or one year) on its site;
http://www.amsoil.com/index.aspx
This site also lists filters, wipers, plugs etc. and access to Mothers car care products.

 

One thing to consider is that our cars have 8.5 quarts in the engine, meaning you should be able to go further between oil changes than cars using half the oil. And also these tests are usually done on cars with 5 quarts or less and are normally aspirated, so the extra quarts make a huge difference. Normally aspirated cars should go further on oil than forced induction ones. Just play it safe and change it every 7000 like the manual says...No need to change every 3000 unless you are using non-syntheticss which would be a no no with our cars. But then again, if you have the money to throw away, change it as often as you'd like. I always liked seeing clean oil on my dipstick!

 

I'm not sure about regular oil but isn't the trick with synthetic that it doesn't breakdown? Well at least under normal driving and not as quickly. I decided after a few 5k oil changes to just go with the 7k change recommended by Chrysler.

It would be interesting if a purely objective study could/would be published without prejustice. There are so many studies, papers, articles published on the internet and in magazines that contradict each other it is impossible to make a true choice.

I've put 350k miles on a Dakota V6 and 210k on a Ram sport with oil changes at 3k +/- miles. Neither every burned oil and have had no engine issues. Could I have gone to 5k with regular oil? Who knows?

 

Honestly, it just doesn't matter anymore which oil change interval is "right".

Each engine has different requirements, and even identical engines in identical cars still have different drivers, and different operating circumstances.

Driver A drives his car 100 miles all on the highway at 75 mph, every day, to and from work. His office and his house are just off the highway (turn right twice, you're there). He lives in an area that is neither hot not cold all year round. Can he go more than 3k miles on his oil changes? Hell yeah, but he insists on changing it every 1k miles, because he read on the internet that your car will blow up if its not done every 1k miles, and that's what his grandpa used to do with his 75 Ford Granada, with the inline 6 cylinder engine, and the 2 barrel carb. So yes, he changes his oil once a week. He's happy doing it.

Driver B drives his car 15 miles each way to and from work. The first 4 miles are slow speed driving on surface streets (30 mph and under, plus a school zone), then highway at 35 to 70 mph as traffic goes from crap to clear for 10 miles. The last mile is then surface streets at 35 mph. This person changes their oil between 7500 and 10k miles, and sends an oil sample to Blackstone every oil change to get an idea of how his car is doing, and has been doing so since he bought the car new, and now has 30k miles on the car. The oil samples come back perfect every time. Is he crazy for letting his oil change intervals lapse so long, or is he smart for testing his oil every time he changes the oil? Well, that person is me, so I have to live with it.

Driver C owns a Fancy sports car. Babies the car by keeping the engine rpms low all the time, hoping to get the car to last forever. Changes the oil every 10k miles like the car manufacturer says to. Has it changed at the dealership. Engine has a major internal engine failure, and dies at 20k miles. Dealer replaces engine under warrantee. Driver gets more concerned about the engine, and babies it even more, still having the dealership change the engine oil at the proper interval, still using the same Mobil 1 0W-40 oil, just like they are supposed to. Engine number 2 has the exact same failure as the first engine, this time at 15k miles. Owner goes insane, gets the engine replaced, and sells the car, never wanting another car from that company again. New owner doesn't baby the car, revving it up alot, changes the oil with the same Mobil 1 at the same 10k mile interval, and puts 65k miles on the car without any issues.

The third one is happening to owners of Porsche Boxsters, and is referred to as the IMS (InterMediary Shaft) failure. Basically, with the design of the flat-6 motor, instead of feeding the camshafts directly from the crankshaft in the engine, Porsche decided to create a shaft that goes between the Crankshaft and the Camshafts. One end of the IMS shaft turns the left bank (cylinders 1-3-5), and the other end of the IMS shaft turns the right bank (cylinders 2-4-6).

One end of the shaft just press fits into the engine block, and just turns against a machined surface. The other end has a bearing that is the same construction as the bearings in the pulleys on the front of the engine. It is also a sealed bearing, and contains the same exact grease in it that the pulley bearings do.

The problem is an owner that lugs the engine causes stress on the IMS shaft as the camshafts make their adjustments for better low rpm performance. The stresses on the IMS shaft wears out the bearing, causing its seal to be damaged, and the the lubricating grease for the bearing gets washed away by the engine oil. Then as the miles pile on, the amount of fuel in the oil increases past the 6k mile range from all the lugging, and because they are always running at low rpms, the oil never heats up enough to evaporate it, and the fuel further damages the IMS bearing.

Eventually the bearing fails completely, the IMS shaft seizes, and the pistons hit the valves, destroying the motor completely. A replacement motor from Porsche is between 11k and 15k dollars, not counting labor for install.

So oil change interval or even the type of oil you use isn't nearly as important as how you actually drive the car in relation to when you change the oil.

Just change it whenever you feel most comfortable.

BC.

 

Synthetic oil can go for 10k miles of regular driving. Especially when you have 8 quarts in the crankcase. But that's not the issue. All modern oils have many additives. They keep your engine clean, fight corrosion etc. All additives in a 4-5 quart system are burned out of the oil in 5k miles. So I'm thinking it's not the oil that will break down but the additives. Just another thing to think about.

 

If I was driving mine year-round, I'd go by the service oil recommendation given by the computer. The Germans are pretty smart about this stuff. But since I drive them summer only, I change the oil and filter before I store them for the winter. That means 10-12k of summer driving (when I just had the roadster), now that's split between two XFs. Most of the mileage is highway driving. I generally don't accelerate as hard as I can, but I do drive them briskly and occasionally at high speeds (>100 mph). I expect both to last a lot of years. BTW, I do the same with my Audi A6 2.7T and just passed 136k miles.

 

Maybe I'm weird, but I just wait until the car tells me its time for an oil change. I figure the car "knows" better than I do when it is really appropriate the change the oil.

 

I could go long and get into the complicted logic of wear and purpose and additives....et al.

Instead consider this when trying to calculate the value of oil changes.

Which cost more over the 150K to 200K miles expected life of the engine, the oil changes.....or the engine?

Change it at 6 to 7 K miles like the manual says.

And at least once a year. Whether it needs it or not.



roadster with a stick

 

I don't see much logic being applied at "spacebears.com".

AMSOIL's claims are flat out ridiculous. Are they saying that I shouldn't have to change my oil for 5 years?

We aren't driving 15 liter diesel semi trucks 50,000 miles a year. We are driving 3.2L Gasoline engines that rack up on average 13k a year. If that.

 

There are a few oil analysis labs that will tell you how well your oil service interval is doing. You send in a sample of your oil and they will tell you your wear metal content, what your oil's additive package strength is (i.e. how much additive life is left), ph, fuel content, etc. From that you can make an educated guess as whether you can go longer bvetween changes or if you've gone long enough.

 

Heck, the manual that comes with the car recommends that the oil & filter are changed every 7K. If the book says 7K why all the discussion?
Book say 7K, 7K it is!
If anyone wants to spend the extra bucks & change the oil more frequently, so be it. It's just a waste of oil, IMHO!
I've always thought that the 3K oil change interval has been over-marketed by the oil companies anyway. My Cougar manual says to change the oil every 5K, filter every other oil change.
Unless I'm driving the car through the desert every day or driving it in less than stellar conditions frequently I'll stick to what the manual says !

 

Ditto.....

 

I have 92K miles now. Changed my oil every 3k through 70K ( dealer paid ) since then I change my oil between 7~11K. last time was 11K. once I got the oil out, I looked at it (compared to the new oil, both Mobil 1) and decided there is very little visual difference. This motor should last another 100K no problem. Still running on original plugs and getting 26 MPG on 75 mile commute. So far so good

 

My car sit a lot, as I work from home, so I maybe crank it up twice a week at best. Is it ok to let it sit that way? Does the oil loose its viscosity, sitting? Should I at least crank it up if I am not using it?

Deb

 

If all you are doing is starting the car and letting it sit in your driveway, I would say you are doing more harm then good, for a number of reasons. When oil sits in a car, condensation builds up, which is completely normal. If you just let the car idle for 10 minutes, that may not be enough time to allow the water to boil off, which just isn't a very good thing. In addition, the whole act of idling your car for a prolonged time isn't very good for the engine.

So if it was me, I'd only start the car when I know I'd be able to drive it long enough to warm up the oil adequately. So IMO, it would be better to only drive once every 3 weeks than to let it idle in your driveway weekly. Now if you live in a very dry climate, the condensation in the oil may not be a huge issue, but idling for a prolonged amount of time, still is a concern.

Cars are meant to be driven.