boofer

sorry this post is so long.

scenario:

- you drive 12 miles to work and it's NOT stop and go (so it isn't "severe" driving conditions).
- you use a high quality synthetic oil.
- you check your oil and make sure that it is at the proper level at all times.

if you drove your car based on those factors, would the oil's effectiveness drop to zero after x-number of miles? my guess is yes, but at what # of miles does that occur? certainly it occurs well past the maintenance minder (which hit 0% after about 5,500 miles for me).

from what i know, the two main things related to driving in "severe" conditions are:

(1) unburned gas slipping past the piston rings, contaminating the oil
(2) condensation in the crankcase that doesn't fully burn off due to many short trips in the car instead of driving for at least ~10 miles.

those two things can lead to sludge, which can block oil from getting where it needs to be and therefore lead to engine damage. however, if you drive mostly easy highway miles, the chances of (1) and (2) occurring in the first ~10,000 miles are pretty low, right?

i don't track my car; i DD it to and from work against traffic in the DC area and therefore am almost never in stop and go. i never race, and i probably only VTEC once a day, if that. that said, i'm very busy with work and travel this summer, and changing oil, whether i do it myself or take it somewhere, takes time.

other than peace of mind, why do people really change their oil every 3,000 miles if driving conditions aren't through the sahara desert? i know i'll probably get IBTL's and a bunch of other sarcasm, but is there any evidence anywhere of engine damage from lack of oil changes but without any sludging, so long as the oil level/pressure is kept up?

another reason why i posted is because BMW/Mini is stating that their oil change intervals are 15,000-20,000 miles. WOW. of course, they stated that at the same time that they started offering "free maintenance" through 50,000 miles. anyway, any input would be nice.

thanks!

gotswap

Best answer is to do an oil analysis at your next oil change. They can give the the wear properties and oil change interval.

Blackstone labs

slalom44

I agree with your logic. Long drives minimize fuel dilution and condensation. The heat from a long drive will also remove any diluted fuel and condensation, allowing your oil to last longer.

Condensation is a problem for many reasons. It pulls sulfur (product of combustion) from your oil and forms a dilute sulfuric acid which can cause corrosive wear and reduce your TBN, hence your oil life.

I agree with gotswap - an oil analysis will tell you how far you can push your oil. I do a lot of long distance driving and I have really long OCIs (last one was over 24k miles). My UOAs tell me that my oil is still in good shape and doing its job. Since my setup is significantly different than yours and my long trips are much longer than your daily trips, you really need to do your own UOA.

Personally, I don't think a 12 mile trip is "long". It's not short, but it probably isn't long enough to make up for lots of short trips. You still may have a little fuel dilution, and it would show up on a Used Oil Analysis. If you get a UOA, make sure they test for TBN (total base number). That tells you how much life is left in your oil.

JDM06S

JackS

Lube qualities of oil would never dissapear. Other factors as already mentioned do accumulate. Dirt and water may eventually become the main ingredients to subvert any lube properties the oil still has or had when new. Additives and lube enhancers that oil mfgs use probably would dissapate or possibly change properties given enough time.

NFRs2000NYC

The truth is, most modern synthetics can run to damn near 100,000 miles. It will be carrying a lot of dirt and carbon, but it will still lubricate. Most modern oils don't even break down. You can safetly run synthetic oil for 15K without batting an eyelid.

INDYMAC

The most common UOA interpretation would include TBN as the deciding factor as to whether oil is spent. For this, Blackstone Labs is a good value at $32.50.
For a more thorough and useful UOA interpretation, TBN/TAN/Oxidation/Nitration/Water/Soot would all be considered. For this, Dyson Analysis is the best value at $60.

Nate4635

Yea....oil will last a lot longer than people believe.


Its not as if the manufacturer suggests 10k changes, and then at 10.1k the oil disinegrates and your engine blows up.

There are so many things that can affect the magic # of miles you can drive on an oil change.

dezignpro04