> I don't see much similarity between '80's Chevrolets and late model BMWs as far as engine technology goes.

When it cones to wear and things oil impacts, I see a lot. Has BMW gone away from plain bearings? Are tolerances and clearances bigger or smaller in newer engines? Are newer engines more or less susceptible to oil viscosity changes?

Newer engines are more demanding of oil than older engines. The justification for longer oil change intervals has much more to do with engine oil changes than with engine design changes.

While I must admit I am not an "engine man," I also have a Mechanical Engineering degree and a bit of a mechanic background.

So you may be quite correct, but since I do my own oil changes, I personally prefer to err of the conservative side and not go for the extended oil change intervals. As a former Product Planner for Ford, I do remember being in a couple of meetings between marketing and the engineering people arguing about service intervals, with the Marketing people pushing hard to extend the intervals, to get a sales advantage, and the engineers arguing against extending them. It was more like an adversarial negotiation than discussion of facts.

I imagine even BMW internally has similar "meetings."

From the little bit I have read, a diesel engine relies to a larger degree on the fuel for lubrication of the fuel pump and (not sure on this part) the fuel delivery system. In a gasoline engine, the fuel provides little or no lubrication function. As for the rest, I am all ears to those that know what the heck they are talking about:popcorn:

On a seperate note, I am amazed by all the folks here that own fancy, expensive cars (a friend of mine just saw my car and asked if I will still be speaking with him) and do their own oil changes.... Whats up with that:thumbup:

> am i incorrect in my opinion that a diesel motor relies on oil performance more than a gas version does?

My understanding is that diesels are more demanding than gasoline engines, primarily due to soot contamination of the oil. The newer diesels may not have as much of a soot issue, but I suspect it is still one of the main limiting factors for oil in diesels.

Effect of diesel soot contaminated oil on engine wear

Dodge Cummins Oil Change - Diesel World Magazine

it is my understanding that fuel delivery in a diesel motor is provided by oil pressure. low oil pressure equals poor fuel pressure. poor fuel pressure in turn leans out the motor causing kah-blooey. :)

not terribly scientific but still.....

Might be a bit cleaner due to engine management but the big "clean up" is way after the gases have left the engine....The soot in our engines is scrubbed just before it hits the atmosphere. So the contamination I would think is still very much the same issue.

change the oil every 5k to 7.5k miles and keep the water out of your fuel. ahhh, the diesel bible. :)

It would be quite interesting to do an oil analysis on a BMW diesel and see the soot level at the recommended change interval.

I sent a litre off for testing after my first service, I'll paste up a photo of the result sheet and a comparative one from my nissan patrol

> do their own oil changes.... Whats up with that


Some of us like working on our vehicles. If you have to ask, you wouldn't understand.

OTOH, maybe Jay Leno could explain it to you...

Its not that I completely don't understand, I do my own oil and filter on my motorcycle, and used to do some pretty high-end stereo and alarm installs on my cars. But car oil seems like a real headache. I can barely keep the floor clean doing my bike. If I did the 35d they would have to call a Haz Mat squad to protect the local water supply lol.

Do you have a pit or something or do you crawl underneath? Maybe there is some trick to it that makes it easier - cleaner than it seems? At 150 a pop I could be talked into it, me thinks.