Chuck540MZ

From the bimmer 5-series board.

Since I always change the oil every 4,500 miles or so, this post makes me feel better that I may not be wasting my money.<ul><li><a href="http://bimmer.roadfly.org/bmw/forums/e39/forum.php?postid=836037&amp;page=1">Oil changes &amp; analysis</a></li></ul>

Audi-Sav

and tire rotation at 5109miles

TXurS6

the way he comes to a conclusion based on the data is still suspect. He says that nitration was 100% higher. That means nothing to me if I don't know the initial value and what value is actually considered harmful. He also doesn't mention if he was using dino or synthetic. That would make a difference in how sludge and varnish build up as well as help explain the change in viscosity.

I am old school and I like frequent oil changes but I don't think he has settled anything based on his "analysis".

Chuck540MZ

I admit that some of his arguments have holes in them, but if the oil has deteriorated in any way before the recommended change interval, that's good enough for me to change it more often.

Chris JB

I use Mobil 1 and change every 8,000 miles. My driving is mostly highway, which I think makes a big difference. If I did mostly short trips around town, I'd change more frequently.

It would be interesting to do an analysis of oil over the same mileage, but different driving conditions.

Chris JB
00 2.7t

QCRAZY

...and should really state the brand to be accurate at all.

Not to stir things up too much but Porsche recommends changing the oil every 15k miles or 2 years.

Stoney

... compare values after 10,000 miles to those after 5000 miles ( what he did). Sure, the second change showed twice the nitration levels ("100% higher") than the first, but that is simply confirmation of expectations! Also, the weight was "within" a range whose lower end was the specified oil weight. So, a change of 0.1W would cause that... it tells us nothing.

The questions is, what values do you are required to have, and what values do you actually measure? At what mileage does actual exceed required?

Furthermore, he should exclude break-in, and test the same oil batch after its first 5000 miles then again at 10000. I know, that is not what he wanted to do for his car, but it would be a better test.

It also matters what oil he used, for example, Amsoil has a standard synthetic for high-performance cars and a "series 2000" designed for roughly twice the life.

TXurS6

and experience that synthetic produces little, if any, sludge or varnish. It of course degrades over time and it does get contaminated as well but I don't worry about varnish and sludge when using synthetic.

captainbilly

they used to claim that you could use it for 40,000 miles between changes (this may have been Amsoil's claim). They changed that to 10,000 (I think)but I decided to do some research and testing of my own. What I found in my research is that conventional multi-weight oils have a limited lifespan due to the viscosity enhancers breaking down. The multi-weight oil starts life as a light (less than 5 on a 5-30) single weight oil and then it has VEs added to give it the range. When the VEs break down you are left with 5 weight oil (or less). Other things happen to the oil such as acid build up and sluge but the main lubrication issue is the VEs. Synthetic oils don't typically use VEs, instead the oil itself is engineered to have the required multi-viscosity range. Because of this, most synthetics have viscosity lifespans that are so far beyond the oils ability to withstand contaminants as to be essentially unlimited. If you changed the filter every 5-10k miles and always got the oil nice and hot, so you didn't build up too much water, the oil probably could safely run past 40k miles. Synthetics are changed primarally because the additives package wears out and the oil gets filled with particles too small to filter out.

I did a test several times on a fixed up Datsun 510 that I had in the late 70s to try and see what would happen to the oil's viscosity as the oil got old. I found that main stream conventional oils would see significantly decreasing oil pressure (measured at idle and hot and indicating decreasing viscosity)at as little as 1,000 miles. Premium oils, like Castrol GTX, would start to loose pressure at 1,500 miles. Synthetic oils, including Mobil one and Amsoil, never lost any measurable oil pressure in as much time as I was willing to leave them in the car (a little over 10,000 miles, which was a lot in those days).

I have not had a car with an oil pressure gage, and or that ever showed anything other than steady oil pressure, since so I have not done these tests with newer conventional oils. My best guess is that if you want to run anything like 5,000+ miles between oil changes, and you want good lubrication during that entire period, you need to use a synthetic oil. Of course all this depends on many factors like; average oil temp, peak oil temp, oil temp at shut down, ambient humidity, level of blowby in the crankcase, etc., etc.

By the way, I am also an engineer (mechanical and electrical) and also have a degree in Physics, all from Columbia University. I really like these little efforts to try to quantify the basis for some of our opinions, even if they are incomplete or poorly controlled experiments. The results are, in my opinion, still more meaningful than, "I heard it from a really smart guy". The "chip wars" dyno tests, Vag-Com plots and oil analysis may not be perfect but they are much better than no data.

timcar

Very interesting. Thanks!