What is your criteria for "short trip"?

Ho Folks,

Since we've had a lot of talk about oil, aging, dilution, and acidity i thought i would post some data from a recent oil analysis report.

This sample is from my Audi S6 (V8) after 4400 miles and (get this) 15 months. A significant portion of this is highway mileage to Vermont/etc.

I was concerned that even with the low mileage, gas, water and other contaminants would accrue in the oil, and would not sufficiently burn off in commutes. Note that as we have discussed this, i have become more careful about short trips followed by storage. I really try to get each car good and hot once a week, and before any extended sit.

Apparently it works. You can see my last sample had just under 2% dilution. This sample is below the reporting threshold of 0.5%. Marc reported nearly 7.5%. My track car is always below the measurement threshold, by the way - yea, track use gets things hot.

The net out for me is that if one DOES pay attention to the short/long trip mix and timing, oil can last a long time. This oil still has good viscosity (>11 at boiling) and TBN (3.7) and could have gone another 6 months very safely.

Oil, for the record is 5w40 from a major manufacturer, but supplied from the lab ( i was a guinea pig). It is intended to meet ACEA A3/B4 and VW505 but of course was never tested being a one-off.

[i57.tinypic.com]

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Not sure about Mg. Titanium is used by some formulators as a barrier lubricant similar to what ZDDP used to/does do. For example, its one of the distinguishing components of true Edge vs Edge/SPT (which is really syntec).

So, under circumstances when hydrodynamic lubrication fails, it performs a barrier (sacrificial) function.

Apparently the process to make it usable in base stock is quite costly, so its not always used.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I'm curious as I now own a car that, because it is a hybrid, doesn't run the engine all the time. Yet the engine is well known for 300k+ miles in that application. Think long commute or taxi. Most of those reports are from very intensive use per unit of time cars through....like 100k per year! The oil change interval is not significantly different than the Boxster's though the viscosity is. Likewise the probable RPM.

insufficient time for the oil to universally heat up to > the boiling point of contaminants ( which range from ~ 170 deg to 212 deg) for long enough to boil them off.

The way i see it, motors go through 3 phases:

1. cold when they run rich, generate lots of washdown and H20 and therefore actively dilute the oil
2. > cold but < boiling where the contaminants remain, btu little added harm is being done, and
3. > boiling wheile the oil's condition is being improved

The depends on time, ambient temperature, and how hard the car is run.

My personal take is i need to see the water at stable temp (186) for some time before boiling is happening. I wish we had an oil temp and pressure gauge.

In my S6, which has one, oil lags water significantly, and never reaches 200 deg except on track. but fortunately, local oil temps are much higher.
(is that a good thing? i suppose its mixed)

Under most circumstances for me that means <15 minutes is bad.

Note that my dilution is very very low. Note also ( i hate to misquote Marc today, so let's hope i'm right) that Marc had one sample with 7.5%. We'll assume that was an outlier.

here's my real answer: i take my bike to the gym not only for the cardio benefit, btu to leave the car home for the 2+ mile ride. I try to cluster shopping - e.g.; on the way home.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com