jchapura

I think it's a common understanding that we should change our oil more frequently on the M97s to try to minimize a couple of expensive repair issues.

My question is this - is there evidence (used oil analysis or otherwise) to use a time-based (6 months? 12 months?) oil/filter change frequency when the M97-engined car is driven for longer periods (at least 40 minutes per engine start) but the 6-month accumulated miles is about 2000-3000, and the specific oil being used is JGR Driven DT40? Also, assume the M97 has an LNE low temperature thermostat.

rtl5009

In my experience, during cooler weather with a 3rd radiator and LTT installed, you are hard pressed to get the oil over 212 even with an extended drive. I have to drive the car hard to get it over 212 in the late fall/winter/early spring. Hence, 6mo is the number.

jchapura

I do not have the third radiator. Since you quote 212, I'll assume you are worried about water contamination.

What UOA value translates to (the products of) water contamination? Have long-drive long-interval UOA real results supported the conjecture?

rtl5009

The car generates a tremendous amount of water in cold start.

Sporty

Water in the oil, after sitting say for a week, after a good one hour run the prior week? - please elaborate. I assumed that if you run it regularly say once a week to full operating temp for an hour or so you would be burning off any moisture in the oil and it would take some time to build back up.

jchapura

And for everyone, please offer a UOA that shows an elevated "% water" or other technical indicator and offer the mileage or time-based conditions that produced it.

roadie13

You can estimate for excessive water/sludge build up by looking inside the oil filler cap. If it is full of green sludge then you're not getting enough temperature into the oil.
This was the case when I got my car from the dealer, which had me worried, but after some good driving the sludge disappeared and since then it has been bone dry.

Petza914

Oil becomes less basic and more acidic as it's used more. Acid eats metal so let's say after 3k miles in 9 months the TBN and TAN are about equal. As that oil stays in there and other 3 tony months it becomes more acidic. Leaving that acidic oil in there longer should increase wear metals. This mileage and time I just pulled out of the air as an example.
That being said, I go 4k-5k miles and 12 months on mine. If I'm close to the mileage range at 12 month, I might end up going 14 months if it will result in an even mileage interval that's easier to keep up with.

rtl5009

Fuel + O2 → CO2 + H2O

jchapura

But...
Isn't almost all the water going out the exhaust? Can you estimate the amount of combustion water that gets blown by into the crankcase? And doesn't the AOS take out almost all the rest?
Regarding the thermodynamics of driving off the water in the crankcase, have any studies been done to determine the rate of water drive-off under specific conditions?

jchapura

Can anyone point to one or more used oil analyses (UOA) posted on Rennlist, Renntech, 6speedonline, Pelican that is reflective of the below-miles-long-period-but-long-drive-duration oil change interval (OCI)?

Tcc1999

Water in the oil. Finally, a new(ish?) obsession.

jchapura

I can appreciate the humor in obsession(s)...

I'm also thinking about dilution due to fuel (flashpoint, reduced lubricity, etc.), TAN, TBN effects, and others.
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Fullyield

Jake Raby, Charles Navarro and Tony Callas all three suggest oil change interval of six months or 5k miles for reasons discussed by Petza above. That is good enough for me.

jchapura

No disrespect to Pete or the other gentlemen but was hoping for the evidence (UOA) to support the theory that Pete offers. I tend to agree with the theory but I also suggested a more specific set of driving conditions that might influence the results and conclusion. I wanted to have more than my own data point to guide my selection of OCI. Science over other factors.