Author Topic: Used Oil Analysis  (Read 1231 times)

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Offline figbat

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Re: Used Oil Analysis
Reply #10 on: September 23, 2021, 03:16:39 PM
*Originally Posted by patgm [+]
I recently had a used oil analysis done and wanted to share the data.  This sample was taken at 3,850 miles on the odometer, so about halfway between the first service and the second service.  The first service was performed at 600mi by the BMW dealership.

Highlights:
    All wear metals were elevated compared to average, this is unsurprising, as the engine is still wearing in.
    Fuel dilution of the oil was severe at 6%, this compromises the viscosity of the oil and can accelerate wear.

The fuel dilution is likely a result of riding daily for commuting purposes, which is less than 20 minutes at a time, enough to get the coolant  to operating temperature for only about 5 minutes, which may not be long enough to get the oil to operating temperature. It could also be related to the cold start issue, which was problematic when new, after the first service, and again after changing the oil this time. Unburnt fuel is dumped into the cold combustion chamber on each failed start, possibly allowing it to seep past the rings and into the crankcase. Perhaps fuel dilution lowering the viscosity of the oil makes cold starts easier as more fuel accumulates in the oil? This logic is a bit cyclic since the dilution may be alleviating the cold start issue, while also being caused by the cold start issue.

If anyone else gets a UOI done, I'd appreciate you sharing your results to compare against.



Mind if I have a go?  I have 29 years' experience of lubricant product development and technical support including time running an investigational laboratory.

Looking at those data, my takeaways are:

Wear metals (Al, Fe, Cr, Sn, Pb) - no issues there.
Contaminant elements (Sn, Ba, Na) - no big issues there although the Si is a little high - there is a small amount of Si in the oil as an antifoam but higher levels can suggest operating in a sandy or dirty environment and/or reduced air filter efficiency.  Do you live by the coast?
Additive elements (Mg, Ca, Zn, P, Mo, B) - I tried to find a data sheet for the fresh oil but failed; it's difficult to say what's going on without knowing the starting point.  It all looks pretty normal though.

Properties - here we have a few issues:
- the viscosity is way down; I'm not sure where they get their "Values should be" from but to be a 5W-40 it needs to be between 12.5 and 16.3 cSt.  Your value of 8.62 puts it in SAE xxW-20 territory!  :005:
- the fuel dilution of 6% is huge and probably explains the viscosity loss.  It also explains the dangerously low flash point.
- on the plus side the insolubles are nice and low and the TBN nice and high.

If you are short-tripping then this could explain the fuel dilution.  You need to get the oil hot to evaporate any fuel that gets into it.  The good news is that there doesn't seem to be any wear, which is a possible consequence of very low viscosity.  If your journeys are longer then there is a fuel leak into the oil somewhere assuming the oil is what you say it is and isn't a low viscosity oil from another application (again a fresh oil sample would expose this).

Online rcb78

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Re: Used Oil Analysis
Reply #11 on: September 23, 2021, 03:21:53 PM
Don't know about the fuel and coolant but my iron didn't come down until sometime after 10k km, which was also when it stopped using oil.  My guess is the rings finally seated fully.
They say that "per mile" my current numbers are ok, hunting that they don't agree with a 10k km (6k mi) interval.  My plan is to try 4k miles (6500km) for my next oil change and send that sample in.  If the per mile improves then I'll stick to 4k mi intervals.  If the per mile is the same, then no reason.  The thought is that changing it before it shears too much will help.
I may also try a 10w-40 next time and compare.  A smaller spread should help reduce breakdown with time and it rarely gets below freezing here so a 10 base should be fine.

Online rcb78

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Re: Used Oil Analysis
Reply #12 on: September 23, 2021, 04:45:20 PM
Someone pointed out earlier that my linked report didn't redact my personal info so I pulled it awhile back and never got around to reposting.  Since this thread has come back to life here is mine, numbers are there for both the 6k and 12k mile services.

Oil Analysis

Offline patgm

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Re: Used Oil Analysis
Reply #13 on: September 25, 2021, 02:09:09 PM
*Originally Posted by figbat [+]
Si is a little high - there is a small amount of Si in the oil as an antifoam but higher levels can suggest operating in a sandy or dirty environment and/or reduced air filter efficiency.  Do you live by the coast?
Nailed it, very dry and dusty here in the San Francisco bay area, haven't had a drop of rain in months, so no big surprise that there's some Si getting into the motor. Is this something that would warrant slightly shorter oil c

*Originally Posted by figbat [+]
If you are short-tripping then this could explain the fuel dilution.  You need to get the oil hot to evaporate any fuel that gets into it.  The good news is that there doesn't seem to be any wear, which is a possible consequence of very low viscosity.
Right again: too many short trips. I do monitor my coolant temp closely, and thought I had it hot long enough to get the oil up to temp, but clearly not. Would be nice to have an oil temp readout to know how much longer it takes after the coolant is hot. It's a good excuse to take some longer rides more frequently though.

*Originally Posted by figbat [+]
assuming the oil is what you say it is and isn't a low viscosity oil from another application (again a fresh oil sample would expose this).
I can only trust that my BMW dealer filled with the correct viscosity.  I do find it interesting that some of the additive numbers are quite different from RCB's, since its the same oil, same dealer, same motor, same geographic area, the only difference should be that his is from a retail bottle, mine is from the dealer's bulk supply.

Thanks for your insight!

Offline figbat

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Re: Used Oil Analysis
Reply #14 on: September 25, 2021, 02:49:22 PM
Water temperature goes up quickly because there is a thermostat meaning that only the little bit of water in the engine gets heated to start with, then when it’s hot enough the ‘stat opens and the coolant in the radiator joins the circuit.  With the oil, the whole charge needs heating up so oil temperatures usually lag behind coolant temperatures by some margin.

Offline figbat

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Re: Used Oil Analysis
Reply #15 on: September 25, 2021, 02:52:23 PM
*Originally Posted by patgm [+]
Nailed it, very dry and dusty here in the San Francisco bay area, haven't had a drop of rain in months, so no big surprise that there's some Si getting into the motor. Is this something that would warrant slightly shorter oil c
It was the Si that made me think of sand/dust, and the Na made me wonder if you were coastal.  The levels aren’t concerning so I wouldn’t use this as an oil change trigger, the bigger concern is the viscosity.

Online rcb78

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Re: Used Oil Analysis
Reply #16 on: September 25, 2021, 04:48:38 PM
*Originally Posted by patgm [+]
I can only trust that my BMW dealer filled with the correct viscosity.  I do find it interesting that some of the additive numbers are quite different from RCB's, since its the same oil, same dealer, same motor, same geographic area, the only difference should be that his is from a retail bottle, mine is from the dealer's bulk supply.

Thanks for your insight!

Well we can test that next time i check since my current fill is from the dealer.  They replaced my oil pan due to weeping at the seam and i asked to pay for the extra qt and filter to get a full change at the same time since it was at the 12k mark.