2008 BMW M3, BMW TwinPower Turbo 10W-60, 4812 mi

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Previous UOA here. Now at 100261 miles on the engine. A little more than halfway through this OCI, my car threw a code for a precat O2 sensor (one of two). The precat O2 sensors on this care are widebands. As I understand, O2 sensors typically fail gradually, so I'm assuming this one -- and thus the engine -- had been running sub-optimally for some time before now. I'm also assuming the other one wasn't far behind. Maybe that partly explains my historically high fuel dilution numbers. Hoping so. Replaced both about 2k miles before the drain and the car ran noticeably better. Also ran a bottle of Techron in the fuel tank about 1000 miles before the drain. Copying the numbers here because Polaris's reports are kind of annoying to read: Iron - 8 Chromium - 0 Nickel - 0 Aluminum - 2 Copper - 2 Lead - 0 Tin - 0 Cadmium - 0 Silver - 0 Vanadium - 0 Silicon - 13 Sodium - 3 Potassium - 2 Titanium - 0 Molybdenum - 49 Antimony - 1 Manganese - 0 Lithium - 0 Boron - 47 Magnesium - 30 Calcium - 2365 Barium - 0 Phosphorus - 735 Zinc - 920 Fuel Dilution - 1.8% (GC) Soot - <0.1% by vol. Water - <0.1% by vol. (FTIR) Viscosity @ 100º C - 17.7 cSt TBN - 4.19 Oxidation - 12 Nitration - 10 Particle Quantifier (PQ) Index - 12

2019-12-07 - 100261 mi total - 4812 mi OCI.jpg
 
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you say little about the cars health + miles + sometimes electronics can be fickle. DIY is cheap but guessing BMW parts are NOT!!
 

d00df00d

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Originally Posted by benjy
you say little about the cars health
Zero identifiable issues at this point. In the past 20k miles, I've had a failed thermostat, one failed precat O2 sensor, one failed header-to-cat-section exhaust gasket, and a couple of minor fluid leaks. Pretty sure those are the only "health" related issues I've had. Anything else you'd like to know?
Originally Posted by benjy
miles
Mentioned in the OP.
Originally Posted by benjy
DIY is cheap but guessing BMW parts are NOT!!
BMW original parts are not cheap, no. Though not all are as expensive as you might think -- e.g., OE dampers for my car are slightly cheaper than the ones for my old Mazda RX-8. Either way, there are aftermarket options that save a lot of money. I use those sometimes. I buy everything from FCPEuro.com, which has a lifetime warranty on literally everything, including consumables (brakes, fluids, filters, wipers, etc.). Really takes a lot of the sting out of parts costs.
 

d00df00d

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Originally Posted by john_pifer
Those are some of the lowest wear metals I can remember seeing in a UOA. What's your usage like?
Important preface: I'd love to take this report as a clean bill of health, but unfortunately oil analysis is a terrible way to estimate wear. If the PQ index goes crazy or the numbers deviate significantly from the trend I'm accumulating, that might be something worth thinking about -- but low numbers don't mean all is well. That's probably better documented for this engine than it is for most, because apparently some have been known to produce good-looking oil analysis results (sometimes several) right up until they spin a bearing. Either way, I'm happy to explain more, though I wouldn't say anything that hasn't already been said by people who are smarter and far more knowledgeable than I am. With that in mind... This car is daily-driven year-round. No more than half throttle or 3k RPM until coolant and oil are up to temp. Mostly urban/suburban highway and suburban roads, a fair bit of rush hour traffic, some short trips. No track use (yet). The hardest driving so far was at the Tail of the Dragon this past summer. Although I'm not afraid of the throttle pedal or the top half of the tach, this is not an easy car to drive like that on public roads even if you have a death wish, so it's almost never anywhere near its envelope. The most I can say is that I don't upshift as much as I could and definitely accelerate harder than the average driver. My driving yields an overall MPG average that isn't much better than the car's EPA city rating, if that tells you anything.
 
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