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I am running Mobil-1 so need to stay synthetic. But not sure what weight to use. Your expertise is sought and appreciated. I have about 75-80,000 miles on the engine. Thanks guys!!

(Guess it helps when I am clear about the model)

When I found Buster, the PO was using a synthetic.
I switched to Castrol 20/50 & neither car has complained.
I just change the oil every 3000 to 5000 miles.
My logic is; if the shavings are not drained,
they will be abrasive to the engine because they're still there.
To me, it's nothing but hype to be able to go 10,000 miles w/o changing oil.
Where do the shavings that were formed at 2,000 miles go?
Right back against the walls, creating more damage?
I don't mind if someone tries to change my mind with logic.
Good luck,,,Greg

Thanks Greg. Still want to stay with Mobil1. Just not sure if it should be 10-30 or 15-50. If others suggest a better synthetic, I'm all ears!

Oils have changed, mostly for the better, but M30s were built for 20-50 in a wide range of temps. The clearances were designed for thick oil. And they have proven extraordinarily long lived with said oil. 300K on the oily parts is almost routine, as long as the head hasn't cracked.

All of which is saying use the 15-50 if you insist on synthetic, not 10-30. 10-30 synthetic is a very thin oil, too thin for warm weather. Yes, synthetic is a better lubricant, flows better cold, but still has to fill relatively large spaces hot, and hold pressure.

awesome. Thanks Mike! I found several quarts of 15-50 in my garage and could not remember if that was for the Mercedes or the BMW and because the oil was older from sitting on my shelf for abt 9 yrs. I contacted mobil and they told me that the oil was no good anymore that it should not sit on my shelf for over a year or so because it breaks down. so I took about 14 gallons of various oils for my cars to the gas station for recycling today. how painful to see those dollar bills go into a 55 gallon drum like that. But I am glad to now be all the wiser. I never changed my oil before on an annual basis because I drive my e12 for way less than 3,000 miles a year. it matters not I now know. The oil must be changed annually. thanks again for your guidance. now I know that the 15-50 was what I was using in the BMW. and not the Mercedes 69 280 SL. that car is now running Rotella diesel oil even though it is a gasoline engine. Mercedes had a major announcement recently making this recommendation for all older Mercedes gasoline engine cars. huh!

As said above, modern engines runs at closer tolerances and will benefit from the smaller molecules of a synthetic. A lot of times, synthetics find ways out of the block past seals in our cars too because of it. Stick with Rotella, it also has the lubricants that are missing in present oils too, I run it in all my <90's cars.

Rotella diesel?

Shell Rotella T.

Two things. Is an 81 not modern enough for synthetic to be better? And i thought going from dino oil to synthetic and then back to dino was a very bad play as leaks would abound. No?

All of my M30s except the B7 Turbo get Valvoline VR-1 20w50.

I use mostly Mobil 1 15w-50 full synthetic. Occasionally, I'll put a quart of synthetic 10w-60 in from other manufacturers, but it's crazy expensive.

I'd always likely to see higher idle oil pressure in my warm climate, so I'm always using the higher viscosity formulas.

I use Walmart 20-50, any lighter oil and it smokes a little on decel. My idle pressure is about 25# and it runs 70# at 2500 rpm.

Walmart Brand?? Wow. Have you compared all the particulars?
I buy Castrol 20/50 from Walmart but, I haven't even thought about an off brand for my oil. Wow!
Castrol has been proven in racing, has Walmart? Who makes the oil? Is it cheaper?
Good luck,,,,Greg

I live in Texas where each day feels hotter than July...I use Royal Purple 20 /50 synthetic in my E12 (121,000 orig miles), and I still prefer to change the oil every 2500 miles or 12 months.
Redline MTL in the tranny.