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93 300E 2.8, 79 450 SLC
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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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1985 W123 200, 1980 C107 450 SLC, 1979 C107 450 SLC
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My '87 VW MkII used to have noise valve lifters, until a friend suggested I use a motor oil for diesel engines. Sure enough that cured the noisy lifters. I have also been advised against using the thinner synthetic oils in older cars because of the larger clearances in these older engines as compared to newer engines. The argument being that the thinner oils drains out very quickly resulting in increased wear on start up. I'm not sure I agree this this last statement as a thinner oil would much easier be pumped throughout the engine on startup, but I do agree that, because of the bigger tolerances in the older engines, they will not benefit nearly as much from the thinner synthetic oil as a modern engine would.

Any thoughts on this? Am I just talking through my ass?
 

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'80 450SLC Afro RHD Ikonengold
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There are many controversial tuneups and the least favourite in my book is the oil viscosity change.
If you go with thinner oil you must have oil pump for such oil too and incompatability may result in low oil pressure... the quick and the dead
Thicker oil will achieve higher oil pressure - but later, and most of the engine wear is at start up. Slow but sure death.

Original link has a good point with regards to combustible detergents in the diesel oils in relation to rings blow-by of oil into cylindre. I guess it may not be such an issue as M116/M117 engine is a low compression engine anyway.
I would also think that diesel engine oil does not have proper protection for higher rpms in a petrol engine.
I wonder what type of oil use those petrol truck I've seen (only) in Africa?
 

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1987 560SL AMG, 1977 BMW 533i Turbo
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I use valvoline VR1 Racing oil 20w-50 in all my cars because it has one of the highest zinc content of any shelf oil available
 

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450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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Thanks for the information! I'm not too worried about my catalytic converter. Finally something redeeming for this car not having a catalytic converter.

What's up with ll of the talk about rebuilt motors? Are they saying non-rebuilt motors are less likely to the problem because they've likely had the Zinc-buildup over the years (and it's less likely to wear away quickly)? Or are they just using rebuilds to have a better controlled sample set?
 

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This was a big issue when I owned a 1967 Volvo 1800S with a 2 liter "redblock" engine. The issue pertains mostly to pushrod engines with flat-tappet cams/lifters. I don't think it is really something to worry about with these SOHC motors.

As for the rebuilt engine issue, it's because original engines that have lives for decades with sufficient zinc apparently become strong enough to be fine even without the zinc. When you try to rebuild one of these engines with new parts, though, it will need a normal dosage of zinc for at least the first couple of oil changes. After that it should be fine.

If you must have zinc, the Valvoline VR-1 is a good choice, though as a racing oil it lacks some detergents and other ingredients of normal street oils. Also, Castrol Syntec in 20w-50 has high zinc levels (it should say "formulated for classic cars" on the back of the bottle).

I believe diesel oils are fine in gasoline engines, but some may disagree. The Subaru WRX/STi community absolutely swears by Shell Rotella T-6, a 10w-40 full synthetic diesel oil. These guys run their engines hard; they should know. I have used this oil (not in an R107 though) and really like it.

As you know, the reason zinc content has been reduced in modern oil formulations is that it has been shown to shorten catalytic convert lifespans.
 

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87 560SL
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This is a hotly disputed subject with experts on both sides of the argument.

Automotive engineers point to oil company endurance tests that show older engines doing just fine, some rebuilders argue just the opposite.

The big potential weakspot is flat tappet lifters, primarily during break-in (which is where the rebuilders see problems) and very aggressive cams (where the hot rodders see problems).

Zinc based oils are still available, as are zinc additives to use during break in periods. Zinc itself is not a pollutant, but it does shorten the life of the exotic and expensive catalytics that government is mandating for newer cars. Zinc in older cars does no harm to the car or to the air.
 
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