Rotella T4 10w30 in 1976 Mercedes 300D?

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Oddball car, W115 body with the N/A 5 cyl diesel that became known from the 77+ cars. It has under 140,000 miles and was well maintained. Lots of bickering on the benz forums about proper oil weight, not many running 30wt. I ran Edge 0w40 in it previously for about 2 years and a few thousand miles. It's a great sping/fall call to drive. I wanted to switch to T4 because I have gallons of it sitting here next to 15w40 Delvac in my stash. I'd rather not use the thicker oil and rob any extra of the cars minimal 88 horsepower.

I also don't feel like this engine, with the aggressive gearing and low power, is really working hard enough to warrant a serious diesel oil. But, I'm not a diesel guy or a Benz guy so what do I know. I planned to run a UOA after 3k on T4, if I use it.
 
Use the T4 and Delvac..

Your engine produces alot of soot/mile and you are best served with a dedicated diesel oil to keep that soot in suspension.

I would do frequent oil changes due to the high soot and possible fuel contamination of a less efficient engine.
 
The '82 300D (Turbo) I had actually had stuck rings due to being used with non-diesel oil, synthetic HDEO & long drives freed them up (M1 TDT/D1 5W40 CI-4)-I'm sure the T4 10W30 won't hurt anything, as long as it can keep decent hot oil pressure & doesn't leak out everywhere.
 
I ran straight 30 weight in my w123 240D OM617. Had the same hot low idle pressure as 15w40. (1.5 Bar)

Your car came with a recommendation to use 20w50 passenger car oil, IIRC. Anything's better than that, but something thicker that what I'm running in my prius might be most appropriate.
 
Originally Posted by eljefino
I ran straight 30 weight in my w123 240D OM617. Had the same hot low idle pressure as 15w40. (1.5 Bar)

Your car came with a recommendation to use 20w50 passenger car oil, IIRC. Anything's better than that, but something thicker that what I'm running in my prius might be most appropriate.
Actually, that's what gunked up my 300D, Castrol GTX 20W50 (at least that's what the PO had in the trunk). There's a chart in your owner's manual with recommended oil weights, personally I would save the 10W30 for winter and use 15W40 or straight 30 in summer, nothing is going to make an N/A diesel 123 a speed demon.
 
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This is the "updated" (relative to the 198x owners manuals we have in w123 cars) temperature-viscosity chart. There is an older one as well, but it's not as importsnt, IMO, as this one considers the newer (at the time) qualified grades of oil with ccmc G5 (IIRC similar to ACAE A3/B3 now).

https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=3045261

Personally I'd probably only run 10w-30 up to the straight 30wt ambient temperature, not the ccmc g5 number.
 
Ah, thank you for that. I couldn't find a chart. I did end up putting the 10w30 in the car. It sees 1000 miles a year or so, mostly in Spring/Fall. Not really a car I'm interested in driving when it's hot or cold out.
 
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