SAE 30 vs 15W-40 - PeachParts Mercedes-Benz Forum

tobybul · #1 07-24-2007, 01:18 PM

Is straight 30w oil ok to use on the D's? what about 5w-30?

WINGAS · #2 07-24-2007, 01:31 PM

To me 5w-30 is too light for propr lubrication of the cam follwoers. Most modern engines recommending 5w30 use roller followers. A nbrand new engine, sure. high miles. No way.

Straight oils are what we use for new engine break in. Better lubricity and shear properties I;m told. Cheaper too, good for one hour oil.!

USE 15-40 fleet. Engineered for these engines.

patbob · #3 07-24-2007, 01:40 PM

Quote:

Originally Posted by tobybul

Is straight 30w oil ok to use on the D's? what about 5w-30?

The only owners manual I have convenient is for an '89 560SL (came with the FSM) says it'd be OK above 0F. Dunno if that applies or not.

However, it'll make starting a bit more difficult, and probably won't afford as much lubrication at the higher temps.

Why do you want to use straight weight oil anyway?

winmutt · #4 07-24-2007, 02:02 PM

Oil debate beaten to death. Do not use any oil that isnt rated for Diesel.

#5 07-24-2007, 04:43 PM

If you want to use a straight weight oil, use a diesel rated 40wt.

WD8CDH · #6 07-25-2007, 08:59 AM

I would stay away from straight weight oil even in the summer. Stick with a 15W-40 or even better a 5W-40 diesel rated synthetic.

Straight weight oils just put too much stress on the starting system and don't lubricate the engine as well during warm up.

F18 · #7 07-25-2007, 11:13 AM

If the oil is not diesel rated and carry all or one of the API ratings of CJ-4,CI-4 Plus, CH-4, CG-4 or CF-4 don't use it no matter what the weight is!

Diesel oils have a whole seperate package of additives/detergents in them that keep the carbon soot in suspension. Gasoline oils do not have some of thoughs additives or the high level of detergents. And as far as I know I have never seen a straight W30 that is diesel rated. Using Gasoline rated oil would allow the carbon slug to build up in the oil passages .....then you have an oil starved engine over time (spun bearings, fried turbo etc.).....not good!

WD8CDH · #8 07-25-2007, 11:52 AM

Shell Rotella is available in SAE 30 and SAE 40 but it is only CF-4 (which is still higher than the CD rating from 1985). But the Rotella multigrade oils are rated higher at CI-4 PLUS.

About the only "auto parts store" "consumer" oils that I have seen with a diesel rating are Mobil oils which often have a CF rating which is slightly higher than the diesel rating from the '80s but still lower than the current comercial products.

The only reason that I mention this is that if you want something thinner than a 15W-40 oil in the winter but don't want to go with a synthetic, you could use a Mobil 10W-40 conventional oil and still have a diesel rating and be in the viscosity range that a 617 motor needs.

Also if you need some oil to top off in an emergency in the middle of no-where, you can often find Mobil oils easier than the true commercial diesel oils.