Another oil thread

[Cr from Texas]

I thought all oils for diesel had an API rating that started with C. Since new, I have use Castrol GTX 20w50 in my 617. In 1983 that oil had a CD rating. Now it is SL and I was concerned it was not diesel rated. I contacted Castrol and got this reply:

"Thank you for contacting Castrol North America,

For a 1983 MB 300D Castrol’s lubrication guide recommends an oil meeting API SL and the following:

Above 86˚F (30˚C)…………………………. SAE 40
Above 32˚F (0˚C)…………………………. SAE 30, 20w-40, 20w-50
Above 23˚F (-5˚C)…………………………. SAE 15w-40, 15w-50
Above -4˚F (-20˚C) ………………………… SAE 10w-40, 10w-50
32˚F to 77˚F (0˚C to 25˚C) 1980-85 ………SAE 20w-30
23˚F to 68˚F (-5˚C to 20˚C) 1980-85 ……..SAE 20w-20
-4˚F to 50˚F (-20˚C to 10˚C) ...…………….SAE 10w-30
Below 14˚F (-10˚C) ………………………….SAE 5w-20, 5w-30

Castrol GTX does meet API SL rating and so is still applicable for use in your vehicle.

Castrol Consumer Relations"

Do you agree that API SL is suitable for diesels? I had planned to switch to Delvac or Rotella. Should I stay with what the car has always used? I've had no issues except it has started leaking around the filler cap and I have a lot of oil in the air filter housing. Tried three new filler caps including the plastic one. No improvement.

[Skippy]

I would be concerned about using an oil that isn't diesel rated in a diesel engine.

[Cr from Texas]

Originally Posted by Skippy

I would be concerned about using an oil that isn't diesel rated in a diesel engine.

I agree, but is API SL a diesel approved rating?

[compress ignite]

The "SL" denotes a Gasoline engine SAE specification.ONLY!

You're correct...SAE Diesel rated oils are ALL "C" classification.

Regular Old Rotella T and the 300D will be happy...
Synthetic Rotella T and the W123 will think it's died and gone to MB Heaven.

Castrol has it's head up it's Keister,Here's what they recommend online:

[Cr from Texas]

Originally Posted by compress ignite

The "SL" denotes a Gasoline engine SAE specification.ONLY!

You're correct...SAE Diesel rated oils are ALL "C" classification.

Regular Old Rotella T and the 300D will be happy...
Synthetic Rotella T and the W123 will think it's died and gone to MB Heaven.

Castrol has it's head up it's Keister,Here's what they recommend online:

That's what I thought. So not knowing when the oil I'm using dropped the C classification and how long I've been using the wrong stuff, what should I do? Just switch to a diesel oil or should I be doing some kind of an oil flush treatment? I've always changed the oil and filter every 3K.

[vstech]

damage is done.
just drain your oil, change the filter, and fill with some synthetic rotella or M1. the synthetic, will be more than enough to compensate for any leftover S class oil...

Drain it and get the right 15W40 or 5W40 oil in there.
Thats what happens when you contact a third party company for important information like that. If you wanted an accurate answer you should have contacted Mercedes' Classic Center.

[Cr from Texas]

I'll do the switch but I assume I may have excess soot. I guess over time, the right oil will take care of the excess. I had planned to increase my oil change interval to 5K but I'll continue with a few changes at 3K to speed up the flushing. Thought I might need a flush treatment of some kind (If such a thing exists and works).

The original recommendation for the oil came from MB in 1983 when I bought the car. What I didn't follow was the changes in formulations and recommendations until I started following this forum.

Thanks to all who responded!

[F18]

Charles.....if you have been doing delegent oil & filter changes at 3K all along the engine should be just fine. But I would switch to any of the "C" or even better...the "CJ4" newest rating which the Rotella and Delvac diesel oils are compliant as suggested.

[compress ignite]

If you've been Changing the oil every 3k,
Just change to your preferred Diesel rated oil.

...And don't worry,those Damn 617s will probably run on Singer Sewing Machine
Oil if you changed it often enough!