Question about Rotella T6 oil for my 84 300SD Mercedes

revdarkwing

revdarkwing

Joined
Apr 23, 2024
Messages
5
Today I am picking up a 1984 Mercedes 300SD and reviewing my motor oil choices. On Mercedes forums they are recommending Rotella T6 full synthetic. I have two questions about this. First, do you recommend anything in the same price range that would be better and
Second: I notice on the bottle it says 15 years or 500K miles guarantee. Can any of you tell me what that's about? They're not suggesting that you can go that long without changing it.. I'm pretty certain about that.
As far as frequency, I'm told that 5K is a good time to change the oil. Do ya'll agree with this and when I do change should I change the filter every time as well despite their mileage guarantees? In my gas cars I've gone with Mobil 1 and the top line Fram filter and changed both at about 6k.
Filter recommendations would be appreciated.
Thanks
 
T6 is an excellent oil for your older MB. The warranty details don't apply to your 1984 due to age. You'd have to read their Terms of Warranty to grasp what it means. I'm not up to date on them other than probably maximum mileage & age if you can qualify along with changing oil at specified time with their oil of course.
 
I wasn't planning on testing their warranty anyway.. seems crazy to drive a car that long without changing oil.
Would ya'll recommend full synthetic or the blended version. I've always gone full synthetic simply because I considered the blend a cheaper alternative for folks who didn't love their car as much as I did mine. Some told me that since synthetic oils weren't around when this car was build, it's best to use blended. I don't buy that theory but I also am ignorant about a lot of things when it comes to oil.
 
Welcome to BITOG, where we tend to overthink and overanalyze.

Try and keep it simple, you will live a happier life.

That said, T6 is a great oil for your OM617. Change it annually at minimum or at no more than 10K miles if you plan to rack them up (doubtful in a 40yr old Benz).
 
revdarkwing said:
Today I am picking up a 1984 Mercedes 300SD and reviewing my motor oil choices. On Mercedes forums they are recommending Rotella T6 full synthetic. I have two questions about this. First, do you recommend anything in the same price range that would be better and
Second: I notice on the bottle it says 15 years or 500K miles guarantee. Can any of you tell me what that's about? They're not suggesting that you can go that long without changing it.. I'm pretty certain about that.
As far as frequency, I'm told that 5K is a good time to change the oil. Do ya'll agree with this and when I do change should I change the filter every time as well despite their mileage guarantees? In my gas cars I've gone with Mobil 1 and the top line Fram filter and changed both at about 6k.
Filter recommendations would be appreciated.
Thanks
Click to expand...
As an ex MB owner I can tell you this:
Use only oil in the right weight range with the MB Approval number, follow the recommended OCI and do not use
those....... suitable for or meets....
also live by this maxim "Nothing is more expensive than to be cheap on a MB"
 
Pelican said:
As an ex MB owner I can tell you this:
Use only oil in the right weight range with the MB Approval number, follow the recommended OCI and do not use
those....... suitable for or meets....
also live by this maxim "Nothing is more expensive than to be cheap on a MB"
Click to expand...
It's a 1984 & an approval is most likely obsolete. I'd imagine there is not any oil company paying for that obsolete specification so your requirement of "Approval" is nonexistent. That leaves meets & or replacement specifications. There have been advancements in oil since then. While there probably isn't the same amount of high additives there were in 84' there is certainly better base stock in off the shelf products like T6. T6 is a diesel rated <1% Saps oil after all and with the lower additives are not going to hurt the catalytic converter on that car as originally was probably greater than >1.6% back then. Using T6 in this MB changed every 5k miles is far from being "Cheap".

revdarkwing said:
I wasn't planning on testing their warranty anyway.. seems crazy to drive a car that long without changing oil.
Would ya'll recommend full synthetic or the blended version. I've always gone full synthetic simply because I considered the blend a cheaper alternative for folks who didn't love their car as much as I did mine. Some told me that since synthetic oils weren't around when this car was build, it's best to use blended. I don't buy that theory but I also am ignorant about a lot of things when it comes to oil.
Click to expand...

Full Synthetic is more affordable & obtainable than it ever has been. Yes, synthetic's were around in 84 but they were somewhat harder to obtain. Conventional have their place & doesn't mean one using it doesn't "love their car as much as you" so throw that one in the trash. LOL Synthetics are superior to conventional oils & most 5w-40's, if that's what your after, are going to be mostly full synthetics to get the wide range 5 to 40.
 
Last edited:
I used 15w-40 T4 and just GTX Castrol 20w-50 in my old 84 300D. It had nearly 400,000 miles when the thing was basically returning to the earth. The engine was strong but the rest of the vehicle was done. I sold it for $1,200 bucks. Good body no rust. Still kicking myself.
 
We're Metals said:
I used 15w-40 T4 and just GTX Castrol 20w-50 in my old 84 300D. It had nearly 400,000 miles when the thing was basically returning to the earth. The engine was strong but the rest of the vehicle was done. I sold it for $1,200 bucks. Good body no rust. Still kicking myself.
Click to expand...
Exactly this, the Merc owners manual will probably recommend 20w50. Back in the day, passenger car oil would be rated for gas first, diesel second, something like API SF/CD. And they felt that was good enough.

T6 5w40 markets itself as ONLY a diesel oil, they gave up on gas certifications. It would be splendid for your ride. I had a couple of those cars-- the oil filter is quite a contraption and a poorly made one would make itself visible-- you can see the pleats on most of the unit. My turbo spooled up significantly quicker on cold 5w40 vs dino 15w40.

Be sure to tune up the rest of the car, in particular a valve adjustment, fuel filters, and the vacuum lines going to the ALDA (an emissions/ power lowering thing between the gas pedal and the injection pump.)
 
eljefino said:
Exactly this, the Merc owners manual will probably recommend 20w50. Back in the day, passenger car oil would be rated for gas first, diesel second, something like API SF/CD. And they felt that was good enough.

T6 5w40 markets itself as ONLY a diesel oil, they gave up on gas certifications. It would be splendid for your ride. I had a couple of those cars-- the oil filter is quite a contraption and a poorly made one would make itself visible-- you can see the pleats on most of the unit. My turbo spooled up significantly quicker on cold 5w40 vs dino 15w40.

Be sure to tune up the rest of the car, in particular a valve adjustment, fuel filters, and the vacuum lines going to the ALDA (an emissions/ power lowering thing between the gas pedal and the injection pump.)
Click to expand...
I loved it when a vaccum leak would pop up. It would kill the transmission (make it upshift super quick into the next gear), door locks and ability for the engine to shut off. I did so much work to that car over the years. Never could get the A/C to work.
That being said, nothing like the 40-60mph pull full throttle with the turbo going. I miss that car.

I think we used 5w-30 in it a few times (whatever was left over). I too noticed the turbo spool was quicker. Go figure.
 
Pelican said:
As an ex MB owner I can tell you this:
Use only oil in the right weight range with the MB Approval number, follow the recommended OCI and do not use
those....... suitable for or meets....
also live by this maxim "Nothing is more expensive than to be cheap on a MB"
Click to expand...
I'm with you on the maxim... would appreciate if you could clarify "MB Approval number".
 
andreigbs said:
Welcome to BITOG, where we tend to overthink and overanalyze.

Try and keep it simple, you will live a happier life.

That said, T6 is a great oil for your OM617. Change it annually at minimum or at no more than 10K miles if you plan to rack them up (doubtful in a 40yr old Benz).
Click to expand...
Well.. the car only has 211,000 miles on it (can't believe I just used "only" to describe over 200k on a car) so I do plan on driving it. Probably 10K a year or so.. not sure if that's racking them up or not.
 
When I had my 300D I could not afford synthetic oil for it so I went with Delvac 15W40. These days, knowing what I've learned here on this forum, I'd try super tech 15W40.
 
revdarkwing said:
I'm with you on the maxim... would appreciate if you could clarify "MB Approval number".
Click to expand...
All Oils that meet the MB requirements get a MB Approval number,(which varies with the type of engine for which it's made)
upon request & application by the Oil manufacturer. I don't know if the Oil Manufacturer has to pay for this (probably) but it's an assurance that the oil meets the lubricity & additives necessary for the long life of the engine. Since there is also the factor of older engines and MB Oils are always backward compatible, the oil manufacturer must satisfy this facet as well.
 
I run a full synthetic 5W40 or conventional 15W40 in my ‘92 300D 2.5T. 5k OCI.

A person on the W124 FB site posted that his 300D 2.5T just hit 1,098,000 miles. Conventional 15W40 and a Mann filter every 5,000 miles. 🙂
 
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