I noticed that Mobil recommends 0W-40 for the W123 diesel motors but since it has a lower diesel spec than 5W-40, I emailed Mobil asking which one was really better. It took a couple of tries before I got something other than the blanket answer of either would work. Here is the response that I got:



Ron,

The Mobil1 Turbo Diesel Truck 5W40 motor oil would have better soot control and be the best choice for diesel engines, drain intervals would be the same.

-MJ


Ron wrote:
> I know that either product meets all of the requirements for the
> engines, but which one would protect the engine better or have the
> longest oil change interval? Will one or the other handle more soot
> loading? Would there be any difference in deposits in the combustion
> chamber?
>
> Thanks,
>
> Ron
>
>
> -----Original Message-----
> From: ExxonMobil [mailto:mobilproducts@ourdataworks.com]
> Sent: Tuesday, June 09, 2009 10:36 AM
>
> Subject: (no subject)
>
> Ron,
>
> Either product can be utilized can be utilized in both of these
> vehicles without issue, they meet all the requirements for the older
> vehicles that you have listed. So it may very well come down to what
> is easier for you to locate and purchase. The Mobil1 0W40 motor oil
> meets API "SM/CF"
>

__________________
Ron Schroeder
'85 300 Turbo Diesel 2 tank WVO
'83 300 Turbo Diesel 2 tank WVO
Some former WVO vehicles since ~1980:
'83 Mercedes 240D
'80 Audi 4000D
'83 ISUZU Pup
'70 SAAB 99 with Kubota diesel
'76 Honda Civic with Kubota diesel
'86 Golf
Several diesel generators
All with 2 tank WVO conversion
LI NY