We are changing the oil in our 95 e-350 7.3L power stroke diesel short bus. The bus has 218,430 miles on it. The guys at napa auto reccomended Delo 400LE heavy duty motor oil SAE 15W-40 for our vehicle. We were planning to buy a full synthetic like Mobil 1 because someone told us that was the best however now we are hearing otherwise.. That we should not run a synthetic oil in a diesel engine with high mileage. So I wanted to check in with what folks here at the forum have to say on the subject and if anyone could explain WHY we want to use one oil over the other.
Thank you!

 

You want to make sure whatever you buy is rated for diesel use. There multiple choices
Delo 400
Motorcraft
Rotella
And so on
If you are traveling quite a bit Rotella 15-40 is widely available and is what a lot of people, including myself, run in their trucks and mine is at 290k miles and still running strong. I personally don't care for the Delo.

 

Whether to use synthetic is strictly an economic decision. The whole "synthetic in a high-mileage engine" question is a thing of the past. It had some merit back in the '80s, but synthetic oil formulation and engine design have both made it a non-issue anymore. So it's really up to you, whether you want to spend the extra money on synthetic. It is a better lubricant, and is esp. more stable in engines like ours, that use the oil as hydraulic fluid as well as lubricant. It also flows better in cold, so where you intend to drive the bus will play a role.

 

Because of the engine design, our oil change intervals are not as long as some vehicles. Thus, I would not consider the use of higher-cost synthetics. Shell's 15W40 Rotella T is what I use. Just yesterday, I picked up some at WallyWorld and put 14 quarts of it in my Beast along with a new Motorcraft oil filter. She thanked me.

 

^^^^^ True if OCI were the only distinguishing factor between dino and synthetic. It's not, as anyone who's poured out dino 15w40 and synthetic 5w40 at -20F can tell you.

 

I use Rotella T6 synthetic. 7500 oci with uoa to support it. Based on the report I can likely go 10k miles but I don't put many miles on my truck so I am already at 18 month intervals. I'd rather not go longer.

Richard