I have always used Rotella 15-40 in my 300SDL but am thinking of going to Mobile Synthetic 5-40 truck Diesel year round here in Texas Is there any downside other than price? Also do I need to change the hoses that go to the engine oil cooler? Thanks

IMO I'd stick with what has been working very well. Also, look at the owner's manual to see if the 5W is within the climate/temp spec for your region. If not then I wouldn't use it.

As for changing the oil cooler hoses due to the switch to synthetic, no it isn't necessary. Change them if you see a problem with them such as seepage, abrasion or deterioration.

Good luck and report back with results if you decide to change oil type.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Great oil...no downside. In all likelihood you could extend drain intervals.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

If you are going to try a synthetic you might do some info searching on Rotella's T6. One of the downsides of using a synthetic is sometimes a leaky seal will flow more synthetic.

I've recently switched to the T6 but still am thinking of sending in a few oil samples for testing. From what I've read most of the more popular oils are very, very, close in performance ( supposedly proven by long history of oil testing ). Previously in my gasoline cars I used Mobil 1 exclusively, but from my reading T6 is better for diesels. Also I don't believe in going much above 5000 mile change intervals for synthetic.

But then again you can't argue with the guys that have driven a 1/2 a million miles using non-synthetic.

On drain intervals the only way to know for sure is to do an oil analysis. On my OM602 I have confirmed that I can easily go 10,000 miles.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Any modern oil that meets your mfg's spec will work just fine.

If you're going to extend your oil drain intervals, establish your new interval with use oil analysis. My understanding(for IDI motors anyway) is that soot loading is the limiting factor for oil life, and dino vs. syn makes no difference there.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

Go with Delo 400 LE 5W - 40 good stuff.

Woah wait 10k miles on an old diesel? Maybe if an oil analysis says it's ok.

I have discovered that 5W - multi viscosity oils tend to weep out a little bit faster .

My Brother swears my Mobil 1, his car seems to be fine with it, it's always an oily mess but then so it any vehicle he owns .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

My reason for going to the Mobile 1 is that a jobber friend gave me about 50 gal of outdated oil so the price is right. I do NOT plan to extend the change interval past 5K. If you want the best synthetic use Amsoil in my opinion. If you are driving a high horsepower gasoline muscle car use their Z-Rod which has higher ZPPD. Thanks for all of the replies. At 90K I have changed every hose except the oil cooler lines which look fine. My 87 300SDL went 386K on the original oil cooler hoses because I didn't know any better. I would still be driving it today if I hadn't stumbled on this 86 300 SDL with 65K milage. It still had the fiberglass underbelly pan in place.

Oil specifications change and old oil no longer meets the latest spec, but it doesn't go out of date or go bad like milk. 50 gallons of free oil that meets spec for my engine? Yes please.

Here's Blackstone Labs' opinion on the matter:

https://www.blackstone-labs.com/Newsletters/Gas-Diesel/July-1-2017.php

As long as the oil meets spec for your engine, the difference between oils is happening in your wallet, not in your engine. Chevron, Amsoil, Rotella, Mobil 1, as long as it meets spec it's all fine.

I have T6 and Delo 400 CI oil and Chevron and Havoline SI oil in stock right now. They came on sale or rebate, I bought it cheap and stacked it deep. It'll all work well.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap

FWIW, they age out not wear from mileage so you're courting disaster by not changing them in advance .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

shell helix hx7 5w40 mb 236.1 is what I use.

Several years ago AutoZone was running a special on Mobil 1 turbo diesel truck… 12.99 a gallon. I think I picked up about 45 gallons!

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

I remember that sale, I stocked up as well. Was only ~12 gallons or so in the area I was willing to drive around to, but I bought it all and would happily do so again.

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617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap