In my garage there rests a jug of Mobil 1 15W-50 which I bought two months ago intending to use in my Bimmer, which has been garaged since my daily driver's become a 300DT two weeks ago.

The 300D really needs an oil change, and I'd like to do it this afternoon or tomorrow. The question is, should I use the 15W-50 or get some turbodiesel oil from the truck stop? And on the same subject, should I be using synthetic or dino in a 617 which has been running dino its entire life, and hasn't had its rubber changed in ages? It's currently running well enough, albeit a 1qt/1000mi leak, that it'd kill me to start a lot of other leaks by unclogging sediment with synthetic -- if that isn't just an old wives' tale, that is. If it isn't, she could sure benefit from any advantages synthetic provides. I'm going to be driving in 100+F weather all summer.

Mobil 1 15w50 is just fine.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

john, do you have enough 15W50 to perform a complete change? The old product carried several specific diesel ratings. They've re-formulated and the new 15W50 doesn't carry the rating it used to.

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1998 W210 diesel (wiped out by a texter)
Baum spring compressor "for rent"

Aha! I thought it was a jug, but it's four quarts. Rear panel reads:

A3, B3/B4
API SM/CF
API SERVICES SM/CF
SAE 15W-50

According to Mobil's site, while 15W-50 "also meets the requirements for diesel powered vehicles where an API CF or CD oil is recommended," Turbo Diesel Truck 5W-50 "Meets CI-4, CH-4, CG-4, CF-4 and CF."

Do the ratings matter with 617s? I think I'll risk one more day to nose around for the 5W-50 and save the 15W.

As long as it is CF rated its fine.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Ace! Thanks.

API CF = non-EGR equipped diesel engines (not the best solution, IMO)

believe consensus here on this site is to change out the oil filter after say 1000 miles when switching to synthetic oil.

The EGR should be broke anyway. Its light duty, but our engines are light duty diesels. Very few of us really push the limits of that CH-I rating.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

LOL, I like it

I've seen a few UOA from these diesels and the soot content can be quite impressive.

If I understand you correctly, you're losing a quart of oil per 1,000 miles. At nearly $5 a quart for syn, that would be big $$$ leaked onto the highway between oil changes. I love syn (use 5w-40 in both my oilburners). But with an oil sieve like your 123, I'd stick with dino.

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'91 300D 2.5 Turbo 330K
'00 VW TDI Golf, 190K
'67 BMW R50/2
'73 Norton Commando Interstate

I agree, good oil.