Is the 0-40 too light of viscosity for the older diesels??

Absolutly Yes! Too Thin!

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.

Yes definitely! I would only recommend this if you lived in Fairbanks Alaska or Duluth Minnesota, well maybe International Falls! What you need to look for is the class/ type rating. For instance, "S" rated motor oils are for gasoline engines and will work on diesels, but burn off too soon and don't offer very good protection! You need a "C" rating and from what I've seen, one of the best out now is "CH or CI-4" with "CA" offering the least valuable qualities and "CI" offering the best that is available right now. I would be using a 15W40 CH or CI at 10 degrees above Zero and higher. 0W40 is just to thin for start up conditions and no decent diesel engine mechanic or service person recommends it right now. Hope this helps! Castrol Tection Extra and Valvoline diesel blue would both be good! Royal Purple is good if you can afford it!

A few members have use it and have been pleased with the results. I personally use a 5W-40 from Ams oil.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Is that Ams oil marked as diesel specific? They had some 5W 40 in one of my local shops today but it isn't marked like the other brands as being diesel or not.

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1982 300TD 210K miles ("The Replacement" aka "The Anvil") - SOLD
1979 300SD 245K miles (never ending project)
2007 Pinarello F3:13
1995 Ducati 916 (SOLD, sniff)
1999 Ducati 900SSie (SOLD)

The stuff I'm using is diesel specific. https://www.amsoil.com/storefront/SearchResult.aspx?CategoryID=368

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

IMHO, M1 0W40 is thin for a old diesel. I use M1 5W40 in my 616 and 617.

Works fine, its been running in our '83 SD for almost 5,000 miles so far and the engine is way smoother than it used to be, and cold starts are instant. I use the 5w40 in my car, as soon as autozone carries it in stock here I'll be using it in both cars. See sig below for oils used in cars.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Can the viscosity cause an increase in oil consumption...like 0-40 cause more oil consumption than say 15w-50 motor oil?? Some people I've talked to say it doesn't matter.

Ours don't seem to use anymore than before....usually less than a quart over 5000 miles, was probably about the same when we ran 15w40 rotella dino oil, but I also changed that way more often (every 2500-3000miles)

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I am really impressed. You have over 250K on those cars and they use less than 1 quart of oil in 5000 miles. That's really awesome.

Everything I've seen says 0W-40 is just fine to use in the OM61x engines.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

The 0W-40 might be fine, but I wouldn't recommend it for an old diesel and I'm speaking from personal experience. I tried it once in my ex-82 300D with over 200K miles and the cold idle instantly became rough whereas before on a 15W-40 oil it was smooth. I wouldn't go any lower than 5W. I use 5W-40 Red Line oil in all of my current cars and they seem to like it. According to the Amsoil monthly magazine, Daimler now recommends 5W-40 for all their new diesels, in addition to 0W-40.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

The Mobil 1 site recommends 0-30 for cold weather and 5-30 for warmer weather. I'm using the 5-30 year round in denver. Works just fine. I would imagine the Mobil 1 people would have a fairly good idea as to which of their oils would be correct. I'm thinking synthetic 0-30 would be a much better oil than 25 year old 15-40 dino oil as was originally designated. my 2 cents

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Kevin
82 300D

You may want to check that, the M1 site recommends 5W40 turbo diesel truck for your car:

http://www.mobil1.com/usa-english/motoroil/car_care/which_oil/WhichOilOption2.aspx

You don't want to use xW30 above 77 F ambient, according to the owners manual.