Trying to select a winter oil for my 1978 300D (non turbo). I have read the various oil threads and have come away with much knowledge, but I have one specific question and would like a specific answer.

The specs on the back of the Rotella state it covers various API "C" standards as well as some manufacturers specs including "MB approval 228.31".

The back of the Mobil 1 Turbo Truck Diesel states only it "meets or exceeds light duty including Powerstroke, Duramax and Cummins". It also says "Meets or exceeds heavy duty including Mack, Detroit Diesel, Caterpilla and Navistar". It also states "Meets API SM, SL and SJ".

So the Rotella covers "C" stuff and mentions a Benz spec. The Mobil covers "S" stuff.

Which do I want. My car currently has Shell Rotella 15-40 in it. NO oil leaks other than the PCV elbow joint on top of the valve cover.

Thanks in advance, also apologies in advance if it becomes an oil Jihad

Both are excellent oils and it's doubtful that it makes any difference which one you use. Buy whichever one is cheaper.

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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

Both of the synthetics you mentioned are fine oils. The M 1 turbo diesel lists the S designations so one will realize it is fine for gassers even though it mentions diesel in it's name. The T 6 has a more extensive listing of the C specs and also lists SM, which means that it also meets SL & SJ, etc. since the S specs are progressive, i.e. SM also meets all specs with letters that come ahead of M. You can't go wrong with either.

Both are year around oils and will work just as well in Texas in the summer as in cold climates in the winter. Indeed, the 15W40 standard oil you mentioned is a good year around oil in all but the very coldest areas. If you are in a climate where you get frequent sub zero F nights you could even find 0W40 oil that would work fine year around in that harsh climate. I don't believe there is any reason for using a different oil in the summer than in the winter, and I remember a time when we used 30wt in the summer and 20wt in the winter. Very different oils, and engines were worn out at 100,000 miles back then.

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'97 E 300 D

The part of Ontario I live in gets hot summers hence the 15-40, and fairly cold winters. I got the car in thew middle of last winter and starting was annoying, it had to be plugged in for a couple hours (stock block heater) for the first morning start, and then fired up every 4 hours or so afterwards. The glow plugs were 12 year old loops and the valves had not been done for 12 years though. Valves are now being done properly, and I'm putting in pencil "conversion" plugs in the fall.

If the 5-40 weight iol doesn't make a big difference when starting I might just stay with the much cheaper 15-40, hell it will allow more frequent oil changes!

Pencil plugs will make a big difference unless you have compression problems.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

No doubt good injector and strong battery help in our Canadian winters.

I now use Mobil 1 TDT 5W40 in my 85 300D. For winter starts, it has (I believe) a much lower pour point or MRV @-40 that 15-40 oils. When you first start the car in winter, with higher viscosity oil you may not get the required lubrication, just when it is most needed.

In the USA, at Walmart, Mobil 1 seems to cost $24.97 for 5qts regardless of which Mobil 1 I buy. I usually stock up when down there in the winter. Canadian retailers just don't seem to get it!

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The 5W oils will likely give you better starting. As long as the viscosity ends in 40 it will be fine for the summer. I have used both the synthetics you mentioned. I have noticed that the timing chain etc. looks cleaner with the T-6, when looking through the oil fill hole, after standing overnight. I'm not sure what that proves however.

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'97 E 300 D

No, you don't want 15w40 dino in there in winter temperatures, unless (a) you have very good compression on at least 3 cylinders, (b) your starter, glowplugs and battery are in absolutely top shape, and (c) the car can be left plugged in with a block heater or a coolant heater (or in a heated garage) all the time on cold days.

There has been considerable discussion on this forum about the practical, extended drain intervals of the newer synthetics like T6. I now run mine for 6-7k miles (I have an ex-US car) with a filter change at 3.5k. With that sort of drain interval, the cost advantage of using conventional with shorter drain intervals disappears.

I have been driving these cars in winter since 1999 in eastern Canada. Trust me, you do NOT want 15w40 dino oil in your crankcase after the second week of December.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

All you have to do is look at how much longer it takes the oil pressure gauge to come off the stop in winter... moments for 5w40 and seconds for 15w40.

I use 5w40 year round

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Thank you for the feedback everyone. I think I'll go with the Shell T6. It pretty fracking expensive in Canada though

At the moment, Canadian Tire have 40% off sale on Mobil 1 European Formula. This includes 5W40 ESP. This is what MB specify for their modern diesels, but not what you want. Good deal for those that do:

Mobil 1 Synthetic Euro Spec Oil, 1 L | Canadian Tire

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Agreed. Wallyworld has it cheaper than Crappy Tire, though there isn't much difference when CT puts it on sale (about twice a year).

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

Both products exceed your needs.
Both products exceed all 1978 300D factory specification.

.

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