Untertürkheim

Hello fellow listers, recently I have been debating with myself about which viscosity of oil to use in my 560SEC.

I'm stuck between the Mobil 1 0w-40 and 15w-50. The car is in Los Angeles, so the weather is always relatively warm, and I drive mostly at sustained high speed on the highway.

I've heard arguments for both grades, I am just trying to figure out which one will provide better lubrication for my situation.

vettdvr

Mobil 1 0w-40

lars

If your Mobil 1 container is marked for environmental compliance, the answer is neither. If you're interested in why not, read on.

Several boards, and maybe this one too, had discussions a few months back about an article written by Keith Ansell on lubrication failures in rebuilt engines. The failures were caused by a change in the specifications for engine oil and were documented in advisories from, among others, Crane Cams and the American Association of Engine Rebuilders. My view of this article was that it sounded authorititative but lacked verification.

The current issue of the Star, the magazine of the Mercedes-Benz Club of America, carries an article by the club's Technical Chairman, George Murphy. He's done his own research and the conclusion is similar. Oils formulated for modern engines do not provide adequate lubrication for older cars.

Oil specifications are set in Europe by the ACEA and in North America by the API. Both these organizations have acted to restrict the amount of ZDDP, a zinc-based compund, in current specification oils because zinc poisons catalytic converters when the oil is burned, increasing emissions. ZDDP was present in the additive package of older formulations to increase anti-wear characteristics.

Mercedes-Benz issued a Factory Service Bulletin, S-0473-07C, last September that addresses this topic without actually mentioning it. MB defines 'older cars' in this context as 1997 and earlier. For these cars the bulletin says, in part: "Mercedes-Benz recommends the use of MB-approved engine oils...which meet ACEA and/or API classifications listed on the chart below. If a MB-approved or ACEA quality engine oil is not available, then an API quality engine oil meeting the below listed API classification can be used. Only engine oils (including synthetic) with any of the following classification grades, or combinations thereof, are approved."

The chart lists only these specifications as acceptable for gasoline engines: ACEA A3 and B3, and API SJ and SL. The specs for diesel engines are ACEA B2, B3 and B4, and API CF-4 and CG-4. Most current generation oils formulated for gasoline engines are API SM and are zinc-reduced.

The bottom line for me was that I'm going to change my practice at next spring's oil changes for my older cars. I'll be looking for an SJ/SL oil. Ansell and Murphy recommend oil formulated for diesels or motorcycles. A quick survey at my local store shows the only oil on their shelves that says it meets the SJ/SL spec also says it's formulated for four-stroke motorcycles. Other conventional alternatives include oil for high mileage engines, for example from Pennzoil. High mileage oils also have an additive package that includes a seal sweller, which can be a good thing in older vehicles. Mobil 1 says it meets SJ/SL but it's an SM oil and the formulation marked for environmental compliance is zinc-reduced.

As for viscosity, the MB service bulletin suggests you should select it on the basis of the lowest air temperature expected before the next oil change. For temperatures down to 23 and above 86 it suggests you might use something as heavy as a 15W-40, a 20W-40, a 15W-50 or a 20W-50. I can e-mail you a copy of the bulletin if you send me a PM.