Mercedes 126 Repair - Choosing the Right Oil

Mercedes 126 Repair - Choosing the Right Oil
By [http://ezinearticles.com/?expert=Richard_M_Foster]Richard M Foster

There are two main issues we need to worry about when choosing the best oil for our Mercedes 126. Costly repairs can be avoided if we get this decision right.

VISCOSITY

Picking the viscosity of your oil used to be a relatively simple decision, and I believe it still is. I say "used to be" because the oil companies now offer a vast array of products, many with zero- and five-weight winter ratings, and some with huge multigrade ranges. Furthermore, a school of thought has emerged in certain circles, apparently influenced by analogies from human biology, that leads many to purchase new-fangled oils that are totally inappropriate for our cars.

The theory goes that since most engine wear occurs on cold starts, we want an oil that flows freely when it is cold. Heavier oils, it is said, are as dangerous to our engines as thick blood is to a human body with constricted arteries. High oil pressure, just like high blood pressure, signifies flow restrictions and is unhealthy. While there is an obvious truth here, this thinking can be taken too far.

The oil companies have had to respond to changes in demand patterns. Modern car engines are being manufactured with very fine tolerances. The major car companies have switched to thinner oils, typically 5W-20 or 5W-30, partly because thinner oil passages need thinner oils, but also because thinner oils tend to improve fuel economy. But the engines in our 126 cars were not manufactured with these tolerances.

Mercedes tells us in no uncertain terms, in the owners manual, which oil we should be using, and the main consideration is climatological. The thin oils commonly used in modern cars would only be appropriate in Arctic climates. For the vast majority of users, the ideal viscosity is 15W-40, and that is what Mercedes put in these cars at the factory. Owners in warm climates where frost is rare can safely use 20W-50. Contrary to the modern over-analysis mentioned above, this heavier oil has proven to work wonderfully well. I am personally aware of one 420SEL that surpassed 800,000 miles down here in Florida. The owner used the cheapest 20W-50 he could find.

ZDDP

The other major issue we must consider is the strength of the anti-wear additive package. In 2007, the federal government required oil companies to reduce the amount of ZDDP in their oils. The aim of the regulatory change was to lengthen the service life of catalytic converters, as ZDDP is somewhat hostile to those devices. This zinc and phosphorous compound is a highly effective anti-wear agent in what is referred to as "boundary lubrication" situations; i.e. when high-pressure metal-on-metal contact occurs within the engine. Such contact is less of a concern in modern engines with roller cams, but older engines, especially those with flat tappets, need the protection that ZDDP provides.

Consequently, the latest API certifications - SM for gasoline engines and CJ-4 for diesels - bespeak weaker anti-wear packages. Some oil companies have attempted to compensate for the reduction in ZDDP by adding other agents such as molybdenum, but they simply aren't as effective in older engines.

Many Mercedes owners have known about ZDDP for years and found themselves drawn to heavy-duty, diesel-rated oils like Shell Rotella, Chevron Delo, and Mobil Delvac (which also happen to be the ideal weight). These oils typically had much stronger anti-wear packages than gasoline-rated oils, in addition to the detergent/dispersant packages needed to deal with the soot produced by diesels. Indeed, such oils must bolster the anti-wear package because the detergents may tend to wash the oil off internal parts. Unfortunately, even these oils were reformulated and are no longer as beneficial.

Research suggests that the optimum level of zinc is in the region of 1300ppm and the ideal level of phosphorous is about 1200ppm. Of the new CJ-4 diesel oils, the only one that seems to meet those tests is Chevron Delo 400LE. But there are other options.

If you live in a climate where 20W-50 is viable, the best option is probably one of the "racing" oils, especially Brad Penn and Valvoline VR-1. The latter is readily available at Advance Auto Parts; the former requires mail order for most people. The only drawback to these oils is that they are not intended to live in the crankcase for long periods. But since you'll be changing your oil at least every 3,000 miles, that won't be a problem, will it! Alternatively, Amsoil's synthetics have retained strong ZDDP levels and could be used for extended drain intervals if needed.

If you need 15W-40, a lesser-known but very good option is Swepco. Porsche 911 owners swear by it. But, if you can find it, diesel-rated oils that have retained the older CI-4/SL certification remain appealing. One such oil is Mystik 15W-50, sold by Tractor Supply. This oil is not well known at all outside trucking and agricultural circles, but it has a terrific specification and is very affordable.

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