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Old 10-10-2017, 03:08 PM   #1
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Join Date: Apr 2007
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Default Old Cars and New Oils What to Use

First, a little background to make sure everyone is on the same page.

Most motor oils produced through the early 1930s had little or no additives. In the early 1950s, the so-called “MS” sequence engine oil designations were developed, including API (American Petroleum Institute) ML (motoring light), MM (motoring medium) or MS (motoring severe). These oils were finally defined in the late ‘50s by sequence tests that measured resistance to corrosion, wear and oxidation, as well as deposit control.

At the time, the original equipment manufacturers also had their house brands. There were concerns that these designations were too broad and made it difficult to tell whether or not an oil was really suitable for use in a particular engine.

Around 1970, the API’s “S” categories came into force to make it easier to identify the performance level of the oil. API started with SD for the then-current oils, moving through the alphabet to today’s SN oils. It designated earlier oils (SA, SB, and SC) as obsolete.

The question of the proper engine oil is more complex than you might think. It depends on how old the car is and the kinds of engines that were available when it was made. It seems like the “common” recommendation at that time was SAE 30 in the summer and SAE 10W or SAE 20W20 in the winter. (Please note that the OEM recommendations were made before the advent of multi-grade engine oil. Multi-grade oils provide much better protection against wear, especially at start-up.)

Things moved along without too much difficulty until the advent of lower zinc dialkyldithiophosphate products. This occurred around 2000 with the introduction of API SJ which limited the amount of phosphorous in the oil to a maximum of 0.10 percent by weight. The driver behind this was protection of catalytic converters. Phosphorous tended to poison the catalyst and make them non-functional. Prior to API SJ, phosphorous in engine oils were about 0.12 percent, and in some cases even higher.

After these oils hit the market, classic cars began to have wear problems. The specific problem being that vehicles with a flat tappet design needed a higher phosphorous level than the available SJ oils provided, in spite of the API guidance that each category of engine oil would be backwards compatible with earlier categories.

A flat tappet in the hydraulic valve lifter assembly makes contact with the cam lobe and can result in some significant wear. Enough phosphorous will minimize this problem, and the necessary level seems to be around 0.12 percent. API SJ oils were low in phosphorous, which most mechanics refer to as “zinc,” since that is the source of phosphorous in engine oils. There were rumblings from classic car groups concerning the change.

API SL and ILSAC (International Lubricant Standardization and Approval Committee) GF-3 retained the lower level of phosphorous, but API SM/ILSAC GF-4 upped the ante by lowering the phosphorous limit to 0.08 percent by weight. This is the point at which the classic car folks became really upset. They wanted an oil that would protect their prized cars, but that, for the most part, wasn’t available.

Many OEM engine folks believe the evidence is overwhelming that there is not enough ZDDP in GF-4 and GF-5 oils for older engines with flat tappet cams. Some classic car guys did not reach 200 miles on high-dollar rebuilds before rounding off a couple of cam lobes, and other suffered early mileage cam failures. So we know that a lack of sufficient ZDDP leads to wear problems in certain car engines. The bottom line for classic car enthusiasts is to make sure you are using an oil with the proper level of ZDDP.

ZDDP actually has several functions in engine oil besides Antiwear. It also performs as an Antioxidant and minimizes Corrosion through its surface reaction. The bottom line is that most engine oils with the API designations of SJ, SL, SM and SN contain a much lower amount of ZDDP in those oils to give adequate protection for engines which have flat tappet cams.

One of the exceptions is the SWEPCO 306 engine oil in 10W30, 15W40 and 20W50 weights which are listed as API SL/CI-4 and have a high zinc content. SWEPCO continues to produce those oils for customers who need the extra protection, both for early gasoline, diesel and race-proven requirements. Keep in mind however, that it DOES NOT MEET the requirements of low ZDDP content for equipment calling for API SM or SN. They do manufacture other products for the current, later model cars and trucks which meet all those needs.

IHPA has used and recommended SWEPCO 306 for over 10 years, and it is available for sale through their website, or pick-up at their location.
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