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Synthetic oil: one-size-fits-all?

Synthetic oil: one-size-fits-all?

Synthetic oil: one-size-fits-all?

So this European oil maker states that its synthetic oil can work properly in both: Otto and Diesel engines (automotive applications). It states having many decades of experience to back its product.
Even further, it claims that this oil can work safely with almost any popular fuel (CNG, diesel, gasoline) and deal with their different combustion nature and by-products. The only one difference should be the service life of the oil.
I was Googling them, verifying their reputation, and they look reputable.
I have to say I'm not a chemical engineer. I' a mechanic.

So just for curiosity I send a sample of new, fresh oil to the lab. The only one different thing I noticed is an increased level of Ca (almost 3000 ppm).
TBN value was fairly normal (11.4 mKOH/g) compared to the mineral-based oils.
But lab technician was honest and said that his method for analyzing TBN was not suitable (carbonyl-based reagent), since this is an synthetic oil. Suggested to look for a lab with "potentiometric method" for properly analyze TBN.

Finally, I found a reputated lab with such "potentiometric method" for synthetic oils, but it is expensive.
My goal is to trace a proper synthetic oil baseline in order to run a program of oil analysis for a small fleet running on stock, dedicated, stoichometric-mixture, CNG engines.

Two questions:
1. Is it correct to analyze the synthetic oil TBN with potentiometric method (ASTM 2896)?
2. New synthetic oil are, in fact, this good? I mean: one oil can work with different fuels?

Any positive comments are appreciated!

RE: Synthetic oil: one-size-fits-all?

The TBN more or less is a indication whether the oil is capable of neutralizing acids. The test was originally developed to test fresh oil on the lubricant plant as a quick check whether the additives needed were really added in the amount planned. The test since then has been very often used on used diesel engine oil - especially in those times that diesel fuel contained quite a lot of sulphur. The lowering of the TBN during service was seen as a method to detect whether there still was enough acid neutralizing capacity in the oil. That worked quite well, because in those days sulphur was by far the most important reason for the lowering of the TBN. Nowadays the TBN of diesel engine oil is far lower - as is the amount of sulphur in the fuel.

Given the fact that nowadays diesel fuel contains very much less sulphur then 20 or more years ago, a high TBN oil no longer is necessary and it is quite possible to formulate a engine oil that suits both gasoline, LPG or diesel fuelled engines in passenger cars. European oil specs as issued by ACEA or European manufacturers are based on a range of tests in engines running on various types of fuel (diesel, gasoline, LPG, fuels containing alcohols or biological components) and are capable to lubricate modern passenger car engines with extended service intervals. They need not necessarily be "synthetic" - quite a few are not but are still meeting the test requirements. The synthetic part however becomes more important when specific low temperature requirements need to be met or when very extended oil drain intervals are wanted.

Oil requirements for passenger cars are quite a bit more severe for European cars then US products and that is reflected in the specifications that need to be met. For that same reason both Ford en GM do specify different oils for their European products, and those oils meet both diesel and gasoline engine requirements.

RE: Synthetic oil: one-size-fits-all?

1. ASTM D2896 is fairly common to analyze engine oils, though there are other methods to quantify TBN as well. A TBN of 11.4 is fairly normal for a diesel engine oil. The TBN is reliant entirely on additives, so synthetic and petroleum oils won't have any difference when using the same additive components.

2. Yes, one oil can certainly function across various engine types, though it probably wouldn't be the "best" choice for any of the individual applications. It being synthetic is not a factor in how well it handles the different engine/fuel types. Aside from the extreme low temperature and extreme high temperature, the protective qualities of petroleum and synthetic oils are not reliably different from one another. The extreme temperatures are uncommon at best and generally won't happen in normal operating conditions except for special circumstances or applications.

Andrew H.

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