THREE IN THE BANK, NOT COUNTING ADDITIVES
Today, the market offers oils with unusual additives - molybdenum disulfide or graphite. Their merits
and we decided to evaluate the flaws.
We now know almost everything about antifriction and antiwear additives that we are offered to introduce into motor oil on our own (see ЗР, 1999, No. 10 and ЗР, 2000, No. 2). And what to expect from the oils themselves, in the composition of which such additives were introduced by the manufacturer? How much more effective are these oils against friction and wear? Finally, what is the flip side of the coin - do unusual additives give a side effect?
Meet me. The first sample of “unusual” oil is Liqui Moly MoS2 Leichtlauf with molybdenum disulfide (photo 1), the second is Marly Black Gold Carat with graphite (photo 2). Both additives should reduce friction and wear. Well, check it out. That's just what unusual oils to compare with?
Fulcrum. It is difficult to manage without a fulcrum or reference point. In our case, without a sample for comparison.
Both test subjects - Liquid Moli and Marley - have a temperature-viscosity range of SAE 10W40 and meet the highest quality group according to API SJ / CF and ACEA A3–98, B3–98 classifications. Both are semi-synthetic. Therefore, the “ordinary” oil, with which we will compare them, must satisfy the same requirements. Here it is: “Elf Competition STI” in photo 3 is of the same highest quality class API SJ / CF, ACEA A3–98, B3–98, with the same temperature-viscosity range SAE 10W40 and also “semi-synthetic”. We’ll immediately agree: our “ordinary means” will not be subconsciously attributed to the bad ones or those who live out their lives: “ordinary” means as good as the subjects, but not containing “unusual” additives.
THINK GOOD … Let's see what we expect from good butter. To begin with, it should be well lubricated. That is, to separate the friction surfaces with a layer of oil and minimize their friction against each other. If the layer of oil is “hardy” enough, the protrusions of the microrelief will less touch each other and the parts working in the engine will last longer. All this is called the tribological properties of the oil.
High-temperature deposits are inevitable in an internal combustion engine. The ability to wash them off is one of the most important properties of motor oil - washing. But it is not enough to wash off, washed away sediment particles must be crushed (dispersed) and destroyed. Dispersing properties are responsible for this.
Well, if, after working for an hour or two, the oil will become worthless? To avoid this, a reserve of alkalinity is required, which determines the ability to neutralize the oxidation products that are formed during operation. It is also obvious that the "base" of the oil must be resistant to thermal decomposition.
Experts would certainly add a dozen requirements to this list, but our task is to compare oils according to their basic functional properties, without delving into the scientific jungle. True, one important addition is still necessary. Since our products are not quite ordinary and contain solid particles of anti-wear additives, it will be necessary to require that these particles do not precipitate and do not collect polymerized oxidation products around themselves. Simply put, so that clots do not form. We call this property stability and finally begin to check.
THERE IS GOOD, WHERE NO FRICTION. First, we evaluate the tribological capabilities of “unusual” oils. To check the anti-friction and anti-wear properties, we will use the qualification assessment method adopted by the State Standard using the SMT-1 friction machine.
The antifriction properties here are determined by the moment and coefficient of friction, as well as by the temperature of the oil in the friction zone. Anti-wear properties are estimated by the weight loss of one of the rubbing parts - a special cast-iron pad.
The result of the verification of the three samples is in the table. Compared to “ordinary” oil, the introduction of graphite allowed the “Marley” sample to reduce the temperature in the friction zone by one degree, leaving the coefficient of friction unchanged. In other words, the antifriction properties of the oil with the introduction of graphite are almost unchanged. But anti-wear properties have changed markedly and for the better. The wear of one of the rubbing surfaces when working on oil with graphite decreased by 15.8%.
Now is the turn of Liquid Moth. This “unusual” oil did not disappoint either: the temperature in the friction zone decreased by 53 degrees, and the friction coefficient - by 31.9%. As you can see, the antifriction properties are high. Antiwear too. The wear of a standard cast-iron block was 21% less than that of a “regular” oil. Good!
A DROP IN THE SEA. Can you learn anything about the quality of the oil with just one drop? It turns out that something is possible. This is called the “drip test method.” On a sheet of special paper, vaguely reminiscent of a blotter, drip one drop of each sample. When the oil completely spreads and absorbs into the paper, they begin to evaluate, firstly, the diameter of the spot, and secondly, the number of concentric circles. We explain: some additives, although dissolved in the product, are not always able to spread as far from the epicenter as the “base” of the oil. Spreading to a lesser extent, they form spots that are slightly different in color. Thus, according to the number of concentric circles and their relative sizes, experts judge the potential destabilization of the oil: what additives and how soon they can precipitate or form unwanted clots (agglomerate).
A test of the test samples using the drip test showed that the “ordinary” oil gives two concentric circles, the largest of which has a radius of about 2 cm. Two “unusual” oils spread only 1.6–1.7 cm from the center and formed three concentric circles. So there is still a “downside” to the use of “unusual” additives: these oils will have somewhat worse penetrating power and will be more prone to delamination. The latter circumstance led to check what will happen to the oils as they age.
OLDNESS IS NOT JOY. Long-term operation of motor oils in the engine leads to their aging. Deterioration of properties is manifested in almost everything: the temperature-viscosity range, washing and reducing ability change, and the optical density increases (see ЗР, 1999, No. 4). In laboratory conditions, this process can be modeled using standardized methods developed for this. So we did, simulating the aging of the oil, equivalent to triggering 60-80% of its full resource in the engine. The result was in line with expectations (see above). Both “unusual” oils have a slight precipitate. The Liquid Moths have a slightly smaller one. The Marley has a slightly larger one. Pundits call this the colloidal destabilization of oils.
"DO NOT BOTTLE ON THE HAIRDRESSER!". In order to at least a little understand what is happening, for a moment we turn to the basics of theory. An attempt to finely “grate” graphite or molybdenum disulfide and pour it into the oil in the form of a powder will lead to a complete fiasco. Both substances are insoluble in oil and will simply float on its surface. If you try to drown, they will settle at the bottom. Therefore, to introduce such additives into motor oil, they are previously dissolved in special surface-active substances (surfactants), which can capture solid particles and simultaneously bind oil molecules. Only such a colloidal solution can be added as an additive. However, as the oil ages, the surfactants contained in it lose their properties, and once solid particles bound by them precipitate. Here it is - colloidal destabilization. But the most unpleasant thing is that these same surfactants can capture not only the powders we need. Much more willingly they cling to water or gasoline that has fallen into the oil. A special check showed that the ingress of 2% gasoline or water into both oils after 5 days leads to an increase in the optical density of Liquid Moli by 9-10%, Marley by 35-40%. These values are not so great, therefore they should not frighten anyone, but they should alert …
BEST THE ENEMY OF THE GOOD? Is it possible that the high percentages of reduction in friction and wear that are completely crossed out by the negative consequences of the introduction of additives? Let's not rush. Both samples, despite being prone to delamination, are certified to meet API and ACEA requirements. Moreover, they correspond to the highest quality group. This means that they passed the necessary tests on the engines, they did not clog the filters and did not put off any deposits that frightened anyone in the oil system. So long live oils with particulate matter? Again, we are in a hurry … There are no experiments in the certification test program with the addition of water or gasoline to the oil. And the engines used by Europeans are not very inclined to fill the crankcase with gasoline. So what to do, buy "unusual" oils or not? We offer the reader to answer this question independently. We are sure that among you there will be fans of similar oils and their opponents. Ultimately, the choice will depend on your personal preferences and, sorry, the thickness of the wallet.
1. "Liqui Moly MoS2 Leichtlauf" (Liqui Moly MoS2 Leichtlauf) with the addition of molybdenum disulfide. Semi-synthetic. Specification: SAE 10W40; API SJ / CF; ACEA A3–98, B3–98. Price - 180 rubles. per liter.
Compared to “ordinary” oil, it showed a decrease in friction by 31.9% and wear by 21% with the worst penetrating ability and tendency to early agglomeration. Precise adherence to replacement intervals is desirable.
2. “Marly Black Gold Carat” (Marly Black Gold Carat) with the addition of graphite. Semi-synthetic. Specification: SAE 10W40; API SJ / CF; ACEA A3–98, B3–98. Price - 160 rubles. per liter.
Compared to “ordinary” oil, it showed a 15.8% reduction in wear and tear of inferior penetration and a tendency to early agglomeration. Precise adherence to replacement intervals is desirable. As you approach the end of your life, look at the oil pressure gauge.
3. "Elf Competition" (Elf Competition STI) without the addition of particulate matter. Semi-synthetic. Specification: SAE 10W40; API SJ / CF; ACEA A3–98, B3–98. Price - 145 rubles. per liter.
Alongside the “unusual” competitors, the honor of “ordinary” oils was adequately defended. Without “special” additives, it showed greater wear and a coefficient of friction, but at the same time it has better penetrating ability, is NOT prone to agglomeration or sludge formation, does NOT threaten troubles in violation of the replacement frequency.
The effectiveness of molybdenum disulphide and graphite additives depends on their particle size. Too small particles (1) completely “fall through” into the hollows of the microrelief and turn out to be ineffective, allowing rubbing surfaces to contact along their protrusions. Larger particles (2) are more effective, but in solution they are less stable and prone to sediment formation. In gear oils less prone to high temperature oxidation, agglomeration, or the precipitation of “unusual” additives, will be less noticeable. In addition, here the sediment will not cause clogging of the filter, as it can happen in the engine. The effect of particle size will also determine the different effectiveness of additives on different surfaces: material, heat treatment, etc.