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I have read these posts on the comparison of Amsoil series 2000 75W-90 and the Lubrication Engineers 607 straight 90 weight gear lubes. Before I comment on the discussion a little background about me. (I am giving this since (name withheld) told us he was a Lubrication Consultant certified by STLE) I am an Amsoil Direct Jobber certified as an Industrial Rep by Amsoil and I have 23 years of Navy Nuclear Engineering experience. I am very respectful of the Society of Tribologist Lubrication Engineers otherwise known as STLE. I acknowledge your certification and might add that I too, should have this done in a couple of months. Now in the following discussion, I will not try to question your specific knowledge or my own. I will however, use the various references that we both recognize in our business. I will use the STLE, the Society of Automotive Engineers (SAE), the American Petroleum Institute (API), the American Society for Testing Materials (ASTM), the American Gear Manufacturers Association (AGMA) and some generally accepted knowledge. First if we are going to discuss gear lubes, then we should define what we want a gear lube to accomplish. In other words, if we don't specify what we want the lubricant to do then how do we know if it has been accomplished? So, here are the accepted functions of gear lubes (reference STLE handbook of lubrication):
Function in high and low temperature conditions Some additional characteristics we desire from gear lubes are:
The AGMA is the leading authority on gears and their lubrication. In order to simplify the proper application of automotive and truck gear lubes, the API has developed a system of classification for these lubricants using the designation ofGL-1 through GL-5, The SAE sets the viscosity scale for the auto and truck products and stipulates which ASTM tests are appropriate to certify these lubricants. This is important to keep in mind so we can use standard accepted testing and apply uniform standards to ensure we are comparing apples to apples and therefore making accurate judgments. Now, on to the comparison: you stated that the test ASTM D5707 titled SRV wear test showed Amsoil 75W-90 series 2000 to be inferior to LE 607. This test was done at 50°C (122°F) and 50 Neutons (approx 5kg) was used for break-in and 200 Neutons (approx 20kg) was the test load, frequency 50hz stroke 1.0 and specimen ball and disk. You even gave scar length and diameter of 0.59 L and 0.65 W for Amsoil and 0.20 L and 0.06 W for LE 607. You went on to say that the EP or seize part of the test showed Amsoil seizing at 300 Neutons (approx 30kg) and le 607 seizing at 1100 Neutons (approx 110 kg). First Question: Why did you use a test designed to test the galling characteristics of grease to test gear lubes? This test uses the characteristics of very slow motion coupled with extreme load to test when grease will break down and allow metal-to-metal contact. Moly fortified greases are subjected to this test to ensure that grease used in extreme loads for primarily low speed applications will meet the load needs. Additionally, the temperature of 50°C is a poor temperature to test these two specific gear lubes. The straight 90 is an ISO 220 viscosity at 40°C and the 75W-90 is only around ISO 100 at this temperature. The multigrade function of the 75W-90 causes it to thicken to ISO 220 at 100°C. certainly the Fourball wear test would be better designed for high-speed applications. Although some applications of gear lubes in very slow moving industrial applications might show some relevance to this test, there are few parallels in automotive applications. Second Question: When checking your LE website, there is no automotive gear lube number 607. The recommend gear lubes on the LE website for auto or truck applications is 703 and 704 for petroleum and 9921 or 9922 for synthetics. In fact, it becomes necessary to go to the industrial products to find the number 607 gear lube. Turns out the 607 is a straight 90 weight ISO 220 industrial gear lube. Now, this is misleading. Amsoil has a complete line of industrial oils and also has ISO 220 synthetic gear oil for industrial applications. Now here is why this is misleading:
These parameters are necessary to evaluate the complete job of the gear lube not just the anti-wear or extreme protection characteristics. The petroleum LE 607, by your own words, has about 12% more EP additive than Amsoil series 2000 75w-90. Simply put, it needs it to survive. An oil film that gets trapped between the teeth of the gears lubricates the gears. Under extreme loads the film undergoes a process called elastohydrodynamics that actually causes the metal to plastically deform. This intense pressure causes high temperatures and eventually degrades the petroleum basetocks. The extreme pressure additives must perform most of the protection of the gears due to the low film strength of the petroleum and therefore are used at a higher rate than they are in higher film strength synthetic oils. So it makes sense to load more EP additive into the petroleum than you would in the synthetic. In very high temperature situations the petroleum oil is thinning and literally vaporizing and not supporting the gear protection at all, again relying entirely on the EP additive to prevent damage. This will be revealed in the Noack volatility and flash points of the oils. Now for the low temperature performance; the petroleum is dead on arrival. Tests indicate that at minus 20°F it can take up to 22 minutes for 90 weight gear oils to start to travel up the ring gear. It takes about 14 seconds for Amsoil series 2000 75w-90 to be in full travel. The petroleum has to heat up due to friction of the gears to finally begin to move. This performance by petroleum is simply unsat in cold weather. Even multigrade petroleum is inadequate, much less a straight 90 weight. One of the other primary functions of the gear oil is to protect the bearing in the axles and the differential. There is little need for EP additives in bearings, in fact additional anti-wear additives are added to provide the bearing lubrication. You see, EP additives are basically strong chemical compounds (usually sulfur based) that, when they get hot they actually chemically attach to the metal surfaces of the gears and form a protective layer. The bearings should never get hot enough to activate the EP agents and therefore rely on anti-wear additives that are loosely attached to the bearing surfaces. These anti-wear additives are usually a type of zinc compound, which is a sacrificial metal if the film of boundary lubrication breaks down in the bearings, again you see the term of film coming into play; synthetics have superior film strengths to petroleum oils and are less reliant on anti-wear additives. Cold viscous petroleum or hot thinned petroleum will simply not provide the protection of a good synthetic gear oil. The EP or anti-wear additives must be replenished by incoming oil to maintain the protective surface they provide. If the oil is too thick to flow, then the additives on the surface of the metal are expended and wear takes place until more oil brings in new additives. When the oil is so thin from high temperature then all that is protecting is the additives; the film of oil is basically too thin to provide separation of the moving metal surfaces. |
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