| Viscosity of oil is a characteristic that parallels its ability to protect the engine. Synthetic oils generally have a higher viscosity at upper cylinder temps which is why it and castor oils are the oils of choice for high heat engines. But unfortunately some racing engine oils have what I consider too much of viscosity modifiers just to make the product look better on the specs sheet (which should show its viscosity at 40C and 100C). After using Redline Allsport which is 1/3 synthetic and 2/3 group 1 mineral oil (the worst oil) and too much viscosity modifiers, my cylinder on my air cooled engine was quickly ruined. I suspected it was due to the viscosity modifiers which to me are just chemicals to boost the viscosity but in a false way that doesn't lead to more protection and may lead to even less protection. But as usual I was absolutely alone with this idea. Google recently made its Gemini AI available for public use and I asked it about this and it responded: "These modifiers can sometimes degrade at higher temperatures, causing the mineral oil's viscosity to drop more than synthetic oil at high operating temperatures like 175*C." Wham Bam thank you maam! I thought so. Then I asked: "Due to the tendency of viscosity modifiers to degrade at high temps then are they typically more prominent in engine oils for moderate street use than in oils (motorcycle 2 stroke) made for competition?" Gemini responded: "You're absolutely right. The type and amount of viscosity modifiers used in engine oil depend heavily on the intended application. Here's how it breaks down: Moderate Street Use: Engine oils for everyday driving prioritize a wider range of viscosity across temperatures. They achieve this by using more viscosity modifiers. These modifiers help the oil flow easily during cold starts and maintain a good lubricating film at operating temperatures. However these modifiers can degrade at very high temperatures, which isn't a major concern for typical street driving. Competition Oils (2-Stroke Motorcycles): In high-performance applications like competition motorcycles, the engine operates at a much wider temperature range and often reaches much higher peak temperatures. Here, prioritizing extreme high-temperature performance becomes crucial. To achieve this, competition oils typically use: 1) less viscosity modifiers: This reduces the risk of degradation at high temperatures and ensures the oil maintains its lubricating properties even under extreme stress. 2) base stocks with higher natural viscosity: Carefully chosen synthetic, castor, or semi-synthetic base oils can provide good viscosity at high temperatures without relying heavily on modifiers. There's a trade-off though. With fewer viscosity modifiers, competition oils might not flow as easily at cold starts compared to street oils. This is acceptable for racing conditions where immediate cold performance is less critical, but not ideal for everyday use." For More Info Just go to my oils page and look at the 200C viscosities for each oil. For example Motul 800 (synthetic + 6% mineral oil) has a 3.1 viscosity and Redline Allsport has a 3.5 viscosity although it is only 1/3 synthetic. It obviously has a lot of viscosity modifier to be able to list a higher viscosity than Motul 800. Notice I have a section for oils I won't put into my oil ratio calculator due to their artificially high viscosities which includes Redline Allsport and Two Stroke Racing Oil, Klotz Super TechniPlate and TechniPlate TC-W3, and Interlube Opti-2.  High Heat Engines needing #9 or 10 NGK plug are high heat engines and should have the best oils, ones w/o group 1 mineral oil and with little to no viscosity modifiers. But personally I wouldn't use any of the above listed oils in any engine, but that's just me. I like to get the longest ring life possible, especially in this "Global Reset" economy. Allsport is probably the worst oil I know of because: 1) it ruined my cylinder after just a few miles of using it at 42/1. (it was my motorized bicycle cylinder which has weak plating. But no other oil caused that and so I think Allsport would cause more rapid ring wear on a normal motorcycle engine) 2) It has too much viscosity modifier and is 2/3 group 1 mineral oil which has a very low flash point and evaporates right off of the hot cylinder. Here's a pic of my cylinder with its plating "frictioned" right off:  Oils With Too Much VM: Amalie Pro 2T, Spectro 2T, Castrol Go!, Golden Spectro, Goldfire Pro, Schaeffer 9000, Redline Allsport, Redline Two Stroke Racing, Klotz Super Techniplate, Opti-2 |