Dr Jay’s Tech Topic of the Month

Motor Oil is Motor Oil right?                                           

Question: Is an internal combustion engine an “engine” or a “motor”? Why is it called “motor oil” if we use it in our engines? The world may never know the answers to these questions, (I personally use the words interchangeably for a device that converts energy into work- but that’s for another story). What we do know is that there are many different types of motor oils out there. Some are synthetic, some are petroleum, some blow up in Mustangs on TV commercials, others drench unsuspecting cars from the sky like an oil rain cloud. And what is with all those different numbers 20W50, 5W50, 10W40, 80W etc.  Well this month we will discuss these things ultimately to get to the point: Why you should never use an Automobile Engine Oil in your Yamaha.

Amazingly enough, a modern “Motor Oil” is not all Oil. It is comprised of many different chemicals all designed to do a specific job. There are detergents, dispersants, emulsifiers, friction modifiers, viscosity modifiers and tons of other stuff in every bottle of oil. In the early days, around the turn of the 20th century, motor oils were mostly all oil (almost no additives), straight weight refined light crude oil.  Engine requirements were fairly simple and the low power of the day meant that these oils would do a good job running along at 100 rpm. One of the first problems encountered with early oils is actually the same problem we have with oils today- TEMPERATURE STABILITY.

In the earliest days, it was cold weather. As the earliest oils cooled to near freezing, they radically changed to a paraffin substance (like wax!) Could you imagine starting up your tractor in near freezing temps only to have no oil pressure because your oil had turned into wax? Those who live in freezing climates today can use engine pre-heaters to combat this problem. The other side of the temperature stability problem is the added heat as a result of greater engine output. As engines became more powerful, oils were subjected to higher and higher temperatures and the oils started to break down (becoming thinner and thinner) until there was no film strength left and the parts being lubricated failed.

Thus entered the Polymer to save the day! The Polymer is used in motor oils as a viscosity- or thickness- modifier. Oils can still freeze, but the polymer molecule really helped to stabilize the high temperature today’s oil sees. Think of a Polymer as a tightly wound ball of string or wool and as this ball of wound up string gets hot, it expands, unwinding in the process. As more heat is applied, this ball grows and unwinds some more and grows some more. As it heats it gets bigger and bigger taking up more space, in the process making the oil thicker as it gets hotter! Pretty amazing huh? Now we see the first signs of the ability to make an oil that can be more thermally consistent. But how do they measure this? Well now on to those numbers on the bottle of oil.

Founded in 1905, one of the first priorities of the SAE (Society of Automotive Engineers) was to develop a standard for quantifying Motor Oils. They decided to range an oils ability to flow or remain viscous at two temperature extremes, 0?C (32?F) and 100?C (212?F). These temperature ratings are labeled on our oil bottles today. In a 10W40 for example, the first number and letter “10W” means this oil flows like a 10 Weight oil at 32?F (the freezing point of water). A 5W oil is even thinner at freezing, flowing like a 5 Weight oil. The second number “40” means at 212?F this oil flows like a 40 weight oil. The really amazing thing about this hot/cold ability oil has is that as the oil heats up, it gets thicker- and when it cools it gets thin again! That Polymer is an amazing molecule!

Unfortunately, that Polymer we need and love can be the Achilles Heel in our Motorcycles. In automobiles, the engine is separate from other drive train parts- and is lubricated separately. The automobile engine oil lubricates just engine parts. Automobile transmission oils (like ATF for automatics) lube the transmission clutches and Gear (Hypoid) oils lubricate the manual type of transmission and final drive gears. Our motorcycle drivelines are lubricated with one oil- our engine oil. The problem is that Automobile Engine Oils use a brittle Polymer that tends to get smashed by our transmissions and clutches. This smashing or “breaking” of the polymer is what yields the term “oil breakdown”. When the oil breaks down the polymers can no longer do their job and shortly after, the parts will start to fail.  Our motorcycles would really like to have three different lubricants, one for the clutch (like an Automotive ATF or automatic transmission fluids), a Hypoid or gear oil to lubricate our transmissions and a regular motor oil to lubricate the engine components. Motorcycle specific oils are designed to prevent this breakdown of the polymer by employing very flexible polymers that can absorb shock and shear much better than automobile oils. These polymers are more expensive to use, so Motorcycle specific lubricants cost more than equivalent automotive oils.

So, the next time you change your oil, be sure to use an oil that is specifically engineered to do the job it is supposed to. We use and recommend Yamalube oils as they are specifically designed for your Yamaha.

Remember that other TV commercial “you can pay me now or pay me later”….

Next Month: Synthetic vs. Petroleum oils

 Have a safe ride!

Dr Jay