The best way to start a fight in any motorcycle forum, group, or email list ever, is to start talking about motor oil, and ask what oil is best. That’s probably why so many people turn to Google, or their poorly-informed friends, where they may or may not find the correct answer.
We here at RideApart have been collectively riding and fixing motorcycles for a whole bunch of years, so we’re going to try to clear up a few misconceptions when it comes to motor oil, give you the run-down on what’s what, and try to steer you in the right direction.
First, we’re going to assume (I know, I know) that you know the basics about how to change your own oil, that you should absolutely do that on the regular, why oil filters are important, what crush-washers are and all that jazz. This is about motor oil.
What Is Motor Oil Anyway?
Most motor oil, and yes, even most of the stuff labeled “synthetic,” begins as crude oil that’s pumped out of the ground. It’s called “fossil fuel” because it’s made out of really, really old dead things and the term “fossil” is a convenient slang for old stuff (It’s not actually made out of mineralized fossils; that’d make a terrible lubricant).
Tons of organic material from millions of years ago squished down and, under the correct conditions, turned to liquid-ish goop underground. That stuff is pumped out of the ground as “crude oil” and sent off to a refinery, where it’s turned into things like gasoline, kerosene (and other fuel oils like charcoal lighter and lighter fluid), motor oil, bearing grease, petroleum jelly (yup), wax, and bituminous concrete (that's asphalt). Each of these products comes from crude oil through a different refining process.
How Is Synthetic Motor Oil Made?
Your synthetic motor oil, more than likely, starts its life as crude oil. Conventional motor oil (some folks call it “dinosaur juice,” ew) does too, but its refining process is slightly less, erm, refined. The stuff that is eventually labeled “synthetic” has had absolutely everything pulled out of it except the specific molecules the oil company’s scientists have figured out make good motor oil.
Think of it this way: your regular motor oil, on a molecular level, is made up of a bunch of different-sized ball bearings with some tiny rocks and other junk in there. The rocks and junk aren’t big enough to cause problems, so it’s not cost-effective it to pull them out. The synthetic stuff, though, at that same molecular level, is all the same and same-sized ball-bearing, sometimes with some extra fancy additives that make it even slipperier. In a nutshell, this is why synthetic oils are more expensive: more effort goes into that process.
Some oil manufacturers do not start with crude oil and their synthetic oil truly is synthetic, but the raw chemical materials and the processes by which they formulate their product are proprietary and therefore extremely secret, because, you know, competition.
What's The Difference?
When it comes to viscosity, manufacturers of conventional oils use additives that help the oil stay thin so that they flow when cold, but maintain their lubricative properties when hot (that’s the viscosity rating, e.g. “10W40” where the "W" is for "Winter" and is a shorthand for its viscosity when cold). Synthetic oils, on the other hand, are chemically formulated from the outset to have a given (cold and hot) viscosity: it is engineered into the process instead of souped-up at the end.
What does all that mean? The additives in conventional oil can vaporize or break down under heavy wear or hot conditions. Those of you who are “of a certain age” will remember the term “viscosity break down” from those TV ads. What that means is, conventional oil, at the end of its useful life in your engine, can get thicker when cold, thinner when hot, and will not protect your engine as well as it did when it was new.
Synthetic oil does not suffer that “viscosity break down” as much as conventional oil does, and so it’s less likely that your engine will ever go unlubricated or develop sludge. Have you ever had trouble shifting your bike when you know it’s due for an oil change? You’re feeling that viscosity breakdown, my friend.
I'm Gonna Skip That Next Oil Change!
But hey, that means you can leave synthetic oil in your engine way longer between oil changes right? NOPE. Whether you run conventional or synthetic oil, even the best air filter in the world can’t keep everything out of your motor, and combustion by-products are going to happen. Since your motor has to breathe and has to make a bunch of little explosions in order to work (suck, squeeze, bang, blow!), there’s no avoiding contaminating your oil. Those combustion by-products are not good lubricants, and neither is the fine particulate your bike will inevitably breathe in through its air filter. So, YES, you definitely need to change your oil, and more often when you ride in dusty conditions.
OK, What's The Best Oil?
So what’s the best oil for your motorcycle? The one it asks for. Those dudes you go dirt riding with, and those randos on the internet forums you frequent, are not API scientists and they’re not smarter than the people who designed your motorcycle. They might not be quite as cheap as the lawyers your motorcycle manufacturer has on their payroll, but your motorcycle manufacturer definitely has your bike’s good health in mind when it makes motor oil recommendations.
Do I Need To Keep It Brand-Specific?
Do you need to follow the recommendations for a specific brand of motor oil? No, definitely not. But you do need to follow viscosity and rating recommendations. If your bike specifies synthetic motor oil, you should follow those guidelines, especially if your bike is still under warranty. Conventional oil in a bike that calls for synthetic can and will void that warranty. Saving money by putting cheap conventional motor oil in an engine that specifies synthetic is playing with fire. It might be fine; it might not. Do you want to take that gamble, just to save $10 every 5,000 miles?
So Synthetic Oil Is Always Better, Right?
If your bike does not specify synthetic motor oil, does it help to put synthetic in? Eeeeeh, maybe? This question borders on religion. If you are going on a long trip and you think you won’t be able to change your oil before you get back, and your transmission gets balky when your bike needs an oil change, sure. But you’re most likely wasting money.
What About Mixing Them?
Can you mix motor oils? Yes. Motor oil is motor oil, and you won’t cause any problems if you mix brands, or viscosities (to a point), or synthetic and conventional. Some folks (I’m looking at you, oilhead owners) will put 10W40 in their bike for the cold weather and 20W50 for the summer months, and it’s all good.
Just Change Your Oil.
The best way to protect your engine is to swap out the oil in your engine regularly and on schedule. New oil is better than old oil. The viscosity ratings and API (American Petroleum Institute) JASO (Japanese Automotive Standards Organization) ratings matter, and if your bike has a wet clutch do not use motor oil meant for cars that says “energy conserving” in that API donut. Look in your motorcycle owner’s manual for the oil your bike specifies, use that, and then go ride!