All About Oil


My wife has a saying she uses to remind me to drink more water. “Water is like oil for your body,” she says. She knows which analogies work for a guy. I’m going to turn that around and say that oil is like the source of life for your engine. Using the best possible oil and changing it regularly is probably the single-most important thing you can do to maintain the life of your vehicle. Most of you probably already know this. Some people don’t. I once overheard a conversation at my garage with a woman who didn’t know she had to put oil in her car or where to put it. She’d let the car run dry and the engine had seized. But not to pick on women, I know a guy who did the same. “Ah, dude. Here’s your problem. There’s no oil in this car.”

Given the importance of oil, it’s surprising there are so many misconceptions about it. I fell to one recently by putting the wrong grade in my bike, based on a recommendation from the previous owner. He said, “You have to put 20W-50 in a motorcycle because it revs high.” So I did. Then I had trouble starting my bike once we got into the cold mornings of late fall and early spring. I started to suspect my cold-starting problems were related to oil, and a user forum referred me to I don’t know who Bob is, but he knows a lot about oil. You will find at this site Motor Oil University containing ten classes complete with midterm and final exams. Clearly, oil is the source of Bob’s life.

The following is, I hope, a fair summary of what I’ve learnt mostly at that site, but also from user forums and conversations with club members as I researched the important decision of what to put in my bike. This should be useful for car owners as well as bikers.

Let’s start with some of those misconceptions:

  • Engine wear occurs when oil breaks down at high temperature
  • Oil grades like 10W-30 or 20W-50 refer to viscosity, or thickness
  • You should choose your oil grade based on the ambient temperature
  • Engines that run hot, like sports cars and hot-rods that have high revs, require thicker oil (this is the one I fell for)
  • You should change your oil when it turns black


Engine wear occurs when the engine gets too hot

Actually, 90% of engine wear occurs at start-up. And sadly, there is no oil on Earth that fully protects an engine at start-up; a good quality oil can only minimize the damage. This is why it’s important never to rev your engine when you first start it, especially in the wintertime. My ex-wife used to get out of bed 10 minutes before her train left the station, then, in -40 Celcius Montreal mid-winter, would race the three blocks to the station immediately upon starting our car instead of walking. Don’t do this. No wonder she’s my ex.

To minimize the damage, you want your oil to be as thin as possible upon starting. So why not just buy the thinnest oil, you ask? Because there are actually two temperatures we have to be concerned about. One is starting temperature, and the other is operational temperature.

The two numbers on the oil container roughly correspond to these two contexts. But that’s about as direct a connection as you should draw, and many people (including Bob) suggest you forget about the numbers and labels for a few reasons. The W in 10W-30, for example—a reference to winter—is a misnomer. It would be more accurate to think of the first number in relation to starting temperature. Moreover, the numbers do not really reflect viscosity because viscosity changes with temperature. For example, according to Bob, a straight 30 oil has a thickness of 250 cS (centiStokes) at 75 F, but 10, the ideal viscosity, at 212 F, the optimal operational temparature.

The second number refers to operational temperature, but all liquid-cooled engines (i.e. most bikes and all cars) have a constant operational temperature of 212 F. Ambient temperature while running is only a consideration if your bike is air-cooled, like many BMWs (but not mine) that have the distinctive look of the cylinder heads jutting out sideways into the onrushing air.

Confused? You’re not alone. Now let’s add another factor.

Mineral vs. Synthetic

There are few more controversial issues amongst bikers than which is better, mineral (i.e. regular) oil or synthetic. The debate in Hell between the fallen angels in Book II of Paradise Lost has nothing on the debates in user forums on this topic. If you want to have some fun, go to a popular forum (I won’t say which out of fear of being banned) and pretend to be a newbie, asking innocently which you should use. It’s like throwing a french fry to a flock of seagulls at a tourist rest stop.

Many people believe the biggest difference between mineral and synthetic oils is that mineral is natural and synthetic is made in a lab. That’s a pretty big difference, for sure, but the more significant one for your engine is that synthetic is “naturally” thinner at start-up, the crucial time when most wear occurs. That is, it does not thicken as much upon cooling as mineral oil. The viscosity of the two are identical at operational temperature but synthetic has the edge on start-up. One point for synthetic.

Another difference is that, for example, a synthetic 10W-30 oil is based on a 30 grade oil and a mineral 10W-30 oil is based on a 10 grade oil. The mineral oil has additives in it that prevent it from thinning excessively as it heats up, and it’s these additives, not the oil itself, that break down over time. So with age, a mineral oil will lose its viscosity. This is why you have to change a mineral oil sooner, about twice as often, as synthetic oil. Second point scored to synthetic.

These additives age even outside of use in extreme temperature. Don’t store your mineral oil in the shed during winter because it will lose some of its viscosity. In fact, contrary to what you might think based on what I’ve said above, Bob says that mineral oil ends up too thick, not too thin, with age. I don’t know why, and now I’m as thoroughly confused as you must be, but thankfully Bob offers this summary, twice, because it bears repeating:

“The synthetic 10W-30 grade oil is based on a heavier 30 grade oil while the mineral based 10W-30 oil is based on a thinner 10 grade oil. They are both similar at operating temperatures yet the 30 grade based synthetic is actually less thick at startup and much less honey–like at low temperatures. This is the opposite of what common sense dictates.”

It would seem that synthetic, in the red corner, is the winner, but wait: my BMW owner’s manual says “Alert: Do not use synthetic oil.”

Ah, there’s the rub

I’ve never seen any rationale for this, not at least from BMW, but there’s some anecdotal evidence on user forums that synthetic oil can produce clutch slippage. Remember your dad yelling at you “Don’t ride the clutch!” when you were learning how to drive manual? That’s because cars have a dry clutch. But all bikes today have a wet clutch, meaning it’s lubricated by oil, the same oil that’s lubricating your engine, so you can ride it all you like, and should, because there are lots of times when you’re between gears.

But because synthetic oil lubricates so well, it can lead to the clutch slipping. Because I’m a Gemini and familiar with the squabbling twins, I like compromise, so ended up putting semi-synthetic in my bike. I only ever experience clutch slippage when I’m really givin’ ‘er, like accelerating on a highway on-ramp, and notice the tac jump but don’t feel the corresponding pull of acceleration. The upshot is that gearing is much smoother, the engine quieter, and (so I presume) the engine less worn. This summer I’m going to adjust my clutch and hopefully that slippage will disappear.

High-Rev engines need thick oil

When I was 18 I worked as a self-serve gas attendant at Sunoco. We had cans of oil stacked on the shelves inside the kiosk and the tattoo boys would pick up 20W-50 for their muscle cars. Now at 53 (next week), I can laugh at them for wrecking their prized possessions. Bob says you don’t need that oil unless you are going to the track, not the bar or corner store (or gas station, for that matter). He says that for all he knows about oil, even in a hot engine, it’s better to go thin than thick. Why?

As I’ve said, normal operating temperature is 212 F. At that temperature, most engines want the viscosity at 10 cS. The thick multi-grades have a viscosity of 20 cS at that temperature. Not perfect. But as Bob points out, when we increase the temperature from 212 F to 302 F, the 10W-30 thins from 10 cS to 3, but the thicker oil thins from 20 cS to 4, only 1 cS different. So the difference in viscosity in a hot engine is negligible while the difference at start-up is huge. If you need any more proof that a thicker oil isn’t worth the cost at start-up, Bob says that F1 cars run a straight 5 or 10 grade oil.

Change your oil when it’s black

No, change your oil when you’ve driven the recommended distance for the oil or when the recommended time has elapsed. (Remember, oil ages even when it sits, so even Grandma has to change it regularly.) There are a number of factors that can turn an oil dark, but that doesn’t mean it’s lubricating less. Don’t believe me? See this page on motor oil myths by Valvoline. You’d think an oil company would want you to change it prematurely, but they say otherwise.

The final answer

What did I put in my bike? I put a semi-synthetic Ester-based 10W-40. This vid by Ari at MC Garage says not all synthetic oils are created equal and to look for one that’s Ester-based. I read that back in the 70’s, Mobil took Castrol to court for advertising its Syntec oil as synthetic. It’s all about the base that’s used. In the end, the court decided that Castrol changed its oil enough to call it synthetic, but if you’re looking to put a top-quality synthetic oil in your car or bike, look for one that has a base of PAO (Poly-alpha-olefin) or “esters” (chemical compounds consisting of acarbonyl adjacent to an ether linkage. Are you listening, my Chemistry colleagues?).

The other goof I made was forgetting to check the oil level at operational temperature. This is contrary to a car, which you check after it has been turned off for at least 30 seconds. When I took the bike out of storage this spring, I checked the level at start-up and, not surprisingly now, it was low, so I added a good litre. Doh! BMW’s have a sump pump system and it’s essential to check oil after at least twenty minutes of riding, with the bike level, pointed North, at a full moon . . .

Fortunately I caught that one before I caused serious damage to the engine. (Overfilling can cause seals to melt, among other problems.) Now I have the oil in it that I want, and at the correct level, which apparently is on the Min. line. I hear from both The Chain Gang and my BMW guy that these bikes don’t burn oil, and it’s better to err on the side of low than high. I think I’m set now for the season, including the fall. That’s good because an oil change on my bike is a full day affair. I’m envious of Pirsig who writes of changing the oil practically while Chris takes a whiz, while on my bike I have to remove half the fairing, the crash guard, engine guard, etc.. But what I pay in labour and cost for synthetic I gain in peace of mind, knowing I’ve got the best stuff known or made by man in the crankcase.

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