Understanding ATV Oil Viscosity Ratings

Oil is the blood that keeps an ATV engine pumping. It creates a film to lubricate and separate the parts and reduce wear. It also removes heat from an engine. OK, so you know an engine needs oil in order to function, but what do the numbers and letter on a container of oil mean?

Viscosity is the measure of how easily oil flows at a given temperature. The Society of Automotive Engineers (SAE) determines oil viscosity through regimented test procedures. Thin oils (lightweight) have a low viscosity rating, thicker oils (heavyweight) have a higher viscosity rating. Most oils today have two ratings — the first number is a rating at low temperatures and the other is its rating at warmer temperatures. These are called multi-viscosity lubricants.

The letter “W” on a bottle of 5W-30 stands for “Winter.” It has a viscosity rating of 5 at 0 degrees F, which is relatively thin so it will flow easily when cold. The second number refers to the oil’s thickness at warmer temperatures — the lower the viscosity, the thinner the oil. Oil rated 10W-30 will be a little thicker at startup, but once the engine reaches normal operating temperature, its characteristics will be the same as the 5W-30 lube. A 20W-50 oil, for example, is common in some high-performance ATV engines because its thicker viscosity won’t break down in high-heat applications like racing. If you use your quad in a cold climate, this might be too thick, especially at startup.

Most oil viscosity ratings are between 0 and 50. An oil that’s too thin won’t provide adequate protection if the engine is run hard or used in hot weather. Oil that’s too thick might not allow the engine to turn over in extremely cold weather, nor would it flow well enough to provide adequate protection of the piston, cylinder, valves, camshaft, rocker arms and related engine parts when the engine is cold.

Yamaha's new YZ engine design, will the YFZ benefit?

Regular readers of my articles know I am not an engineer, nor some fancy pants engine builder, I don’t claim to be either.  What I am is a motorcycle enthusiast with a side of ATV interest. (read my bio HERE )  So when the motorcycle side of the industry introduces a interesting new concept to mass production, my eyebrows raise and my mind thinks “Will this translate to ATV technology and design?”

Inside the new YZ450F engine

Yamaha has pretty much shocked the motocross world with a complete redesign of their YZ450F motocross bike, especially in the engine department.  In a nutshell Yamaha has turned the engine (specifically the top end) back wards putting the intake in the front and the exhaust in the rear.  The cylinder is also offset from the crankshaft to maximize the transmission of the downward force on the compression stroke.  When you think about it, that is how it should have always been   Mass centralization is the name of the game as well as more power from the better flow characteristics.  Now this concept is not entirely new, Yamaha used this type of layout on their 2 stroke GP bikes in the 80′s.  Of course Cannodale used a similar layout as well as Huesaburg has their intake in the front although their engine is even more radical as it uses a stacked transmission (much like a sport bike).  Usually these types of radical departure from the norm either succeed or fade into obsucrity (a-la the CRF250 with its dual exhaust).

Why go into all this when the development is not even on an ATV?  Well much like my last blog entry, I want to ask the question,  When (and if) we will see this technology be translated over to the ATV world?  My personal opinion is “yes” but probably not for a few years.  However in saying that, why is it that sport ATVs generally lag behind in the performance development?  The only notable exception is with the LTZ450 having EFI before the motocross bike, but even that is a moot point as Gas Gas pioneered EFI on a dirt bike and ATV back in the early 2000′s. I am interested in your thoughts on the subject.  Leave a comment or discuss it on our own ATV Forum.

Engine configuration explained