Harley Davidson Engine Oil Selector

Motorcycle Engine Oil FAQ

Can I use car engine oil in my motorcycle?
This can be risky. Even though you can and will find car oil with the same viscosity ratings (i.e. 10w40) as for motorcycle engines, the additives in the oil will be different. Most cars use a separate gearbox oil and most cars have a dry clutch. So a car oil could make your clutch slip or knacker your gearbox. If you're buying a bike that's been run on car oil, beware!

Does engine oil have an expiry date?
Engine oils have an expiry date which means the performance levels can no longer be guaranteed. However if your oil hasn't been opened, it'll take years and years for it to degrade. If your oil has been opened and is a couple of years out of date, it'll most likely be absolutely fine. However, if you've already opened it and it's 5 years out of date you'll be better off buying fresh oil as the additives in the oil may have oxidised and lost their qualities.

What are the most critical areas where the oil flows?
For a motorcycle engine, the critical engine areas are the piston assembly, bearings and valve train. The engine oill also lubricates the clutch (but not if your motorcycle has a dry clutch) and your motorcycle's gearbox.

What does my oil filter do and do I need to replace it?
The oil filter traps foreign particles and debris that are introduced into the oil by normal riding. These particles can be anything from carbon deposits to small metal particles from your motorcycle's engine. These particles can lead to engine damage, while a blocked filter may lead to oil starvation and ultimately engine failure. An oil filter costs just a few pounds, so it makes sense to change this every time you do an oil change.

What is the difference between a mineral, semi-synthetic, and full-synthetic engine oil?
Mineral oils are refined from petroleum, but even mineral oils contain some synthetic compounds or additives to improve them. Semi-synthetic oils are a blend of mineral and synthetic oils. They have definite improvements over pure mineral oils. Semi-synthetics can contain “hydrocracked” bases. Hydrocracked oils are mineral oils that have been subjected to intense pressure and temperature to change the structure of the molecules, making the resultant oil more stable and resistant to evaporation at higher temperatures. Semi-synthetic oils don’t cost much more than mineral oils do, but offer advantages over the latter.

Why does a 2-stroke oil have to be mixed with fuel?
A 2-stroke engine is built and runs differently to a 4-stroke one. A 4-stroke engine keeps most of its oil in its crankcase and oil sump and recirculates this oil to lubricate the engine. With a 2-stroke engine, the process is somewhat different. Here, there is no oil sump as the crankcase deals with the compression and induction of the fuel/air mix. The only way, therefore, to provide oil to the engine for lubrication is by adding it to the fuel. As this oil is burnt with the fuel, it can’t be recirculated. A specific 2-stroke oil is needed as 4-stroke oil would leave damaging deposits behind when it burns.

Is any engine oil better than no engine oil?
Yes, but when it comes to motorcycles, the 'right' engine oil is better than 'any' engine oil!

Why do some engines burn oil?
Unfortunately, some types of engines just use more oil than others due to their design. Here, the burnt oil can leave damaging deposits behind, meaning these engines often need more top overhauls. However, if a touring engine uses more oil than is necessary, changing to a lighter grade of oil often solves the problem.

Can I top up my engine with a different type of oil?
As long as you don’t mix a 2-stroke oil with a 4-stroke oil, you can safely top your engine up with a different type of oil. You probably wouldn’t want to mix different grades, say, a 5W-30 synthetic with a 20W-50 mineral oil, but if you do, it likely wouldn’t do any harm.

Do I need to warm up my engine before riding?
The oil needs to be warm, but, even better, hot, especially when riding at speed. When cold oil is pumped into an engine, cavitation (bubbles of vacuum within the oil) is likely to occur. This, in essence, means that the engine does not receive enough oil for it to run optimally at speed. Warmer, and so thinner, oil ensures that the engine not only receives enough oil, but that all moving parts within it can work optimally. Ideally, use a 5W-40 or 10W-40 oil and ensure the engine warms up properly for a few km before speeding up.

Do I need to regularly change my oil?
If you tend to drive short distances with a low annual mileage, regular oil changes are vital, irrelevant of whether the minimum mileage for an oil change was reached or not. Water vapour and fuel tend to make their way into the oil, and, unless you drive long distances, they never have the chance to evaporate. This can cause damages like corrosion, gear tooth pitting, and ring and bore wear. Long-distance riders with a high annual mileage who use a high-quality oil can afford to be a little more relaxed on the oil changes.

What's the best type of oil to use in a road bike?
Your ideal choice of oil would be an ester semi-synthetic 10W-40 or a 10W-30 that is also shear-stable. The fact that the oil is shear-stable is more important than the fact that it is semi-synthetic. You are still better off choosing shear-stable mineral-based oil than a low-quality semi-synthetic one that isn’t shear-stable. Only for frequent long-distance riders would the cost of a full-synthetic oil be worth it, as it can help save on oil changes and fuel costs.

How does oil 'cling' onto the engine's internals?
Where there is high-speed rotation in the engine, e.g. with a plain bearing, the high speed draws a thick layer of oil between the two surfaces, like a wedge. Here, this oil supports and carries the load of these surfaces. As soon as the spinning stops, however, either due to the slowing down or stopping of the engine, this wedged oil gives way. Where no rotation occurs in an engine, oil cannot form this thick wedged layer to protect metal surfaces. Here, oil provides a thin protective film and often relies on anti-wear agents, detergents, and anti-oxidant chemicals to help protect from metal-to-metal contact.