Engine Oil Lubricants - Basics
Lubricants Basic Info Re: Petrol & Diesel Engines (4 Stroke)

in a past life 25 years ago, I was a sales rep' and Engine & Industrial Lubricants was a large part of my portfolio of which I attended an intensive technical training course at Esso Exxon in Oxford. If I recall correctly, here's a brief synopsis of engine oils which you may find useful.

There are a few quality standards such as 'Society Automotive Engineers' SAE, American Petroleum Institute' API and 'U.S. Military' Mil etc of which they set and test quality standards and viscosity ratings etc. Engine manufacturers upon developing engine technology will liaise with the oil labs and issue their own oil specs for their own engines and to market branded product for a big mark-up.

For petrol & diesel engines, the trend is for multigrades (All seasons use) rather than monogrades (Hot or Cold climates). This is where viscosity comes into play for example 15W/40 or monogrades of 30. With the multigrades the 15W relates to its performance characteristics as a 15 Winter grade from cold start up and as a 40 grade at normal engine operating temperature. Essentially you want a fast flowing oil from a cold start to ensure the oil is pumped quickly around the engine coating all the touching moving surfaces. However, you require a certain degree of viscosity to maintain oil pressure. The viscosity is measured in the lab by the flow rate of a measured amount of oil through a tube at ambient temperature.

Bike Specific oils should always be used with the exception of bikes with a separate gear box (I think the term 'Pre-Unit' is used?). This is because the majority of modern bikes have the transmission gearbox and wet clutch within a common crankcase – like the old Austin Mini. 

Besides acting as a lubricant, oil is actually the main way the engine dissipates heat radiating through the engine structure into the air and coolant. 

Oils were typically mineral based in general and then synthetics became common around the 80s when gasoline turbo engines started to arrive on the scene with the SAAB Turbos, Audi Quattros & Ford Cosworths. These engines ran extremely hot and maintaining oil pressure was a problem that created reliability issues. This required high quality oils usually full synthetics rather than part-synthetic base oils. These are expensive to produce as only a small amount of synthetic material can be extracted from the base crude during cracking/refining compared to what's available for regular mineral base materials. Its not unusual to see a viscosity of 0/30 or 0/60 for certain high performance engines. The '0' doesn't actually mean nil its just the oils measured flow rate. 

Oil cunsumption may be higher in older designed engines due to machining tolerances whereupon modern technology by robotic milling and grinding can produce a 'blue printed' engine repeatedly to exact tollerances. So oil consumption may be less compared to old and the engines tend to be mechanically quiter too.

There can be a little confusion as to what 'Semi-Synthetic' actually consists off and a lot of blends will state 'Semi' giving the impression of 50% synthetic and 50% mineral base blend. I was advised this is rarely the case and the synthetic base may be significantly less.

Very often the 'API' spec is used. Oils for Spark Ignited Gasoline engines are designated as 'S' and Compression Ignited Diesel engines with 'C' and each will have an additional suffix which relates to the year that particular standard was introduced. These letters are combined the general oil spec label. 

Additives/Agents are added into the oils for various reasons such as 'Anti-Foaming', Detergents, Suspension (of particles), Emulsification, Oil Pressure and for special types of engine bearing materials and bore coatings etc. These additives have properties to help lube and cool different parts of the engine for example the cylinder bores and pistons (high heat and scuffing), shell and needle bearings (high speed reciprocal forces) and transmission (heavy mechanical loads) etc.

It is important to consider the viscosity when choosing the right oil for an engine and the manufacturers nearly always suggest a multigrades for temperate climates. The Suzuki air-cooled singles generally 10W/40 SF (or higher suffix than F).

Also, keep in mind bikes tend to have a low volume of oil in total, usually high engine speeds compared cars and trucks so that little amount of oil takes quite a beating. However, keep in mind modern synthetics can considerably extend oil changes compared to a mineral base oil. It was quite revealing that there are only a few lubricant refiners packaging and branding for all the manufacturers so often generic brands of the same spec comes off the same production line as the big brand named oil. So it always pays to shop about.

I have tended to use 10W/40 Part or Full Synthetics for all my bikes over the last 20 years. I tend to change the oil and filters at 6K/KMS for water-cooled and 4K/KMS air-cooled and as per manufacturer when within warranty period.


If non bike specific oil is used it may also have additional additives and be suitable for both petrol and diesel engines. These are generally fine but, check the 'S' spec. The oil companies tech departments can be useful for advice. Also, you can often avail of 'Oil Sampling' of used oil to determine the state of the engine. They can actually define contaminants in the oil such as the type of metal particles which can indicate bearing and coatings wear. This is generally only used for extended drain truck and industrial engines though. 

I'd suggest to buy a full synthetic oil if you intend to travel to hot climates and will be thrashing your poor wee bike loaded like a donkey up Pyrenees mountain passes and over the dunes.

Topping Up – it obviously is best to use the same type of oil however, if you don't have that available try to obtain a similar spec from another manufacturer. And, if you can't obtain either in an emergency I'd suggest you top up with any reasonable engine oil – don't run the engine short of oil, you can always do a fresh refill when possible.

Well, I think that's about right or maybe not. I wonder has anyone even read this far without falling asleep?

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