I worked for an oil company for 12 years and we manufactured and blended a variety of oils for a number of uses. used world wide.
The majority of specialist oil companies, buy base oil from one of the majors ie Shell, Exxon (Esso),Texaco,Mobil Etc. and then blend to produce the properties they require depending on the application. you will see specialist oil companies such as Silkolene and Rocol, but Castrol is the biggest specialist blender with a wealth of experience and knowledge. Motor oils vary enourmously and with the advent of viscosity index improvers they can range from £1 / litre to £15 /litre ie mobil 1, Castrol Edge. These oils were developed to extend the service intervals of high performance road cars.
the 2 enemies of oil are heat and friction, and obviously both are linked. When engines are operated the oil starts to degrade through polymer chains being sheared, (this is why the old engine oils were thin as water when they were changed.) the second is oxidation through heat, this is what turns your oil black (carbon) also wear particles suspemded in the oil appear black.
All motor oils have to be tested to a British standard this can be found on the oil container. in order to make oil choice easier. In reality it becomes personal preference.
The GX160 engine is not a high performamce engin even in its tuned form.rarely revving above 7,000rpm, It is unlikely that any high performamce oil would break down,however like stated by everyone here they have no means of filtration, and therefore the particle are carried around the engine and it is this that causes the wear. Cool power is a very popular brand well supported by engine tuners. it is low viscosity and performs well in these engines.but equally there are other excellent oils available.
Go with the brand you are happy with, or your engine tuner recommends after all these are the guys that work with the engines and see the wear during rebuilds. most people swear by Cool power and some say it reduces your lap times by 2/10ths /sec.
In conclusion, use whatever oil your engine tuner recommends, normally Cool Power. or a high grade synthetic branded oil (Mobil 1 , Castrol Edge)and change as frequently as you can afford too, after each meeting or every other meeting. if the oil is black change more frequently until you get to a situation like Graeme where the oil is clean when you change it.
Incidently there is an argument that says use a standard 30 grade mineral oil for the 1st few runs to allow the engine to bed in, again speak to the engine supplier on this one.
hope this helps John Martin
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