How oil works

How oil works

It is the stuff that keeps our cars alive and our motors singing their wonderful songs of horsepower and joy... but what do you actually know about the magical liquid keeping everything spinning nicely? Oil is a simple three-letter word that actually encompases a world of different products, but the basic premise for most cars is oils lubricate rotating parts. 

But there is a world of science behind engine oil (and, like our friends at Castrol say; "oils ain't oils"), so lets dive in and work out what is the right oil for your car. To begin with, every car manufacturer recommends a particular oil for a car, going right back to the '50s, and you can either find this information in your handbook or through a bit of Googling.

You'll hear a lot about "full-synthetic", "semi-synthetic" and "mineral" oils and this can be confusing. Which is better, why use one over the other, and why does MOOG cook his eggs in baby oil? 

Mineral oil is the simplest to answer: it is essentially just refined crude oil made out of crushed dinosaurs and dug out of the ground. It typically has been the cheapest oil to buy, as it doesn't include all the additives used in synthetic and semi-synthetic oils.

Synthetic oil is lab-developed to include additives to assist coating technology, improve viscosity, or add in detergents to help clean the engine internally, among many other potential addiitives. Modern high-performance engines run far tighter tolerances and perform under higher stress levels than old school engines, and this mandates the use of full synthetic oils.

Semi-synthetic is a blend of mineral and synthetic. These oils are often now the cheapest to buy in a retail setting.


When starting a brand new engine many builders will recommend a mineral oil to help bed the piston rings in. Without the detergents and additives used in synthetic oils the mineral oil is a better choice to make the stressful job of bringing a new engine to life simpler.

Many old engines, particularly ones with flat tappet camshafts, work best with a mineral oil that has a high zinc content, as zinc assists with metallurgical wear inside the engine. Modern engines with improved casting processes, metals used, and technologies (like hydraulic roller cams) mean that zinc isn't crucial, which means it can be difficult to find high-zinc oils today.

The numbers on the bottles, like 5W-30, 20W-50, or 0W-60, relate to the viscosity of the oil, or the slipperiness of the liquid. The lower the number means the oil flows faster when the engine is cold, while the higher number relates to the oils viscosity at the engine's operating temperature.

As different engines run at different temperatures, they will need different oil specs. Some car owners live in parts of the world where weather conditions mean the engines need to change oil specs to keep up with the change in extreme swings between seasons. Sometimes mechanics will also recommend running a thicker oil in a very high-mileage engine, or one which is considered tired (maybe a little smokey or rattly). 

Similarly, if you get your engine built and the tolerances of the engine are changed (eg: relaxed, or tightened up) to suit the new set-up, then you might very well need different specification oil. 

Standard most LS engines run full synthetic 5W-30, but Troy Worsley from Warspeed Industriews who built by supercharged, forged 403ci stroker (below) recommends a specific mineral 10W-60 for high-compression, forced-induction LS engines... and this is different from the oil he recommends for the 2Js he's built, or his 10,000rpm 1500cc Toyota 5K.

Engine oil is recommended to be changed at least every 10,000km but most mechanics will recommend 5,000km or 6-month intervals. The more short trips and stop-start driving you do, the shorter your oil change intervals need to be. 

If you've started pulling more power out of your engine, you really should run on a 5000km service interval, including changing the filter with a quality replacement. And, if your car has an aftermarket oil cooler, remember you'll need a little more oil to fill that (it may also require you to drop a line off to drain it). 

Check the oil weekly when the engine is cold and the car is parked on a properly flat, level surface. This ensures you'll get an accurate reading, as the reading will be low if you have started the car as oil has to run to the top of the engine to lubricate the valvetrain. 

All up, if you have questions about what oil you should use, when you should change it, and why, the best idea is to ask a trusted engine builder who has experience with your type of car (or engine).

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