Engine Oil: What You Need To Know

Just what the hell do those numbers mean anyway?

Oil changes are a staple task for the home mechanic. They're one of the easiest (and messiest) bits of preventative maintenance you can do. If you drive off-road, have a heavy right boot and tow with your vehicle (which probably accounts for 90% of Aussie drivers) you're actually placing your vehicle's mechanical bits under a high amount of strain, so keeping on top of the fluid and filter changes become more and more important the more fun you have behind the wheel.

Insurance doesn't come much cheaper than some new oil and a fresh filter so it's worth knowing a bit about it we reckon.


On that note, just what the hell do those numbers on the side of the oil bottle mean anyway?

Let's say you're staring at a bottle of 10W30 Nulon.

Basically, the higher the number, the thicker the oil is. So the 10W is fairly thin when it's measured at a winter (that's what the W stands for by the way) temperature, or when your engine is cold, the oil will be fairly thin and easily pumped through the tight tolerances found internally in heads and bearings.

As things warm up so too does your oil thicken up to the 30 number. This one is a measure of viscosity as rated by the Society of Automotive Engineers (SAE) and is taken at 100'C (roughly the average operating temp of a normal vehicle).

The gist is that the oil is thin when it's cold so it can flow through the engine and lubricate the mechanical components then thickens once it's warm to prolong engine life. Clever, eh?


Even with a steady supply of fresh oil, your engine will still ultimately wear, which can increase damage to your engine. External contaminants can also build up on inner walls and galleries (which is why diesel oil has extra detergents added). To stop these things from wreaking havoc, your oil filter prevents them from being pumped around the engine. You see where the is leading right?

The longer the engine is running, particularly under load such as when towing or driving off-road, the more contaminants the filter has to catch and the dirtier and less effective it becomes.

So yeah, 25,000km services are all well and good for a road-driven-only vehicle that never sees heavy loads or off-road duties. But for the majority of us, aim for 5,000-10,000km service intervals with a fresh filter. Again, insurance doesn't come any cheaper.


You know how some oils say they're synthetic, and generally cost more than double the equivalent mineral-based oil? That's because synthetic oils really do have a lot more to offer and are worth the higher asking price if you want the best for your engine.

In a nutshell, they function better at extreme temperatures and do not lose out on lubrication qualities when towing your 25ft plate boat up that sand dune in the middle of summer.

Synthetic oils also generally last longer, suspending contaminants in the fluid more efficiently, so while filter and fluid changes are still a must, it's way less strain on your engine in between services. The sticker shock is simply the price of getting out and having fun in your vehicle. Sucks, but it's still totally worth it.


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