Thursday, 16 July 2015 00:00

Never Too Safe

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The Good Oil on the Good Oil - A liquid tune up

Now I bet most of you would not associate giving the car an oil change with making it go faster – but it does, so let’s explain why.

When the engine is running, no moving parts actually touch any other, instead they are held apart by a very thin layer of oil. How thin you ask? Well let’s take the crankshaft as an example. Once the oil light goes out, the crank is actually floating on a layer of oil of somewhere between .01 and .03 millimetres thick. To give you an idea of how thick that is – the hair on your head is around .075 millimetres. So we are talking teensy, weensy clearances here.

Now this layer of oil we are talking about is also between the piston rings and the cylinder bore. Matter of fact, without this oil layer the engine probably wouldn’t start, because not only does the film stop the rings tearing themselves and the bore apart, it also seals the combustion gases in.

Engines with low compression are hard to start and have low power outputs because a lot of the pressure developed in the cylinder due to the burning fuel heating and expanding the air, leaks past the rings and into the sump.

Why this occurs is due to the dilution of the oil by water and petrol. The water is a natural by-product of the combustion process (you most likely have seen it running out the exhaust when the car is cold), and when the car is hot, it just vaporises during the combustion process. But when the car is cold, it condenses on the relatively cool parts of the head and cylinder walls and runs down past the rings into the sump. Same happens with the petrol. Not all of it is burnt when the engine is first started and because the oil is also not up to temperature and doing its job, some of the fuel ends up in the sump.

So over a period of time, your oil gets diluted and thinner. It then does not seal the cylinders as well and you lose power. Not to mention the extra wear that takes place on the engine.

So how often should it be changed? Well that depends on how you drive it. Your owner’s manual may suggest up to 15,000k between oil changes. If you are operating under extreme service conditions, those figures should be halved at least.

What’s extreme service?

  • Long periods of idling, such as in traffic.
  • Short runs where the engine does not get hot
  • High speed driving e.g. track based events
  • Towing heavy loads

The sort of things we do with our cars all the time. However the good news is that if you live in Melbourne and work in Perth, the long drives to work where the car is hot and running under reasonable load all the time will mean that 15,000k oil changes will be fine!

As stated if you are taking the car to the track this qualifies as an extreme service condition. You should aim to check and be prepared to change oil every 5,000kms. Check levels a day or two before you go to the track and at the end of the track day. It is always advisable to take a can of oil with you to the track. A 5 litre container of oil could save you $$$$.

OK, now we know that the manufacturers are telling us a bit of a porky, what’s a good distance? For normal driving 5000k is fine and only change the oil filter every second change because the oil won’t be as dirty in the first place, so the filter won’t have as much junk in it.

Which oil?

That's for our next article...come back soon.

Read 22301 times Last modified on Monday, 24 August 2015 09:59

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