10th Anniversary of the Good Garage Scheme
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Understand Your Car

The importance of oil


 

 

Oil keeps everything lubricated, cool and clean — which is why it gets dirty.

When you start your car, oil begins lubricating your engine. Numerous additives within the oil help it cool and reduce friction between internal moving parts. Oil also cleans away dirt and contaminants, preventing premature engine wear.

For example, for every gallon of fuel that is consumed, about one gallon of water is generated. Most of this water turns to steam and exits through the exhaust (which you may notice on cold mornings when that water actually drips from the tailpipe). But some of this moisture does get into the dead air space of your engine. There, it mixes with other chemicals and forms sulphuric and nitric acid. Dirt and residual fuel will also find their way into this dead air space. The oil must continually keep this area clean so it sweeps away the dirt and absorbs the acids and fuel.

As a result of all the dirt and contaminants it picks up, oil needs to be changed regularly. Also, when oil becomes too old and dirty, you're no longer getting the full benefit of the additives it contains. The oil becomes less effective at cooling and lubricating your engine. What's worse, the increased friction and chemical build-up in used oil can deteriorate your engine's moving parts.


Oil Grades


 

 

You see those cryptic combinations of letters and numbers on oil containers everywhere. So what do they mean?


To indicate viscosity,
The SAE (Society of Automotive Engineers) developed a standard scale.

("W" stands for winter)
0W is thinnest
5W
10W
15W
20W
25W
20
30
40
50
60 is thickest.


To decipher them, you have to understand viscosity.

Viscosity measures the oil's ability to flow. In other words, if you tip an oil bottle over, how fast it spills out indicates its viscosity.

The more viscous it is, the slower it moves.


This means the viscosity is at 10W when the engine is cold and 30 when the engine is hot.

Low viscosities are good for cold temperatures (hence the "W" association!) because the oil is thinner. Thinner oil flows more easily and moves quickly. When you start a cold engine up again, oil needs to travel to the top of the engine, where it trickles back down. Since oil is vital to lubricating your engine, it needs to move quickly and low viscosity helps it do just that.

But when your engine heats up, higher viscosities mean the oil won't thin out too much and will keep parts separated by a film of oil.

So your oil is always maintaining a delicate balance: it needs to flow well when the engine is cold but also retain enough body at higher temperatures to keep metal parts lubricated and separated. To find out what oil grade is right for your car, check your owner's manual.


Octane Explained


 

 

You see the word every time you visit the fuel station but what does it mean?

Octane ratings are a measure of the fuel's ability to resist engine knock. Engine knock is caused by fuel being ignited by something other than the spark plug.

If you are using an octane grade that is too low for your car, something other than the spark plug can ignite the fuel in the engine. The engine could even get hot enough where the fuel explodes by itself.

What octane does your car need?
Check your owner's manual. Don't upgrade to more expensive octane ratings unless your manufacturer recommends it.


On-board Computers


 

 

Most cars today use an on-board computer to monitor and manage several of your car's operating systems. These on-board computers have more memory capacity than the first space craft that went to the moon.

If this computer detects irregularities in your car's operating systems, it will often turn on a dashboard warning light. Using a specialised scanner, a technician can read a trouble code off the computer that details what went wrong.

After 1996, most trouble codes were standardised across manufacturers. So now all cars use five character codes to report problems. The computer can even remember intermittent problems that have returned to normal.

Dashboard warning lights come on if something substantial has occurred. Less serious problems are still detected and stored for analysis by a technician. Early detection of these problems can reduce repair costs and prevent breakdowns.