Oil
How to choose engine oil for your car/bike
How to choose an oil for your car or motorcycle is a subject that is very close to the heart of many enthusiasts. I do not intend to go too deeply into the subject here as there is loads if information on the web for all to see.
Engine oil has changed over the years at a fantastic rate, Many people think that as they have an old design of engine any old oil will do, but at the end of the day, the oil stops metal parts grinding together whether the engine is old or new. There are three main classes of oil, mineral (the oldest), semi synthetic and fully synthetic. When only mineral oil was available, additive packages were combined with the oil in production, this meant that oil change intervals were driven by the life of these additives, when they started breaking down, the oil needs changing. There were bottles of additives that could be added to extend the life a little such as Wynns or STP. With the synthetic oils additives were not needed in such great quantities so oil change intervals were extended. Synthetics also allowed the oil manufacturers to fix the viscosities (thickness) better with out additives so that the oils would last much longer.
Viscosity has also changed over the years, a 20W50 mineral oil is not as good at lubricating as a 5W40 synthetic because the latter has longer chain molecules to keep metal parts away from each other. The first figure is the viscosity of the oil when cold, this is very important. It may be a lower number than the second figure but that does not mean that the oil is thinner. Most engine wear happens on start up and a 20W** oil could take 10 times as long to get to parts of the engine than a 5W** would. This means that for a couple of hundred engine revolutions, some parts of the engine will be running without oil.
The second figure is for when the engine is hot. The oil is still thinner than when it was cold despite the number being higher. A **W40 synthetic will lubricate better than a **W50 mineral due to the long chain molecules. If you think of these molecules as hair cuttings on a flat piece of metal with a ball bearing rolling about on it, it is obvious that hair cuttings that are a quarter of an inch long would not keep the ball bearing away from the metal as well as cuttings 2 inches long.
The other advantage to a synthetic is the temperature tolerance. If you heat a mineral oil in a frying pan to around 150C, the additives will break down and you will end up with treacle, and that does not lubricate at all. If you do the same with synthetic, there are very few additives to break down and you will still have oil above 190C. People may think that their engine never gets that hot, but in some parts of the engine it may do.
Motorcycle oils are a little different in that they are designed to also lubricate gearboxes in some bikes and the grinding of gears on an oil requires different properties. Most bikes, apart from BMWs and some others also have wet clutches that run in oil. If you want your clutch not to slip then why run it in oil? BMW bikes will be quite happy with just normal car engine oil.
Synthetic oil is what many HGVs use, this allows them to have 50,000 mile oil change intervals. Many modern diesel cars specify only fully synthetic oil and have change intervals up to 20,000 miles.
So why do BMW specify an oil change every 6000 miles? Well, they know that people will chuck any old oil in their bike, and the dealers need to have something to keep them in business. BMW cars manage 20,000 mile oil changes (on fully synthetic).
Here on the continent, synthetic oil is not the hard to find expensive stuff that you find in the UK. It is on all supermarket shelves for around 20 euro for 5 litres.
In Judes bike we use a 5W40 synthetic and in mine a 5W50. The reason for the difference is that mine has less than 10,000 miles on it and still vibrates through the bars at some speeds, when mine is also run in it will get 5W40 too.
Reprinted w/o permission as originally published @ http://bikesindordogne.blogspot.com/
How to choose an oil for your car or motorcycle is a subject that is very close to the heart of many enthusiasts. I do not intend to go too deeply into the subject here as there is loads if information on the web for all to see.
Engine oil has changed over the years at a fantastic rate, Many people think that as they have an old design of engine any old oil will do, but at the end of the day, the oil stops metal parts grinding together whether the engine is old or new. There are three main classes of oil, mineral (the oldest), semi synthetic and fully synthetic. When only mineral oil was available, additive packages were combined with the oil in production, this meant that oil change intervals were driven by the life of these additives, when they started breaking down, the oil needs changing. There were bottles of additives that could be added to extend the life a little such as Wynns or STP. With the synthetic oils additives were not needed in such great quantities so oil change intervals were extended. Synthetics also allowed the oil manufacturers to fix the viscosities (thickness) better with out additives so that the oils would last much longer.
Viscosity has also changed over the years, a 20W50 mineral oil is not as good at lubricating as a 5W40 synthetic because the latter has longer chain molecules to keep metal parts away from each other. The first figure is the viscosity of the oil when cold, this is very important. It may be a lower number than the second figure but that does not mean that the oil is thinner. Most engine wear happens on start up and a 20W** oil could take 10 times as long to get to parts of the engine than a 5W** would. This means that for a couple of hundred engine revolutions, some parts of the engine will be running without oil.
The second figure is for when the engine is hot. The oil is still thinner than when it was cold despite the number being higher. A **W40 synthetic will lubricate better than a **W50 mineral due to the long chain molecules. If you think of these molecules as hair cuttings on a flat piece of metal with a ball bearing rolling about on it, it is obvious that hair cuttings that are a quarter of an inch long would not keep the ball bearing away from the metal as well as cuttings 2 inches long.
The other advantage to a synthetic is the temperature tolerance. If you heat a mineral oil in a frying pan to around 150C, the additives will break down and you will end up with treacle, and that does not lubricate at all. If you do the same with synthetic, there are very few additives to break down and you will still have oil above 190C. People may think that their engine never gets that hot, but in some parts of the engine it may do.
Motorcycle oils are a little different in that they are designed to also lubricate gearboxes in some bikes and the grinding of gears on an oil requires different properties. Most bikes, apart from BMWs and some others also have wet clutches that run in oil. If you want your clutch not to slip then why run it in oil? BMW bikes will be quite happy with just normal car engine oil.
Synthetic oil is what many HGVs use, this allows them to have 50,000 mile oil change intervals. Many modern diesel cars specify only fully synthetic oil and have change intervals up to 20,000 miles.
So why do BMW specify an oil change every 6000 miles? Well, they know that people will chuck any old oil in their bike, and the dealers need to have something to keep them in business. BMW cars manage 20,000 mile oil changes (on fully synthetic).
Here on the continent, synthetic oil is not the hard to find expensive stuff that you find in the UK. It is on all supermarket shelves for around 20 euro for 5 litres.
In Judes bike we use a 5W40 synthetic and in mine a 5W50. The reason for the difference is that mine has less than 10,000 miles on it and still vibrates through the bars at some speeds, when mine is also run in it will get 5W40 too.
Reprinted w/o permission as originally published @ http://bikesindordogne.blogspot.com/
Labels: maintenance/wrenching
posted by DAbbott @ 8:38 PM
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