Monograde and Multigrade are mineral based oils which have different characteristics.Measuring the oils ability to flow is called viscosity, which is a test carried out under normal working temperatures.

Monograde is thicker when cold, so to be able to use oils when in cold conditions a modern Multigrade oil is available. This has the ability to be thinner under cold climates and gets thicker as it heats up.

As the oil gets tired, it turns black from the contamination of small carbon particles from exhaust leakage which passes through the piston rings. These carbon deposits need to removed from the oil as they are abrasive and will damage the engine, this is achieved via;

• Filters : consist of regularly replaceable cartridges which the oil passes through from the engine to the oil reservoir/tank. The filter then traps the carbon deposits and leaves the oil clean to lubricate the engines vital moving parts.
• Sludge Traps : centrifuge consisting of a drilled hole in the crank web on the flywheel. As oil passes through the trap, the carbon deposits, which are heavier, are thrown into the trap by the centrifugal force created by the spinning crankshaft. The sludge which has been left in the trap will need to be cleaned out on a regular basis, which, will require the engine to be stripped completely.

Which Oil ?

If the motorcycle you own is has a sludge trap, Monograde is ok, it will require regular changing as it doesn't consist of the additives required to move the carbon deposits.

If the motorcycle you own has a filter fitted, Multigrade should be used. This oil which passes through the filter has the ability to last longer between the oil changes. It has the additives, detergents and dispersants, which carry the carbon deposits through the filter and prevent it settling in the engine. This will result in a cleaner engine when it is stripped down.

As with any further developments, oil has been made better over the years, if you want to protect your classic motorcycle, fit a filter and use Multigrade oil.