Difference Between Monograde & Multigrade
What is Monograde Oil?
Monograde is an oil which is only suitable for use within a very narrow temperature range, SAE monograde oils usually fall into 2 main categories:
a) The grades with a ‘W’ after them (SAE 5W, 10W, 15W and 20w) are only suitable for use in the wintertime because they are generally thin oils which are good for use in winter or for cold starting.
b) The ‘Summertime’ grades (SAE 20, 30, 40 and 50) are more suited for warmer or summertime temperatures or for use in an already hot engine.
The problem with monograde oils is that they can only operate efficiently over a narrow temperature range. For example, an SAE 10W oil is fairly thin, which is good for cold starting but it becomes too thin for effective lubrication as the temperatures rise, the oil gets hotter, It starts to lose Its viscosity or thickness. An SAE 40 oil is fairly thick, which provides good lubrication when the engine is hot, but thick oils can cause drag when used from cold (e.g.starting the motorcycle first thing in the morning).
Gear and gearbox oils, which are used in engines where the gearbox is separate from the engine, is monograde oils but they use a different range of SAE grades to measure their viscosity.
What is Multigrade Oil?
Multigrade oil is an oil that has special polymer additives called viscosity index improvers (VIIs). VIIs are added to the oil to help bring the difference in viscosities for most monograde oil that is too large between the extremes of temperature, closer together. These additives also allow the oil to flow easily under cold and hot conditions. Multigrade oil is designated with two numbers:- The first one is followed by the letter “W”. This first number indicates the viscosity (weight) of the oil in winter (cold)
- The second number indicates the viscosity (weight) of the oil under normal engine temperature (hot). It is important for the oil to be thin enough to flow easily when cold. This protects the engine parts from undue wear in cold starting conditions.
Advantages of Multigrade Oils
- One oil for year-round use
- Improved low-temperature starting
- Excellent high-temperature performance
- Improved overall fuel economy – less idling time and faster warm-up
- Less battery drain on cold starts
- Faster, full-pressure lubrication over a wider temperature range
