Possibly the initial motor oil performance enhancers were actually Motor Oil viscosity index modifiers: Remember STP...? In those times they were simply identified as motor oil additives.

What's a motor oil Viscosity index modifier?

(VI) is a popular technique of calibrating a fluid's change of viscosity with regards to temperature. The greater the VI, the lesser the relative change in viscosity with temperature. VI improvers (also called viscosity modifiers) are additives that improve the viscosity of the fluid all through its useful temperature range.

Viscosity modifiers are polymeric molecules that are sensitive to temperature. At low temperatures, the molecule chain shrinks and does not effect the fluid viscosity. At higher temperatures, the chain unwinds
and an boost in viscosity takes place.

A good analogy is to think about this chain as a slinky, a lazy-spring coil-shaped toy. Operating you might say similar to the people in a hallway. The slinky shrinks when colder and extends out when hot. When shortened, the molecules effortlessly flow past each other, but when expanded, they get trapped on each other and slow down the movement of the fluid they occupy.

You can find two approaches to describe the properties of these types of polymer chains. The very first is to compare the polymers to people. Whenever a person is cold, his normal response is to keep his arms close to his body to maintain heat. Now picture a group of cold people, arms drawn in, moving past each other in a busy passageway. For certain there's some over-crowding however the people can continue to move unhampered.

Now picture the contrary. Whenever a person is hot, he is likely to sprawl out. Imagine a person keeping his arms straight out from his sides. It would certainly be a lot more challenging to get around a busy passageway full of hot people, arms extended. Consider in this example, the movement of people is related to the viscosity of the group.

Bear in mind that as temperature raises, the viscosity reduces. The inclusion of modifiers is only going to decrease the rate at which the viscosity reduces.

Why would a Motor Oil viscosity index modifier be required?

Viscosity index modifiers are mainly used in multigrade engine oils, gear oils, automatic transmission fluids, power steering fluids, greases and different hydraulic fluids. Many of these uses entail a vehicle, and this really is due to the fact cars are exposed to huge temperature shifts.

For example, in the crankcase, an oil with a lower viscosity at low temperature is required so the oil pump can drive the oil to the top of the engine during those chilly morning starts. The oil also has to be viscous enough to safeguard the engine when it gets to working temperature. This is where the use of modifiers in multigrade oil is advantageous when deciding on what oil to use.

Drawbacks of using a Motor Oil viscosity index modifier

Regrettably, Motor Oil viscosity index modifiers will have a few disadvantages. The main drawback is they are prone to mechanical shearing. When referring to the slinky analogy, it is easy to picture a stretched-out slinky cut in half by mechanical processes to create two smaller slinkys.

As the additive is consistently sheared, it will lose its capability to behave as a far more viscous fluid at increased temperatures. Greater molecular weight polymers create much better thickeners but have a tendency to have significantly less resistance to mechanical shear. Reduced molecular weight polymers are more shear-resistant, but do not enhance viscosity as efficiently at higher temperatures and, as a result, must be applied in greater amounts.

Though initially frequently only recognized as additives, Motor Oil viscosity index modifiers have become part and parcel of engineering motor oils to fulfill ever changing needs. Sign up to our RSS feed to keep updated on all oily issues.