Volume 2 Issue 4 - Lubrication

Grease Lube Composition

Greases are made from oil and thickeners (sometimes called soaps). The process is simple but the details are fairly complex. The lubricating oil can be petroleum or synthetic and can vary in viscosity. Additionally, anti-wear and extreme pressure additives can be added to formulate greases for specific applications, such as, high speed bearings, very cold or very hot conditions, open gears, extreme loads or high moisture conditions, to name a few. Oil and thickeners can be combined to offer greater temperature ranges and resistance to moisture. Thickeners can be combined or formulated with additional chemicals to produce more complex thickeners for specific applications.

Greases will vary in thickness depending on the amount and type of thickeners used as well as the viscosity of the lubricating oil used. The National Lubricating Grease Institute (NLGI) is the regulating body that establishes specific ratings for greases. Greases are rated on a hardness scale from 000 to 6; where 000 is a thick liquid, like pudding, and 6 is a block, similar to hard clay. Today, 000 grease lube is used as a replacement for gear lubes in bearings and differentials and number 6 grease is used where a rubbing action is needed to produce a light film on the surface to be lubricated. Wheel bearings and chassis greases used in auto and truck applications are usually NLGI #2. In very cold climates NLGI #1 grease is preferred because the grease will thicken in response to the temperatures. Synthetic greases thickened with appropriate compounds are functional over a wide temperature range, from minus 50ºF to 500ºF; petroleum greases are generally limited to 0°F to 300°F.

In 1991,the NLGI developed a classification system specifically targeting automotive greases (Table One). For the majority of readers, it is the appropriate rating system for your truck applications.

NLGI Classification System for Automotive Greases (Table One)

So when you are looking to purchase grease lube for your truck, look for grease labeled GC-LB: grease rated for severe duty for the wheel bearings as well as for the chassis. Multi-purpose grease is the correct match for heavy duty pickups. Synthetic greases, available from Amsoil and Mobil will provide the best protection over the widest temperature range. Also, using synthetic multipurpose grease negates the need to buy moly-fortified heavy duty grease. Moly (molybdenum disulfide) is added to grease to provide extreme pressure lubrication. I have explained the difference in extreme pressure lubrication vs standard lubrication regimes in an earlier issue of Lube Notes, so please refer to that issue for the specific explanation. There are no legitimate extreme pressure grease points on heavy duty pickups, so save the heavy duty grease for larger equipment.

If the grease will be exposed to water, either by submersion or by spray, using water resistant grease is the best choice. To be water resistant, the grease must pass additional testing that insures its ability to cling to a surface while being sprayed with a stream of water. Water resistant greases contain additional thickeners and tackifiers that allow them to resist washing out. Sometimes, these greases will be labeled “marine” but more and more they are simple referred to as water resistant.