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Book Bits

From the book "Lubricants and Lubrication":

Long-life and reliability are the criteria for the commercial vehicle sector. The HD (Heavy Duty) oils have to match these requirements. The predominant requirements are the dispersion of large concentrations of soot particles as well as the neutralization of sulfuric acid combustion by-products. Performance is also judged by piston cleanliness, wear and bore polishing. Oxidation and soot-related deposits, mainly in the top ring groove lead to poor piston evaluations and an increase in wear. This, in turn, leads to the abrasion of the honing patterns in the cylinders, a problem better known as bore polishing. The result is increased oil consumption and poorer piston lubrications because the oil cannot be trapped by the honing rings. Inadequate soot and sludge dispersion as well as chemical corrosion can lead to premature bearing wear. And finally, advanced turbocharged diesel engines have also been evaluated. Blow-by gases always carry some oil mist into the exhaust and turbochargers are very sensitive to unstable oil components.

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Today's Tip

• Inclined or vertical shafts can lead to grease escaping from the bearing due to gravity. This will eventually lead to lubricant starvation and eventual premature failure of the bearing. Consider using a grease with good adhesive properties of penetration class 2 to 3. In addition a baffle plate, mounted in the housing below the bearing, will help to retain the grease where it is needed - in the bearing. (Tip submitted by Derek Peasley, FAG Sales Europe. Thanks Derek!)

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Q & A

"I am aware that many grease thickener types are incompatible when mixed. However, if I use two greases with compatible thickeners, but different brands, how do I know if the additives and base oils are compatible, or does it matter?"

In critical applications it matters. Remember grease is not a thick oil, it's an oil with a thickener. The base oils, viscosities, and additives used in grease can vary considerably, even between general-purpose greases. As such, there may be a loss of performance (antiwear, antioxidation, antirust, etc.). This is a risk that may not be worth taking. Unlike grease thickener incompatibility, the effects of additive incompatibility may be considerably less obvious and contribute to problems over a longer period of time.

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