Firstly, lubricant(Oil or Grease in this case) is a substance used to reduce the frictional force between the moving parts. This process is known as lubrication. Lubricants come into various uses other than the main function. Like, reduce wear and tear of the machine parts, to cool the surface by carrying away the heat generated, for absorbing the shocks between bearings, reduction of noise. Lubricants also act as cleaning agents; any deposits present between the moving parts.

lubricant

So to decide which lubricant to use whether to use oil or grease is a debatable question and it depends on various factors:

Also Read: What Does Motor Oil Do To Automobile Engines? Why Does It Have To Be Changed?

CUT-SHORT POINTSOILGREASE
 

Start-Stop performance

There is a risk of a dry start as oil drains back to sump after machine shut down.Grease being thicker remains in the component where required lowering the risk of dry start.
 

 

Thermal convection

Oil flows freely enabling to carry away the unwanted heat. This reduces the risk of heat induces oxidation.When properly selected for the application being used, the temperature of grease will remain low.
TemperatureWhen the temperature of the system is very high temperatures.When temperatures are not excessively high.
SpeedHigh speed operating systemsModerate or low-speed systems
SealsOil tight seals are readily employedProtection is required from the entrance of foreign matter
LeakageOil is more prone to leakageGrease is less prone to leakage

As I said above it’s a debatable question which is better, There are certain points that we would like to share with you guys about lubricant:

  1. There are additives which are added to both oil and grease definitely to boost the performance. Graphite, zinc oxide is added to grease, these settle down and become difficult to filter. In the case of oil, we need to add soluble additives to control the performance and adhesive wear and abrasion.
  1. In case of gears and bearings, the energy and heat consumed by oils are very less as compared to grease.
  2. When the right amount of grease is lubricated to bearings, the churning loss is negligible. They push the unwanted amount of grease outside. While will continue to flow back which causes churning and heat.

    Also Read: 
    What Does Motor Oil Do To Automobile Engines? Why Does It Have To Be Changed?
  3. Thickeners clashing in case of grease, which may cause a change in the consistency of grease while oil does not add thickeners but the base oils and additive incompatibility when accidentally mixed.
  4. Oil volume can be controlled using level gauges while measuring grease volumes is impossible. Mostly over and under-greasing are the main concerns of bearing failures.
  5. Changing of oil is easy as compared to regreasing.