Coolants are usually water based. These do a good job of controlling the temperature and removing the swarf from the grinding zone. When grinding cast iron, however, the swarf formed is very fine and powdery and does not settle out easily. This swarf tends to form a paste with the water-based coolant and loads up the grinding face of the abrasive, reducing the penetration of the grain into the part.

Oil based coolants are usually a mixture of equal parts of Pale Paraffin Oil and Mineral Seal Oil. They are used quite extensively in the grinding of cast iron to reduce the formation of the paste.

Oil is also used for the grinding of very heat sensitive materials. Because of oil's good lubricating qualities, less heat is generated. Disadvantages of using oil are that it presents a great fire hazard and that it is costly because of EPA Regulations concerning its disposal. Any grinder using oil as a coolant should be hooded with a good exhaust system, and have an automatic fire extinguisher directly over the grinder.

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