Table of Contents


1. Overview

The SA agricultural sector spends around R12 billion on fuels annually, most of which is diesel (Agri SA, 2017). A fuel-tax rebate exists for VAT registered farmers, who can claim money back on their diesel purchases. Agri SA tells us that according to the Government Gazette No. 10584, farmers are entitled to 262 cents per litre on 80% of total eligible purchases (108 cents per litre fuel levy on 80% of eligible purchases, plus 154 cents per litre Road Accident Fund levy on 80% of eligible purchases). Find the Diesel Refund Guide, downloadable in pdf format, on

 What kind of engine oil should I use in my farm equipment?

The equipment owner should always select and use oil that at least meets the minimum API Engine Service Classification recommended by the engine manufacturer. Most gasoline engines require motor oils designated “API Service SG or better”. Farm diesel engines require oils designated “API Service CF-4 or better”.

What do you mean by “API Engine Service Classification” system?

This system, developed by the American Petroleum Institute, provides a guide for the selection of crankcase oils suitable for various service conditions. It classifies general ranges of engine service needs based upon:

  • engine design and construction
  • lubricating oil
  • operating conditions
  • maintenance practices
  • fuel characteristics

Here’s how it works. Each service class is designated by letters, the first letter being “S” for petrol and “C” for diesel engines. The higher the second letter the higher the performance level of the oil. This provides a convenient means for the engine manufacturer to indicate the service characteristics of his various engine designs and hence their lubrication requirements.

Do the SAE numbers define oil quality?

No. The SAE numbers refer to the viscosity of oil only, as defined in the SAE Crankcase Oil Viscosity Classification. “Viscosity” is a measure of the “resistance to flow”, or you might say it is the “body” or “thickness” of the oil. A poor quality oil can have the same SAE viscosity classification as a good oil.

How is multi-viscosity oil different from a single viscosity oil?

A multi-grade oil is one which meets an SAE viscosity requirement at both 0oC and 100oC. It does not thin out as much when heated or thicken up as much when cooled as a single viscosity oil. For example, SAE 15W-40 oils meet cold cranking requirements of SAE 15W at 0oC and high temperature viscosity requirements of SAE 40 at 100oC. Thus, a multi-grade oil stretches the usable temperature range. It provides easier cold-weather starting, quicker, more efficient lubrication, reduced engine wear, and better fuel economy.

How often should I change engine oil in my tractor?

If your tractor is in A-1 mechanical condition, operating on the recommended type crankcase oil, and under normal operating conditions, follow instructions in the owner’s manual. If any of the conditions vary greatly, the drain period should be reduced accordingly.

Does oil actually wear out?

The functions of the engine oil are to lubricate, cool, seal and clean. When an oil loses its ability to perform any of these functions, it is worn out. Contamination of oil occurs in all engines. The contaminants are unburned and partially burned fuel; fuel combustion products, including water; dirt and dust. These contaminants eventually destroy the oil’s capability to function efficiently. Oil should be drained before it reaches this condition. Engines will run better – longer, when the oil is changed as recommended.

How effective are oil filters, and how often should they be changed?

Oil filters should be serviced in accordance with instructions contained in the service manual. When properly serviced, they do an effective job of removing the larger solid particles contaminating the oil, thereby reducing wear and increasing engine life. Oil filters cannot, however, remove the need for changing the oil at proper intervals.

What can cause one oil to become excessively thick as compared to another when both are used at the same operating temperatures and loads?

Excessive thickening of lubricating oil in service is associated with the amount of contaminants it contains and how much the oil has oxidized. For example, solid contaminants such as finely dispersed carbon in diesel engine oils can cause severe thickening. The thickening of crankcase oil in service is generally associated with infrequent oil drain practices.