Put a few drops of petrol from the nozzle on a Whatman 2 filter paper and let it dry. Pure petrol evaporates fully and leaves the paper clean. A stain or ring that stays points to something heavier mixed in. Every petrol pump must keep this paper and give it to customers who ask.
What the MDG says
MDG 2024 clause 1.4.1 (a): “Dealer to keep filter paper (Whatman 2) to check quality of MS. The filter paper should also be made available to customers on demand, if they wish to satisfy themselves of the quality of MS.” The outlet’s customer education board or poster should say so.
How to do it
- Ask the attendant for a Whatman 2 filter paper.
- Let a few drops from the nozzle fall on the middle of the paper.
- Hold it flat in the air, out of direct sun, and wait a minute or two.
- Look at the paper against the light.
Reading the result
| What you see | What it suggests |
|---|---|
| Paper dries clean, no ring | Nothing heavy mixed in |
| A greasy ring or stain stays | A heavier product, such as kerosene or oil, may be mixed in |
Limits
The test is quick and needs no equipment, but it is rough. It will not show a light solvent, and it says nothing about octane. A filter paper test failure is one of the reasons the MDG gives for oil companies to draw samples for the laboratory, through the three-tier sampling procedure.
Figures here are for reference. Your oil company’s certified calibration chart, approved instruments and the Marketing Discipline Guidelines always prevail.
Questions
Does the filter paper test work for diesel?
No. The MDG names it as a check on petrol (MS). Diesel itself evaporates slowly and leaves a mark, so the test tells you little.
Is a clean paper proof the petrol is good?
No. It catches heavier liquids like kerosene or oils. The density check against the invoice, and laboratory tests, catch more.