How do you test vegetable versus motor oil?

Answer 1

Motors can be run on vegetable oils, i.e. bio fuels.

Motor oil can be

1. Mineral oil
2. Synthetic oil(s)
3. Bio/vegetable oils

Therefore the terms vegetable oil and motor oil may mean the same thing.

A clearer distinction can be made between vegetable oilsand mineral oils.

Vegetable oils (esters) are made from plants, mainly from their seeds, e.g. rapeseed oil, olive oil, sunflower oil, linseed oil, lavender oil, tung oil, coconut oil, castor oil, etc.

Mineral oils (esters) are hydrocarbon based and are found in their crude state as mineral deposits in the earth, or are made from crude oil, coal etc by distillation.

Due to their respective sources, there are important chemical and physical differences between mineral and vegetable oils/esters, even between the different types of mineral oils and between the different types of vegetable oils.

Significant and more readily measurable differences:

Water content

Vegetable esters have a significantly higher ratio of water content than the esters in mineral oils.

Typical water saturation:

Vegetable esters -- 1000 milligrams per kilogram

Mineral oils - 60 milligrams per kilogram

For this reason, vegetable esters lose about 4% of their volume when heated to the boiling point of water (100 oC) whereas mineral oils typically only lose about 0.30% at the same temperature.

Viscosity

Vegetable oils have greater viscosity than mineral oils. Viscosity can be measured in different ways. One way is to see how long it takes the fluid at a given temperature to move through a pipe or hole of certain dimensions. To standardise matters, viscosity is measured in square millimetres per second (mm2/s).

The respective viscosities of common oils at given temperatures are known. e.g. viscosity of linseed oil at 38 oC is 27.2 mm2/s, but diesel oil is nearer 2.7 mm2/s.

Therefore a simple like-for-like comparison test between these two oils will quickly show which is the vegetable oil and which is the mineral oil.

Flash points

The flash points of vegetable oils are significantly higher than the flash points of mineral oils. (Don't try this at home!)

Vegetable oil such as canola (cooking) oil has a flash point of 327 oC, but a mineral lubricant oil may have a flashpoint of about 200 oC. The flash points of mineral oils vary considerably, but most of them have far lower flash points than vegetable oils.

Electrical bonds at molecular level

There are also differences in the way that the two oils (vegetable v mineral) react when subjected to electrical current. In typical tests, mineral oils break down in 3 to 5 minutes, whereas it may take 10 to 15 minutes to get similar results with natural (vegetable) esters.

SUMMARY

Some vegetable oils and mineral oils can relatively easily be distinguished from each other by smell or by sight/observation. (Tasting is not recommended!)

There are chemical differences between the two, some of which are indicated by the higher carbon-dioxide and sulfur/sulphur content of the gasses produced by ignition/burning.

Some of the tests such as those indicated above require heating, flame testing or wiring up to an electrical current. These tests may not be easy or safe to do at home or without proper supervision and attention to health and safety rules.

Often the container the oil came in will identify the type of oil it is.

SUGGESTIONS

If smell alone does not reveal the identity of the oil, one of the easier and safest methods of determining if a particular oil is vegetable or mineral is to measure its viscosity, oil's most significant physical quality.

There are various ways this can be done:

1. using a calibrated glass capillary viscometer

2. the rising bubble technique, using viscosity tubes

3. use of viscosity dip cups

4. using a rotary viscometer.

In the absence of such specialist equipment/apparatus you will need to devise your own means of determining viscosity.

In all cases you will need a thermometer, a timer, a calculator, and, of course viscosity tables against which to evaluate your results.

Of course, if you are testing a mineral oil that is a blend of oils or contains other chemicals which affect viscosity, this may make it very difficult to determine with certainty that the fluid is actually a mineral oil.