Why Does Oil Loose Viscosity?

Your oil gets LESS viscous? We normally see the opposite effect. Are you using this in conjunction with a solvent such as benzene? Or perhaps at high pressures?

It gets dirty--It can be recycled by removing the impurities or re-refining it.

In an internal combustion engine blow-by combustion gases get past the rings and into the crankcase. Unburned gasoline can reduce oil viscosity. Also the shearing friction can break down the longer polymer chains that are added to increase viscosity.

A plethora of additives can be used in straight mineral oils, in order to give a specific oil its characteristics and make it suitable for a specific use.

What happens under normal conditions of use is that that after a period of time some of the additives start to break down or become choked, the oil then cannot perform its desired duties. This is why machinery manufacturers will specify oil changes at specific time periods before this breakdown in the additives occur.

Nothing actually happens to the base mineral oil, this remains the same, as I said the problem lies with the additives.

If a machine is operating incorrectly due to a mechanical fault or other problem this can cause an oil or the additives to "break down" before the recommended change period, this is why in many applications it is desirable to check oils regularly for signs of deterioration.

e.g. crankcase oils in diesel engines It is simple to check for fuel dilution, excessive carbon content and water, in between oil changes. One does not need to be "clever" to carry out these tests and the equipment required is very cheap.

Another area where oil quality is essential is hydraulic systems, it is estimated that 80% of hydraulic failures are caused by dirty oil. Correct filtration, care when topping up systems (put only oil not dirt into the reservoir), good breather filtration and regular laboratory sample checks on oil are essential.

Any rotating equipment generates tremendous heat & this heat tends to breakdown the additives in the oil. Generally equipment operate under various conditions & temperatures so in those situations accumulated dust & water is also a large culprit in this deterioration of oil. I normally advise my clients to change their engine oil esp cars every 5000 Kms even if the dealer insists to prolong the life of mileage. The mineral oils we use today in engines tends to breakdown quickly & if not replaced frequently can reduce the useful life of an engine.

viscosity mainly depends upon the internal molecular forces of oil molecules.

this forces depends upon :

1-temperature: as temperature increases that force start breaking hence its viscosity decreases.

2-water, unburnt carbon, diesel.

3-bacteria

As oil heats up and starts to break down and with added impurity's,it becomes thicker.

Hence the lower the viscosity.

Just a reminder RATSSTAR..................the base mineral oil does not break down, it is the additives that break down...........and the additives give the specific oil its properties.

If I assume that this inquiry is asking: Why does oil drop in viscosity when it's hot; then most responses are not applicable. Look at most common solids and liquids: Lard or animal fat is a solid at ambient temperature, but it liquifies with heat. Molasses, maple syrup, peanut butter all drop in viscosity when heated. For engine oil, one would prefer to have the oil stay at a higher viscosity when the engine is running, to properly lubricate the moving metal parts. But when the engire heats up, un-modified engine oil drops in viscosity and drains off metal parts more rapidly. Certain higher MW polymer additives, such as acrylics, are added to the engine oil to create the 5W30, 10W50 etc oils. At ambient temperatures, the polymer molecules are in a non-polymer like chemical environment, and the polymer molecules tend to curl up into little balls, which have little or no effect on the oil's viscosity. However, as the oil heats up, the polymer molecules open up and molecular enanglement occures, which artificially decreases the flow rate of the oil and increases the oil viscosity.

If I assume that this inquiry is asking: Why does oil drop in viscosity when it's hot

The way the question was worded does not imply to myself and others that it is asking why this occurs when the oil is hot.............so to my mind our answers are applicable.

Mind you the original question was poor.............so I guess one could ASS/U/ME anything.

Every vendor recommend to change the oil after some time of operation. One reason is because the vascosity is lower due termal and friction operation.

Ah, perhaps this is your question. By the way, you might talk with us.

Are you, by chance, referring to multigrade oil like 10W-30? If so, the 30 comes from additives (polymers) that thicken at higher temperatures. See the post #8 above. Those additives gradually break down so that you end up with SAE 10 oil and that does have less viscosity at high temperatures. Is this what you're asking?

air entrainment also. may be due to excessive foaming, due to mechanical reasons, incorrect oil level, and/or chemical additive depleted.