Gentlemen,

A friend of mine work in a Car Rental Company as a buyer. He share with me his company's lubrication problem :

The oil they use right now was claimed to fulfil as long as 10000 km oil change by the seller. Most car they have are Toyota (gasoline engine, 1800 cc) with engine oil capacity about 4 - 5 litres.

In reality, when it's about 8000 - 9000 km, the oil level is so low (only 1 litre left). The oil they use is mineral based.

I'm not yet suggest him to take the oil to be checked by oil analysis lab. But, can i claimed that this is one sign from low quality oil? (Low quality base oil and or VII with low shear stability index).

The oil supplier says it happens cause of cleaning process of the oil in the engines, probably because the use of low quality oil before using his oil (Honestly speaking, for me it's so absurd).

I hope for comments and suggestion. Especially what kind of lab test must be used to detect the real problem that triggered this sign.

thanx!

First, the cause of oil consumption may be oil evaporation or loss trough piston rings. There is a test that can be done to measure the evaporative rate of the oil (unfortunately, I dont remember the test name!). This parameter is dependent on the presence of lighter hydrocarbon molecules, in the blend. (synthetic oil perform better than mineral). For the loss trough the rings, there is no lab test but I have already saw that kind of problem: A customer change his oil brand and see a change in his oil consumption. When he goes back to the previous brand, the consumption goes back to normal. The cause may be ring hardness and configuration.
And remember. the oil change interval is not determined by oil brand (or sales rep) but by the manufacturer. Make sure that this oil meet the API specification. For 2001 and up, it should be API SM. Try an other oil that may be sightly more expensive, this MAY solve the problem.

The combination of low quality oils and engine wear will lead to oil consumption.

Some engines will burn oil no matter what. So, just pop that bonnet and use the dipstick. Top the oil off as needed.

And, if you can afford the better oils, by all means please use a name brand synthetic motor oil.