Car service

How do I find the best motor oil for my car?

Nothing works without lubrication. It is essential for an engine. A petrol or diesel engine consists of hundreds of moving parts, each with exactly defined properties. Many of this parts are subject to friction and without lubrication this would cause damage very soon. But adequate lubrication also requires adequate motor oil.

What needs lubrication?

Friction is especially important for those parts, coming into contact with other parts. These are, for example, the camshaft(s) with the valves, the crankshaft with the con-rods, the bearings and the piston rings along the cylinder wall. It is important to know that these parts have a so-called sliding fit, meaning that at normal engine temperature the parts are constantly in contact with each other and the working forces are not transmitted abruptly. Metal shrinks when cold and expands as it heats. In a cold engine there is a certain clearance between the parts. In older cars this can be heard by the ringing of valves and hydraulic tappets. As soon as the engine has reached its working temperature, all parts have expanded to the optimal sliding fit.

Good oil is important for cold engine

Meanwhile, motor oil has a very specific importance. In a cold engine, the oil collects in the oil carter. Decreasing temperature causes the oil to become thicker, or in technical terms more viscous. Even at low temperatures high-grade oil must be sufficiently liquid so that it can be pumped quickly to all potential friction surfaces.

What is the actual use of lubrication?

The engine components subject to friction have a special property: they are hardened. A finished component is made red-hot in an oven and subsequently cooled abruptly in an oil bath. This considerably hardens the surface, making it more resistant to friction. Once this hardened layer is worn away, further wear occurs very quickly. The part is as hard at its surface, as it is soft underneath. The hard layer has a depth of only several tenths of millimetres. With adequate lubrication this layer is maintained for thousands of kilometres. Without it, components become irreparably damaged after several hundred meters.

Good oil = expensive oil?

Basically, oil is never really bad. It might be more or less suitable for a specific use. Not so much the quality of the oil, but mainly the driving style and the frequency of oil change are essential. A wrong use of long-life motor oil can cause worse damage to an engine than frequently changed cheap oil. A certain quality-consciousness at purchase of motor oil is at any rate recommended.

Two tests, carried out independently by Auto Motor Sport and GTÜ had almost identical results: very often expensive motor oil has no decisive advantages over cheaper versions. The lubrication and temperature performance were almost similar. Testers do however agree that two factors need to be observed in oil purchase.

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Tips for purchasing motor oil

The most important thing when purchasing motor oil is only using the products approved by the car manufacturer. They issue a list of approved oils for their cars. The suitability is also printed on the oil containers. In addition to the viscosity and temperature information, such as 5W-30, 15W-40, etc., specific codes are printed on them, which should match the data of the car manufacturer.

As always, the temptation for certain “black sheep” exists to print the corresponding approval onto their containers. The worldwide trade over the internet makes it very easy to sell products of dubious quality.

Therefore, what counts for motor oil purchase is: use only known brands. The white oil containers from the 1-pound shop should be avoided at all cost, never mind the enticing prices.

What poor-quality oils may cause

When Toyota introduced the so-called lean-mix engine more than 20 years ago, enthusiasm soon changed into disillusionment. These engines were supposed to consume extremely low levels of fuel and therefore considered to be very economical in oil use.

In reality the outcome is completely different: the engines were totally polluted after several ten thousands of kilometres. Those lucky ones were able to save their engines with extensive rinsing and cleaning. Many engines perished completely and prematurely due to pollution.

The wrong lubrication, use of inferior oil or ignoring an oil change interval can have consequences just as drastic. Especially problematic in case of cheap oil is the occurrence of charring residue. This particularly hard residue resulting from burnt motor oil depositing on the valves and pistons.

This is very annoying in itself – though much worse is its consequence: charred remains sooner or later starting to drift can cause damage somewhere else, more specifically the catalytic converter. Its honeycomb structure with its narrow ducts is extremely sensitive to all unintentional pollution. It can gradually clog up, degrading its performance and more particularly the exhaust values of the car. Due to platinum being used in the construction of catalytic converters, the spare part is quite expensive.

Buy some other cheap motor oil

A sensible purchase of oil can save considerably more money than possibly could be saved by the use of cheap no-name brand oil. This implies choosing the right shop: a petrol station is generally the most unsuitable place for buying oil. The oil containers are extremely expensive at these points of sale and cannot be compared to the prices in the car accessory trade. The petrol station’s prices exceed those in the shop by at least 50 %.
A smart move is organising the purchase of motor oil with a few friends and acquaintances. The price depends for a great deal on the size of the container. If you should be able to buy an entire drum through your volunteers work, association or friendly circle, you can save a lot of money.

Long-life oil is the wrong option

Some years ago, Mercedes-Benz very proudly emphasised the quality of its engines, needing very few oil changes with long-life oil.

Our advice: Do not fall for these promises. An engine needs good oil as well as its periodical change. Only timely oil change ensures an optimal lubrication of all moving parts in the engine.

It is very wrong to skip an oil change and simply add oil instead. After long use, oil becomes thinner. Freshly added oil can’t compensate this. Thin oil doesn’t have the lubrication performance of fresh oil. Furthermore, it reaches the combustion chambers more easily where it causes the dreaded charred oil. Don’t forget to check and replace the oil filter if necessary.

Conclusion: pay no attention to false promises

Excess is harmful, especially when it concerns motor oil. Buy at the right points of sale, which offer a price advantage. You can save a considerable amount of money. In purchasing oil, trust the information supplied by the car manufacturer. There is no need for use of excessively expensive “premium” products. However: be conscientious and generous when changing oil. Expensive oil can maintain the engine, but never repair it. Once the camshaft is warped, the engine can only be saved by an expensive replacement of this part. With a bit of technical know-how and care this can easily be avoided.