What oil does my car need?

All motorcars, whether boasting electric, or internal combustion, propulsion require lubrication to stop parts from rubbing together, overheating, wearing and failing. Oil is the most common lubricant used but they differ considerably, depending on the component.

While this blog provides a basic overview, modern cars have exacting lubrication requirements and so prioritise your car maker's specification, when selecting lubricants. Dosing any part of a motor car with an incompatible lubricant can cause mechanical failure and is likely to void the warranty.

What is engine oil?

Motorcar oil comprises base oils, based usually on crude oil. These are refined and combined by specialist chemical companies with additive packs to give the necessary performance characteristics.

What does engine oil do?

Engine oil lubricates and transfers heat energy away from highly stressed components. Most modern cars require synthetic oils, which tend to be those with high-quality base oils. Additive pack compositions vary considerably. Oils for classic cars tend to have fewer detergents, whereas those for diesel possess complex cleaning chemicals within their formulations.

The latest engines also need additives to protect their timing chains/wet belts, prevent low-speed-pre-ignition and curtail intake coking. Extra additives also protect rubber seals, neutralise harmful acids and reduce the natural tendency for the oil to turn into sludge, as it oxidises. This explains why engine oil needs periodic changing.

What is gear oil?

Gear oils are employed by manual transmissions and axles/differentials. Due to the high forces experienced between the gears, an extreme pressure lubricant tends to be required, hence why many of these products are labelled 'EP'. These additives account for EP gear oil's pungent smell; they also can be corrosive. This is why you should not deviate from the oil recommended by the carmaker. For instance, using a GL-5 lubricant in a component requiring GL-4 could corrode any soft metals used inside.

While draining and refilling transmissions tends not to be a service requirement, we are seeing an increasing number of Battery Electric Vehicles using special oils that require periodic replacing, due possibly to the high torque levels their transmissions must tolerate from the electric motor.

What is Automatic transmission fluid (ATF)

Used typically in traditional conventional torque converter, planetary-geared automatic gearboxes, the oil performs lubrication, cooling and hydraulic duties. ATF tends to run hotter than gear oil, making it more prone to thermal breakdown. Many manufacturers state that their transmissions do not require fluid changes but many specialists agree that doing so prolongs gearbox life considerably.

Most modern ATFs are classified by General Motors' Dexron ratings. Some classic transmissions use historic Ford specifications, which are not compatible, because they lack friction modifier additives. Dexron VI (from 2005) is backwards compatible with earlier types up to Dexron II (1978). However, Dexron ULV (Ultra Low Viscosity from 2014) is not.

Continuously Variable Transmission (CVT) employs either internal metal belts, or chains and has different lubrication requirements from conventional automatics.

Dual Clutch Transmissions (2CTs) also have bespoke lubrication requirements. Those gearboxes with internal 'wet' clutches (such as the Volkswagen Group 6-speed DSG) can get very hot and have mandatory oil change intervals, which you should follow.

What is hydraulic fluid?

While some cars use specially developed fluids, the most common type used is Central Hydraulic Fluid (CHF). This can be used by a variety of components, from power steering systems, to convertible roof systems. As with all oils, check your handbook to verify compatibility.

What is air conditioning oil?

The air conditioning system is lubricated by oil that is transferred around the system by the refrigerant. Topping-up the oil level is not a DIY task and should be left to an experienced air conditioning specialist, when the system is re-gassed.

Too little oil will reduce the system's operating life - too much will seize the compressor. The type of oil depends on the system - again - a specialist will know the specification and how much oil to add. Should you notice an oily stain around an air conditioning component, it may point to a refrigerant leak.

This information is only a basic guide about the various types of oil used on typical everyday motorcars. For specific information about which oil your car uses, consult your manual, main dealer, or parts supplier for advice. Newer and more specialist cars tend to have more exacting lubricant requirements, so be extra cautious.

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