Understanding engine oil

How Do I Know When To Change Grades of Oil From the Manufacturer Specs?

The general rule of thumb here is you do not vary oil grades/viscosities from manufacturers’ recommendations. The main reason is factory warranty, because you don't want to use a different grade and have something go wrong and not be covered. Once the factory warranty period is over then things change. Your engine then has more kilometres on it, so has more wear and tear then when new.

The engine may start using more oil and smoking from the exhaust. The moving parts in the engine are worn and there is a larger gap between them. To help slow this oil usage a thicker viscosity oil can be used. It is designed for older engines and should only be used when the oil consumption is quite noticeable and you need to top up between oil changes. A lot of manufactures will have recommendations on this, apart from trying to upgrade you to a more modern vehicle.

The other reason for changing is climate. If you purchase a vehicle in farming country and then base it up on a mountain top in the snow fields, you may need a thinner grade oil. The manufacturer will also have recommendations on this. It always pays to check with them as they built the motor and therefore have the best understand of how the engine oil grades operate at different temperatures.

What Is the Difference Between a Petrol Engine Oil and a Diesel Engine Oil?

Both petrol and diesel engine oils can share the same oil base, it is the additives or quantities of additives they run that make the difference. This is due to the nature of the combustion process in both engines. Diesels are a dirtier engine and produce soot as a by-product of combustion, where petrol engines, while still producing soot, run cleaner and don't produce nearly as much.

Diesels need a higher concentration of some additives like dispersants and detergents to help break down the soot in the oil. The additives also help clean the engine and neutralize harmful acids. The difference in additives also impacts how by-products from the combustion process are handled by the engine oil.

You can use petrol engine oil in a diesel engine or put diesel engine oil in a petrol engine provided, and I repeat, provided the manufacture specifies it and the oil has the correct specifications such as API and ACEA.

What Are the Differences Between a Low-Grade Oil and a Premium Engine Oil?

When purchasing engine oil, there is a difference between a cheap 10w30 and a more expensive 10w30. When comparing, make sure they are the same type of oil, e.g., full synthetic or mineral. They are both a 10w30 as stated on the bottle, they have to be. The difference in price is usually due to the additive package found in the oil.

The cheaper oil may use less, or the minimum amount of the additive required where the expensive oil will have the full amount or add in an extra or more beneficial additive. This means the cheaper oil may break down earlier and not provide the best layer of protection for the engine. It may not even comply to certain specifications. As they say, you get what you pay for.

Do Engine Treatments / Additives Adversely Affect the Performance of My Engine Oil?

In today’s world, just buying a good quality engine oil that is designed for your car is all you need. There is no need to purchase an additional additive, especially if it is a fairly new car with not a lot of kilometres on it. Full synthetics especially are very good. As long as you do the required oil changes and change the oil filter, that is all that is needed.

There are exceptions to this where additives have their place. If you purchase an older car with high mileage or one that has not been maintained and serviced regularly, then additives may help.

Usually, an additive is designed to fix an issue, so you simply pick the one that suits your problem. However, there is never a guaranteed result with this method. It is cheaper than an engine rebuild and so it is often worth the investment, even if it simply reduces the issue.

If you drive your car on a racetrack, then an additive may also have a benefit. There are a lot of oils now that are designed for racing and handing the extra stress an engine goes through under extreme conditions, so using one of these may give your engine better performance in these scenarios.

What Does ACEA and API on the Label Mean and Why Is It Important?

These are found on oil bottles and in the owner’s manual for your vehicle. They tell you the oil specification that is right for your engine. You may find just one or both of these labels and they’re important in discerning the differences between oils.

ACEA - Association des Constructeurs Europeens dÁutomobiles

ACEA is a European automobile manufacturers association that rate oil suitability for different engines. It is found on the labels of lots of different branded oil bottles and tells you that this particular oil suits this type of engine. It gives you confidence the oil has the right additives to work well with the engine type. It will have ACEA on the label and will be followed by a letter, either A, B, C, or E.

These letters stand for:

• A – Petrol engine
• B – Light Duty Diesel engines with low level EGR (Exhaust gas recirculation)
• C – Engines with a DPF (Diesel Particulate Filter) or TWC (Three Way Catalytic Convertor)
• E – Heavy Duty Diesel engines

As an example, you could have ACEA A3/B4 or ACEA C3, or ACEA E6 or E9. The numbers after the A, B, C, or E are the particular revision, e.g., C4 is newer than C3. Each category is constantly being updated with changes in oil and engine technology.

API - American Petroleum Institute

API is an American organisation that sets oil suitability standards for diesel and petrol engines. Much like ACEA it tells you the oil’s suitability for an engine type. The system is not as easy to explain as the European system, so I have simply given you the labelling and revisions. It is more of a guide to say if you have an API standard for engine oil in your owner’s manual, use the oil bottle that has the same API standard on it.

Like ACEA, it will have API on the label and will be followed by a letter, either C, FA or S. The letters stand for:

• C (Diesel engines category C) — The latest revision is CK-4 and the previous one was CJ-4
• FA (Diesel engines category F) — The latest revision is FA-4
• S (Petrol engines category S) — The latest revision is SP and the previous one was SN

API have also released a standard ILSAC that has been developed with manufacturers. You may see this on American made vehicles. It will have ISLAC or API followed by the letters GF.

• GF — The latest revision is GF-6A and GF-6B (6B applies only to oils with a viscosity of 0W-16)

The Changes to Oil Over the Years

Engine oil has been around as long as internal combustion engines have been fitted to vehicles. Oil use has not changed, and it’s still necessary for the lubrication and cooling of moving engine parts.

Like the early vehicles though, it has evolved and is still evolving in the quest to reduce fuel economy and emissions produced by the engine; oil is becoming thinner to reduce friction and the time between oil changes is increasing.

Overall performance of engine oils is getting better, but this comes at a cost, as the prices are going up as well. Variety is increasing as well, and thanks to an incredibly large collector car market, most motor oil grades and viscosities are still available.

It’s likely that as new car manufacturers head down the electric path, car engine oil demand will start to slowly reduce, though it will be a long time before it is completely phased out.

With 100 years and counting under our belt, Repco has seen engine oil moving with the times, and we’ll be supplying your oil for a long time to come. So, head into a Repco store or shop online to find the right engine oil for you.