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Understanding Engine Oil.

All You Need To Know.

For almost 100 years Repco have been taking care of your vehicle by providing not just the car parts but the know-how and technical knowledge to keep you on the road. This expertise for all things automotive has led us to put together a range of questions commonly asked regarding engine oil to make it easy for you to choose, change or upgrade the oil in your vehicle. With help from our friends at Penrite, we aim to provide the little-known facts, general information, and clear up common misconceptions to give you the good oil when choosing the right motor oil for your vehicle.

What is the right engine oil for my car?

Vehicle manufacturers specify different oils for different vehicles and with a vast array of grades and viscosities it is important you get the correct product for your particular application. There are specific tools available at Repco to assist you in getting the right oil for your vehicle and these are as follows:

  • Registration Check on the Repco Website. Just type in your registration number and pick your state and our system will tell you the correct options for your vehicle. Not only will our Rego search function provide a comprehensive list of car engine oil and brands to choose from, it will also advise the sump / refill capacity. With modern 4WDs and commercials holding larger oil capacities this detail ensures you get the right literage for any vehicle to complete your oil change.
  • In-store – Our knowledgeable and helpful Repco staff members can look up the correct product for your vehicle as well as help you decide the best choice for your driving conditions. To assist them to get the right product they will need to know - Vehicle Make, Model, Year of manufacture, engine type (Petrol/Diesel), 4WD/2WD, Wagon/Sedan etc. If you operate your vehicle in climates or environments outside of the manufacturer's recommendations, we can provide the know how to purchase an oil that will stand up to the demands you place on it. Extremes of heat or cold, high performance vehicles or towing and heavy loads are just some of the variations that may require an oil to be recommended.
  • Penrite In-store Touchscreen - Located on Repco's Wall of Oil, the Penrite instore touchscreen is easy to use and will let you know not just the correct car oil, but all complementary Penrite products designed and suited to your vehicle. Just follow the interactive display and find the right product for your application.

Now that you know the multitude of resources to get the right answers for your oil requirements you won't be needing to fumble around in the glovebox looking for your owner's manual to find out.

How to choose engine oil?

Sometimes there may be more than several choices of suitable engine oils for your vehicle. So how do you choose between these? A critical question to answer is whether the vehicle requires an engine oil top up or whether you will be performing a full service? If it’s minor and a top up required, then the closest to the manufacturers specifications is a good choice. If you are looking at servicing the vehicle, then there may be several other choices you can make.

  • How many Kilometres has the vehicle travelled? High kilometres travelled may require a different oil to a low kilometre vehicle. As internal components wear, and seals and compression rings fatigue a thicker oil may provide added protection and less oil consumption.
  • Oil Type - Synthetic, Semi Synthetic or Mineral based product. Most modern engines require a Synthetic or Semi Synthetic blend to perform to the specifications provided by the manufacturer. Better flow rates, greater fuel economy and ability to stand up to greater variances in conditions are all some of the benefits of using a modern synthetic or semi synthetic option. Mineral oils are no less effective in their specified applications which usually consist of older vehicles with higher tolerances. Formulated with the relevant additive packages, mineral oils provide the lubrication and protection needed for older, less technically advanced engines.
  • Brand - Do you have a particular brand you like to use?
  • Cost – We all make purchases based on price and whilst it may seem like a bargain are you getting the best protection and long-term benefit from your oil. Irrespective of cost always ensure that the engine oil you purchase conforms to the specifications, additives and formulations advised by the manufacturer.
  • What oil is going to suit your driving conditions best. Sitting in stop start traffic for 90% of the time will vary greatly to the loads and conditions you would see whilst hauling a caravan on a holiday. Whilst being able to buy oils suited to a broad spectrum of conditions there are more application specific oils and formulations that will provide greater protection for their intended use.

When do I know it is time to change oils / How often should I change my oil?

Engine oil should be changed as per the vehicles servicing schedule. This is once again found in the servicing detail of your vehicles handbook or can be easily referenced online. These maintenance schedules are set out by the manufacturer to protect the vehicle and achieve the longest lifespan for the engine and drivetrain of the vehicle.

Exceeding the time frame / distance specified by the manufacturer when changing oil can lead to a multitude of problems such as;

  • Damaging of engine internals from lack of lubrication and viscosity breakdown. As oil degrades over time the lubricant and viscous properties decrease leading to metal on metal contact and increased component wear.
  • Oxidation of the oil which leads to the formation of harmful oil sludge inside the engine. The thick treacle-like consistency of the sludge makes it difficult for oil to flow between components increasing the chance of hot-spots or metal-on-metal contact and also adds increased resistance on rotating assemblies inside the engine. (see image)
  • Running out of engine oil, resulting in engine seizure. Skipping a service interval stretches the lubricant performance and can lead to early and short lifespans for engines. Engines both old and new burn oil in varying quantities and if left unchecked can fall below levels required to circulate via the oil pump and sufficiently lubricate your engine.
  • Engine cooling capabilities are compromised. At least 40% of your engine is cooled by your oil and not via the radiator and cooling system. This means that old or contaminated oil will provide less cooling capability than fresh oil. Sludge and oil build up is also detrimental to oil coolers that may become blocked thus increasing engine operating temperatures.
Understanding Engine Oil - Timing chain sludge

What happens if you mix engine oil viscosities?

Engine oils will generally mix together although the resultant mix may not provide the correct protection, economy, start up or operating temperature viscosity needed for your vehicle. It’s always best practice to say - When in Doubt, Flush it out. If you have mixed oils, this should be done for the shortest possible period until the oil can be fully flushed and the engine serviced.

What problems come from using the wrong oil / wrong viscosity?

Using the wrong specification engine oil can lead to many associated engine problems from sludging, seizing, noise, poor economy, oil burning, emissions failure, stalling etc. Using the wrong oil can also affect the vehicles warranty. Manufacturers spend large amounts on research and development to provide specific guidelines for their vehicle lubricants, whether it be a Specification, Viscosity, Base Oil Type or OEM approval. Using products outside of these guidelines runs the risk of manufacturers refusing a warranty claim based on not providing the protection and lubrication specified for that vehicle. What might seem like saving a few dollars on oil, could turn out to cost thousands of dollars in repairs.

Modern engines are designed to run higher or finer tolerances than older engines and using the wrong grade or viscosity will not provide the protection or oil coverage needed. Modern engines are also controlled and regulated by many sensors, DPF’s (Diesel Particulate Filter) and Catalytic Converters and using the wrong oil can block and damage these vital components, leading to many of the problems mentioned above.

How do I know when to change grades of oil from the manufacturer specs?

Generally, manufacturers will provide a viscosity chart and grade depending on the climate where the vehicle operates. In some circumstances a manufacturer will only have one specification and viscosity grade for their vehicle, and this does not allow for any changes in viscosity or specification.

A change in viscosity grade can be used on selected vehicles where the manufacturer allows multiple viscosities to be used. Changes generally occur when the engine starts to consume oil or becomes mechanically noisy.

Understanding Engine Oil - Temperature Range

What is the difference between a petrol oil and a diesel oil?

Both Petrol engine oil and Diesel engine oil are formulated from the blending of base oils and additives to achieve a set of desired performance characteristics. Diesel engine oil is designed to cope with the soot generated from the diesel combustion process and exhaust recirculation system, so contains higher quantities of dispersants and detergents to carry contaminants and prevent oil thickening. These additives also neutralize acids and clean the engine. Petrol engine oils do not need the same amount of dispersancy as the combustion process does not produce the same amount of soot. If Petrol engine oils had the same number of additives that were in Diesel oils, the detergents clean the cylinder walls and prevent proper lubrication of the engine affecting the seal between the rings and the cylinder liner resulting in a loss of compression and engine efficiency. Petrol engine oils contain other additives more in tune with the combustion process.

What is the difference between Synthetic Engine Oil, Semi Synthetic and Mineral Engine Oil?

Mineral oils are made from refined crude oil. Semi Synthetic use a mixture of Mineral and Full Synthetic Crude oil. Full Synthetic is manufactured from 100% synthetic base stocks. Synthetic oils are better at handling higher temperatures, are better suited to lower viscosity oils and have a higher viscosity index than mineral oils, meaning they flow better when cold. Full synthetic oil is produced by the refinement process of base oils to produce a more uniform structure of oil molecules. By having this purity ensures the performance of these engine oils to be more resistant to oxidation and break down at high temperatures which enables greater protection across a range of operating conditions. This uniformity of molecules within synthetic engine oil also provides longer life stability of the viscosity which protect against engine wear and oil consumption over time.

Does engine oil have a shelf life?

Engine oil lifespan very much depends on the way in which the oil has been stored. Generally, around 5 years with the container being unopened is acceptable but also the simpler the oil formulation the longer the shelf life. Penrite provide the batch number on their engine oils in the form of a white sticker that looks like a price sticker. If you need to know the date this was manufactured, you can ring Penrite and quote this batch number for confirmation.

What are the differences between a low-grade oil and a premium engine oil?

When you purchase engine oil, you generally get what you pay for. Low grade oils will normally use cheaper base stocks and cheaper additive packs. There specifications are normally inferior to a more premium oil and they rarely carry OEM approvals or industry Licensing.

It is possible to have two oils with the same viscosity, same specifications and one cost a lot more than the other. The difference is in their performance over the life of the service. The low grade one will have lower grade base oils, less synthetic base if it’s a Semi Synthetic, lower grade viscosity modifiers as against low shear modifiers used in the better oil. The low-grade oil will lose its viscosity faster which generally results in increased engine wear. Penrite pride themselves on using the latest technology coupled with only the best ingredients when formulating and blending their oils to give you complete protection for your vehicle.

Do engine treatments / additives adversely affect the performance of my engine oil?

Yes, engine additives can adversely affect the performance of the engine oil. Engine oils are a balanced mixture of base oils and a selected additive pack designed for a particular application. Adding in another product changes the chemical structure of the engine oil. The effects can be good or bad. This depends on the additive and the engine oil.

All Penrite oils are designed for their particular applications and if a specific additive is needed it will already be included in the correct dosage.

What happens when I overfill my engine oil?

Overfilling engine oil can cause oil foaming as it passes in and around the crankshaft when it is in rotation. This causes decreased performance as well as oil burning if too much oil is on the cylinder walls. Overfilling your engine oil can also lead to leaking around the main seals of your engine if the level is above the sump capacity. It is always suggested to regularly check oil levels as you undertake an oil change so as to not exceed the manufacturers recommended capacity. This capacity detail will be contained in your vehicle handbook and Penrite have an opaque line on their oil bottles to provide an easy reference to the volume you have used when filling. If overfilling has occurred, it is suggested not to start your vehicle but drain through your sump and refill to the correct level.

What does ACEA etc on the label mean and why is it important?

ACEA stands for "Association des Constructeurs Europeens dÁutomobiles". ACEA on the label will be followed by a specification that starts with a letter, either A,B C or E. The letters stand for;

  • A – Petrol
  • B - Light Duty Diesel
  • C - Catalyst Compatible or Catalyst Combustible
  • E - Heavy Duty Diesel

As an example, you could have ACEA A3/B4 or ACEA C3, or ACEA E6 or E9. It is very important in recognising the correct specification of an engine oil for your vehicle and using that for the performance and protection it provides. ACEA is the European equivalent of the API (American Petroleum Institute) yet has stricter and more severe requirements on their classifications. Hence an engine oil that meets both API and ACEA specifications uses a better additive package than one that is designed to meet only API specifications. Some oils may have an ACEA and API specification such as API SN/CF and ACEA A3/B4.

Can thin oil sufficiently protect an engine?

Thin or lower viscosity oil can protect engines if the engine is designed to run on these types of oils. Modern fuel-efficient engines are designed to run on lower viscosity oils as it improves efficiency and fuel economy, therefore reducing emissions. Engine oil technology has also improved, and lower viscosity oils provide outstanding protection for modern engines.

Under normal operating conditions an engine oil will display hydrodynamic characteristics in providing a layer of oil to separate two metal surfaces. As this load and speed is increased this in turn increases the friction and heat thereby decreasing viscosity of the engine oil. This is what is often referred to as thin film or boundary lubrication.

Understanding Engine Oil - Lubrication

Does my new car burn oil and how often should I check my oil?

All cars whether new or old burn some oil to a degree. Some burn more than others. They are designed to do this; however, each vehicle is different. There can be some large variations between brands and models. Burning some oil, may not mean that there is anything wrong with the engine or the oil in it. It is quite normal and modern oils are designed to burn efficiently through the combustion process. Oil levels should be regularly checked between services and if a top up is required it needs to be the correct specification and viscosity as recommended by the manufacturer.

What do the numbers on the bottle mean?

Gone are the days of engine oils solely being a classed as ‘monograde’ or single grade when it comes to their specifications. In the past monograde engine oils did not have the low temperature requirement that modern ‘multigrade’ engine oils do so would only be classed as an SAE 40 or similar. For an engine oil to be classified as a multigrade oil it will have both a high and low temperature viscosity to advise how they perform and protect under various conditions such as a 10W-40 engine oil. The first number will be its Winter (W) characteristics and the second number will refer to the hot or operating temperature of the oil.

The Society of Automotive Engineers (SAE) test oil and provide a grade or viscosity based on its ability to lubricate and flow at a pre-determined temperature. Using a numbering system comprising 0, 5, 10, 20, 30, 40, 50 and 60 allow oils to be categorised based on flow and the lower the number of the first the more suitable the oil is for lower temperatures usually found in winter.

Multigrade oils that comprise a cold starting weight need to flow at the following temperatures;

  • 0W oil will flow @ -35°C
  • 5W oil will flow @ -30°C
  • 10W oil will flow @ -25°C
  • 15W oil will flow @ -20°C
  • 20W oil will flow @ -15°C
Understanding Engine Oil - Viscosity

As the second number in a multigrade oil advises of the flow rate of the oil as tested at a ‘hot’ temperature of 100 degrees C it means that a 10W-40 grade oil is a 10-weight oil that will not thin more than a 40-weight oil when it gets hot.

Penrite have formulated their HPR and 10 Tenths ranges to contain EXTRA TEN technology to suit the harsh Australian climatic conditions found within our unique environment. This EXTRA TEN technology provides an increase in oil film strength, lower heat and friction characteristics that contribute to longer engine life. Especially suited for engines under load through towing or in extreme environments, EXTRA TEN reduces the rate at which oil thins when heated to provide maximum protection.

What is engine oil made of?

Engine oil is made up of a base oil and an additive package designed to suit the requirements and needs of the engine it operates in. Whether it be a mineral, semi synthetic or full synthetic oil these will all contain various additives in differing percentages. As can be seen below a typical oil could be broken down to show what they consist off.

Understanding Engine Oil - Oil Package

From this breakdown we can see the Viscosity Index (VI) Improvers and the additive package of a typical oil make up a relatively small percentage of its overall volume. Looking at the diagram below we can see that the elements of this additive package to contain;

  • Detergents and Dispersants – These elements both clean as they circulate but also enable the oil to suspend contaminants and oil by products to limit sludge and deposit build up.
  • Pour Point Depressant – This additive is added to enable the mineral or base oils to operate efficiently at low temperatures.
  • Anti-Wear Agents – Enable better protection from engine wear by providing a thicker oil film to surfaces.
  • Oxidation Inhibitor – Oxidation is when oil is subject to oxygen which promotes oil thickening. Oxidation is also increased with exposure to heat so an inhibitor will slow both the oil thickening and reaction to air.
  • Friction Modifiers – These are added to prevent internal engine friction whilst reducing scoring and wear.
  • Rust and Corrosion Inhibitors – Engine oils over time will develop and contain acids that rust and corrode metal surfaces. These inhibitors come in the form of acid neutralisers but also as barrier protection on exposed metal to provide a protective film.
Understanding Engine Oil - Additive Pack

Where can I get rid of used engine oil?

Oil recycling is an important step when looking at disposing of waste engine oil. At present Repco does not facilitate disposal of used motor oil but actively encourages customers to recycle used engine oil at their nearest recycling centre or used oil facility.

Referencing sites such as will provide a list of local centres or depots that can safely recycle and process waste oil to ensure it is kept from landfill. Disposing of sump oil correctly will ensure your used motor oil will gain a second life in all manner of applications such as Industrial Burner oil and being refined into Hydraulic Oil.

What do I need when changing my oil?

Now that you have chosen the right oil for your vehicle and application now is the time to reference our handy How to change your oil and oil filter guide. Providing a step by step rundown on all that is involved in completing this task it shouldn’t be beyond on the realm of most competent home mechanics to undertake.

Whilst performing this maintenance it also pays to check both the Coolant and other critical Fluid levels. Visual checks and top ups of these levels provide the satisfaction of knowing your vehicle is both safe and maintained to perform as the manufacturer specified.

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