Changing your engine oil is one of the simplest and most important things you can do to keep your car running smoothly. Yet when it comes time to buy oil, many drivers find themselves staring at shelves full of bottles labelled 0W-20, 5W-30, 5W-40, full synthetic, semi synthetic, API SP, ACEA C3 and countless other terms that don’t mean much unless you’re a mechanic.
It’s no surprise that one of the most common questions people ask is, “What engine oil do I need for my car?”
The answer isn’t as simple as choosing the most expensive bottle or picking the same oil your friend uses. Every engine is designed with specific oil requirements, and using the right one helps protect internal components, improve performance and extend the life of your vehicle.
The good news is that choosing the correct engine oil doesn’t have to be complicated. Once you understand what the labels mean and where to find your vehicle’s recommended specifications, selecting the right oil becomes much easier.
In this guide, we’ll explain how to determine which engine oil your car needs, what viscosity ratings mean, the differences between synthetic and mineral oils, and the common mistakes you should avoid.
Why Choosing the Right Engine Oil Matters
Engine oil does far more than simply lubricate moving parts.
Modern engine oil performs several important jobs at once, all of which contribute to keeping your engine healthy.
These include:
- Lubricating moving components
- Reducing friction
- Carrying heat away from engine parts
- Cleaning internal engine deposits
- Preventing corrosion
- Protecting against wear
- Helping maintain fuel efficiency
Without quality oil, metal components inside the engine would grind against each other, generating excessive heat and causing rapid wear.
Over time, this can lead to expensive repairs that could have been avoided with proper maintenance.
Using the correct engine oil also ensures the engine performs as the manufacturer intended. Modern engines are engineered with tight tolerances, and even small differences in oil viscosity can affect lubrication, fuel economy and long-term reliability.
Considering an engine replacement can cost many thousands of dollars, choosing the correct oil is one of the cheapest forms of insurance you can buy.
How to Find the Correct Engine Oil for Your Car
Many drivers assume they need to memorise complicated oil specifications.
Fortunately, you don’t.
There are several easy ways to identify the correct oil for your vehicle.
Check the Owner’s Manual
The owner’s manual should always be your first reference.
Manufacturers specify:
- Recommended oil viscosity
- Oil performance standards
- Oil capacity
- Service intervals
These recommendations are based on extensive testing and should always take priority over generic advice found online.
If you’ve lost the manual, many manufacturers provide digital copies on their websites.
Look at the Oil Filler Cap
Open the bonnet and look at the oil filler cap.
Many vehicles have the recommended viscosity printed directly on the cap.
For example:
- 0W-20
- 5W-30
- 5W-40
While this won’t tell you every specification required, it’s often a useful starting point.
Check Manufacturer Oil Specifications
Viscosity is only one part of the equation.
Manufacturers may also specify particular performance standards such as:
- API
- ACEA
- Manufacturer-specific approvals
These standards ensure the oil meets the engine’s design requirements.
When buying engine oil, always make sure the bottle lists the required approval for your vehicle.
Understanding Engine Oil Viscosity
One of the biggest sources of confusion is the series of numbers printed on oil bottles.
For example:
- 0W-20
- 5W-30
- 5W-40
- 10W-40
At first glance, these numbers appear complicated.
They’re actually much simpler than they look.
What Does 5W-30 Mean?
Let’s use 5W-30 as an example.
The first number, followed by the letter “W”, refers to the oil’s performance during cold starts.
The “W” stands for winter.
Lower numbers flow more easily when the engine is cold.
This helps:
- Faster lubrication
- Easier starting
- Reduced engine wear during start-up
The second number refers to the oil’s thickness once the engine reaches normal operating temperature.
Higher numbers generally provide a thicker protective film at higher temperatures.
The goal isn’t choosing the thickest oil possible.
It’s choosing the oil your engine was designed to use.
Why Viscosity Matters
Engine oil that is too thick may:
- Reduce fuel economy
- Increase internal resistance
- Delay lubrication during cold starts
Oil that is too thin may:
- Provide insufficient protection
- Increase wear
- Struggle under high operating temperatures
Manufacturers carefully select viscosity grades based on engine design.
Following their recommendation provides the best balance between protection and efficiency.
Common Engine Oil Grades Explained
Although every vehicle is different, some oil grades appear more frequently than others.
0W-20
This low-viscosity oil is commonly used in newer petrol engines designed for maximum fuel efficiency.
It flows quickly during cold starts and reduces internal drag.
5W-30
One of the most common engine oils used across Australia.
It offers an excellent balance between cold-start protection and high-temperature performance.
Many petrol and diesel engines use this grade.
5W-40
This oil maintains similar cold-start characteristics to 5W-30 but provides slightly greater protection at higher operating temperatures.
It’s often recommended for turbocharged engines and some performance applications.
10W-40
More common in older vehicles and some higher mileage engines.
Its thicker viscosity at operating temperature can provide additional protection where appropriate.
Remember, these are general examples.
Always follow your manufacturer’s recommendations rather than selecting an oil simply because it’s commonly available.
Synthetic vs Semi Synthetic vs Mineral Oil
Another common question is whether synthetic oil is always better.
The answer depends on the vehicle.
Let’s look at the differences.
Full Synthetic Oil
Full synthetic oil is manufactured using highly refined base oils and advanced additives.
Compared with conventional oils, it generally offers:
- Better lubrication
- Improved high-temperature stability
- Superior cold-start protection
- Better resistance to breakdown
- Longer service life
Modern engines, especially turbocharged vehicles, often perform best with full synthetic oil.
Although it costs more upfront, the additional protection can provide excellent long-term value.
Semi Synthetic Oil
Semi synthetic oil combines mineral oil with synthetic components.
It provides many of the advantages of synthetic oil at a lower cost.
Benefits include:
- Better protection than mineral oil
- Improved resistance to heat
- Good everyday performance
- More affordable pricing
It’s commonly used in older vehicles or engines that don’t specifically require full synthetic oil.
Mineral Oil
Mineral oil is refined directly from crude oil and has been used for decades.
While modern mineral oils still provide adequate protection for suitable engines, they generally:
- Break down faster
- Require more frequent changes
- Offer lower performance in extreme temperatures
Many newer vehicles no longer recommend mineral oil.
However, some older vehicles continue to use it successfully when maintained correctly.
Which Type of Engine Oil Should You Choose?
There’s a common misconception that upgrading to the most expensive synthetic oil will automatically improve any engine.
That’s not necessarily true.
The best oil is the one that matches your vehicle’s requirements.
If your manufacturer specifies full synthetic oil, that’s what you should use.
If your engine was designed for semi synthetic oil, using the correct specification is usually more important than buying the highest-priced product on the shelf.
It’s also worth remembering that oil quality depends on more than whether it’s synthetic or mineral.
The correct viscosity and manufacturer approvals are equally important.
Choosing a reputable brand that meets your vehicle’s required specifications is almost always a better decision than selecting an unfamiliar product based solely on price.
Do Petrol and Diesel Engines Use Different Engine Oils?
Although some engine oils are suitable for both petrol and diesel engines, they aren’t always interchangeable.
Diesel engines operate differently and produce more soot during combustion.
As a result, diesel engine oils often contain additive packages specifically designed to:
- Handle soot contamination
- Prevent sludge formation
- Protect against higher combustion pressures
Petrol engines have different lubrication requirements and emissions systems.
Using the wrong oil may reduce performance or fail to provide the protection your engine needs.
Always check that the oil you choose meets your manufacturer’s specifications for your particular engine type.
Can You Use a Different Engine Oil Than Recommended?
This question comes up regularly, particularly when someone can’t find the exact oil grade recommended in the owner’s manual.
The answer depends on the situation.
In an emergency, using a similar oil that meets the correct performance standards is generally far better than running the engine with insufficient oil.
However, this should only be considered a temporary solution.
For regular servicing, it’s always best to use the exact viscosity and manufacturer specification recommended for your vehicle.
Modern engines are designed with very specific lubrication requirements, and even small differences can affect performance, fuel economy and long-term durability.
If you’re ever unsure, it’s worth asking a qualified mechanic before making the switch.
Is Thicker Engine Oil Better for Older Cars?
You’ve probably heard someone say, “If your car’s getting older, just use thicker oil.”
While there’s a grain of truth in that advice, it’s far from a universal rule.
As engines age, internal components naturally wear over time. In some cases, this can increase the clearance between moving parts, which may lead to higher oil consumption or lower oil pressure. That’s why some owners consider switching to a thicker oil.
However, thicker isn’t automatically better.
Using an oil that’s significantly thicker than the manufacturer recommends can reduce oil flow during cold starts. Since most engine wear occurs in the first few moments after starting, slower lubrication may actually increase wear rather than reduce it.
If your older vehicle is still in good mechanical condition, it’s usually best to continue using the recommended viscosity.
For engines with higher kilometres, many manufacturers and oil brands offer high mileage engine oils. These oils contain additives designed to help reduce leaks, minimise oil consumption and provide additional protection for ageing engines.
Before changing viscosity, it’s worth speaking with a trusted mechanic who can assess your engine’s condition rather than relying on general advice.
Can You Mix Different Engine Oils?
Another question that catches many drivers off guard is whether it’s safe to mix engine oils.
The short answer is yes, but only in certain situations.
Mixing Different Brands
If both oils have the same viscosity and meet the same manufacturer specifications, mixing reputable brands is generally acceptable for topping up between services.
Engine oils sold today must meet strict industry standards, so quality products are designed to work together.
Mixing Different Viscosities
Mixing a small amount of 5W-30 with 5W-40 during an emergency is unlikely to cause immediate damage.
However, it shouldn’t become a regular habit.
The final mixture may no longer perform exactly as your manufacturer intended.
Mixing Synthetic and Mineral Oil
Most modern engine oils are compatible enough that mixing synthetic and mineral oil won’t instantly damage your engine.
That said, you’ll lose many of the advantages of the synthetic oil by diluting it.
If you’ve had to top up with a different oil while travelling, there’s no need to panic. Just return to the correct oil specification at your next scheduled service.
How Often Should You Change Engine Oil?
Even the best engine oil doesn’t last forever.
Over time, oil becomes contaminated with dirt, combustion by-products and microscopic metal particles. Heat also causes the oil and its additives to gradually break down.
That’s why regular oil changes are just as important as choosing the correct oil in the first place.
The best guide is always your vehicle manufacturer’s recommended service interval.
However, several factors can mean your car benefits from more frequent oil changes.
These include:
- Regular stop-start city driving
- Frequent short trips where the engine doesn’t fully warm up
- Towing caravans or trailers
- Driving in dusty conditions
- High-performance driving
- Long periods of idling
These situations place extra stress on the engine and the oil, causing it to deteriorate more quickly.
Australia’s hot climate can also increase operating temperatures, making regular maintenance even more important.
If your driving falls into any of these categories, speak with your mechanic about whether shorter oil change intervals are appropriate.
Signs Your Engine Oil Needs Changing
While sticking to the recommended service schedule is ideal, your vehicle may also show signs that the oil is no longer performing as it should.
Watch for:
Dirty or Very Dark Oil
Engine oil naturally becomes darker over time as it collects contaminants.
Dark oil isn’t automatically bad, but thick, dirty or sludgy oil should be replaced.
Increased Engine Noise
Fresh oil creates a protective cushion between moving parts.
As oil deteriorates, you may notice increased engine noise or a rougher running engine.
Oil Warning Light
If the oil pressure warning light appears, don’t ignore it.
Low oil pressure can cause serious engine damage within minutes.
Stop driving as soon as it’s safe and investigate the cause.
Burning Oil Smell
A burning oil smell may indicate:
- An oil leak
- Oil dripping onto hot engine components
- Oil that’s deteriorated excessively
This should be inspected promptly.
Reduced Engine Performance
Old oil creates more friction inside the engine.
You may notice:
- Reduced responsiveness
- Rough idling
- Lower fuel efficiency
Although these symptoms can have many causes, degraded engine oil is one possibility.
Common Mistakes People Make When Choosing Engine Oil
Choosing engine oil isn’t difficult once you know what to look for, but there are still a few mistakes that can shorten an engine’s life.
Buying the Cheapest Oil Available
Price shouldn’t be the only deciding factor.
A quality oil that meets your manufacturer’s specifications provides far better value than saving a few dollars on a product that doesn’t.
Considering the cost of engine repairs, premium quality oil is relatively inexpensive.
Ignoring Manufacturer Specifications
Many people focus only on viscosity.
In reality, the required API, ACEA or manufacturer approval is equally important.
Two bottles labelled 5W-30 may not offer the same level of protection if they meet different standards.
Assuming Thicker Oil Offers More Protection
This is one of the most persistent myths.
The correct viscosity provides the best protection.
Using unnecessarily thick oil may actually reduce lubrication during cold starts and lower fuel efficiency.
Forgetting to Replace the Oil Filter
Changing the oil while leaving an old, contaminated filter in place limits the benefits of fresh oil.
A quality oil filter should generally be replaced during every oil change.
Waiting Too Long Between Oil Changes
Modern oils last longer than they once did, but they still have a service life.
Stretching oil changes well beyond the manufacturer’s recommendation increases wear and reduces protection.
How Much Engine Oil Does a Car Need?
Every engine has a specific oil capacity.
Smaller four-cylinder engines may require around four litres, while larger six-cylinder, eight-cylinder or diesel engines often need significantly more.
Always check your owner’s manual or service information before adding oil.
It’s just as important not to overfill the engine as it is to avoid running it low.
Too little oil reduces lubrication and cooling.
Too much oil can create excessive pressure, foam the oil and potentially damage seals or other engine components.
After adding oil, always confirm the level using the dipstick or your vehicle’s electronic oil level system.
Is Premium Engine Oil Worth the Extra Cost?
Many drivers wonder whether premium engine oil is simply clever marketing.
In many cases, higher-quality oils do offer genuine benefits.
Premium oils often provide:
- Better resistance to heat
- Improved wear protection
- Cleaner engine operation
- Better cold-start performance
- Longer-lasting additives
These advantages are especially valuable in:
- Turbocharged engines
- Performance vehicles
- Vehicles used for towing
- Cars driven in Australia’s hotter climates
That doesn’t mean every car needs the most expensive oil available.
The key is choosing a reputable product that meets your manufacturer’s required specifications. Beyond that, paying more doesn’t always translate into noticeable benefits for everyday driving.
Tips for Getting the Most Out of Your Engine Oil
Choosing the right oil is only part of keeping your engine healthy.
These simple habits can help maximise engine life.
- Check your oil level regularly, especially before long trips.
- Use a quality oil filter every time the oil is changed.
- Follow your manufacturer’s recommended service intervals.
- Fix oil leaks as soon as they’re discovered.
- Allow the engine to warm up naturally before demanding full performance.
- Use the correct viscosity and specification every time.
- Keep service records to ensure maintenance isn’t overlooked.
Small habits like these can significantly reduce long-term engine wear and help your vehicle remain reliable for many years.
Final Thoughts
If you’ve ever felt overwhelmed by the huge range of engine oils available, you’re not alone. With so many viscosity grades, specifications and product types on the shelf, it’s easy to assume choosing the right oil is complicated.
In reality, the safest approach is also the simplest.
Start with your vehicle manufacturer’s recommendations, choose an oil that matches both the required viscosity and performance specifications, and stick to regular service intervals.
Don’t be tempted by myths suggesting thicker oil is always better or that the most expensive product automatically offers the best protection. Every engine is designed with specific lubrication requirements, and following those recommendations is the smartest way to maximise performance, reliability and longevity.
Engine oil is one of the least expensive maintenance items your vehicle will ever need, yet it plays one of the biggest roles in protecting your engine. Spending a little time choosing the right oil today can help you avoid costly repairs tomorrow and keep your car running smoothly for many kilometres to come.