How Often Should You Change Your Engine Oil and Other Car Fluids?

The short answer (and why it's never that simple)

If you want one number to remember: most modern cars need an engine oil change somewhere between 10,000 km and 15,000 km, or every 12 months — whichever comes first. Older cars and those running mineral oil often need it closer to 5,000 km.

But the honest truth is that the "right" interval depends on how you drive, not just how far. Short trips around the inner suburbs, stop-start traffic on the Monash, towing a trailer to the coast, or leaving the car parked for weeks at a time all change the maths. Below is what actually matters, fluid by fluid.

Engine oil: the one that punishes neglect fastest

Engine oil lubricates, cools and cleans the inside of your engine. As it ages it gets contaminated with combustion by-products and loses its protective properties. Run it too long and you risk sludge, premature wear and, in worst cases, a seized engine — easily a five-figure repair.

Realistic intervals

• Full synthetic oil: 10,000–15,000 km or every 12 months.
• Semi-synthetic: 7,500–10,000 km.
• Mineral oil (older engines): 5,000 km or every 6 months.

When to shorten the interval

Your car is in "severe service" — and should be done more often — if most of these sound like you:

• Lots of short trips under 15 minutes where the engine never fully warms up.
• Daily stop-start traffic and long idling.
• Towing, carrying heavy loads, or frequent steep hills.
• Dusty or hot conditions, or a car that sits unused for long stretches.

A good rule of thumb: always replace the oil filter with the oil. Reusing an old filter undoes half the benefit of fresh oil.

Don't rely only on the dashboard oil light — by the time it glows red for pressure, damage may already be happening. Check the dipstick monthly: the oil should be amber to light brown, not gritty black or milky.

Coolant (engine coolant/antifreeze)

Coolant stops your engine overheating and protects against corrosion inside the cooling system. In Melbourne's summer heat, a tired cooling system shows up fast in traffic.

• Interval: typically every 2–5 years, or roughly 60,000–100,000 km depending on the coolant type (long-life OAT coolants last longer).
• Watch for: a sweet smell, the temperature gauge creeping up, or rust-coloured fluid in the overflow bottle.

Never top up a hot engine's coolant — wait for it to cool to avoid a dangerous pressure release.

Brake fluid: the safety fluid people forget

Brake fluid is hygroscopic, meaning it absorbs moisture from the air over time. Water in the system lowers the boiling point and can cause a spongy pedal — or brake fade when you need stopping power most, like on a long downhill.

• Interval: every 2 years, regardless of distance.
• Watch for: a soft or low-feeling pedal, or the brake warning light.

Transmission fluid

This one generates the most confusion because some manufacturers market "sealed for life" transmissions. In practice, fluid still degrades with heat.

• Automatic: 60,000–100,000 km for most cars; sooner if you tow or sit in heavy traffic a lot.
• Manual: 60,000–120,000 km.
• Watch for: rough or delayed gear changes, slipping, or a burnt smell to the fluid.

Power steering fluid

If your car has hydraulic power steering (many newer models are electric and have none), the fluid should be inspected regularly and changed roughly every 80,000 km or when it turns dark. Whining when you turn the wheel or stiff steering at low speed are the usual warning signs.

Differential and transfer case oil

Often overlooked, especially on 4WDs and utes. Diff oil typically needs replacing every 40,000–80,000 km, and sooner if you tow, go off-road, or wade through water. A whining or humming noise from the rear is a classic symptom of worn diff oil.

A simple maintenance rhythm

1. Monthly: check engine oil and coolant levels, plus tyre pressures.
2. Every 6–12 months: engine oil and filter change (based on your oil type and driving).
3. Every 2 years: brake fluid, and check coolant condition.
4. Every 60,000+ km: transmission, diff and power steering fluids as needed.

Your owner's manual is the final word on specific grades and intervals — but if you can't find it or the car's history is a mystery, a quick inspection clears it up fast.

Not sure where your car stands?

If you've bought a used car without service records, or you simply can't remember the last time a fluid was changed, it's worth getting everything checked in one go. Because we come to your home or workplace, there's no need to juggle a workshop drop-off — we can inspect and change your oil and fluids in your own driveway and tell you honestly what needs doing now versus what can wait.