A Basic Guide to Car Fluid Checks

Why Bother Checking Your Fluids?

Your car relies on a handful of liquids to keep it running smoothly, and most of them take less than five minutes to check. Yet they are the single most neglected part of routine maintenance for many UK drivers. A quick weekly glance under the bonnet, ideally before a long journey or when the weather turns, can catch a small problem before it becomes an expensive one. A low coolant level on the M6 or a brake fluid reservoir hovering near the minimum mark is not something you want to discover the hard way.

The golden rules apply to almost every check: park on level ground, make sure the engine is off, and give components time to cool. Have a rag or paper towel to hand, and never top anything up with a guess — your handbook will tell you the correct specification for your car. If you are not sure what a fluid should look like, check it when the car is new to you so you have a baseline.

Engine Oil: The Lifeblood of Your Engine

Oil lubricates, cools, and cleans the inside of your engine. Running low can cause wear that no service will undo, so check it at least once a month and before any long trip.

• Withdraw the dipstick, wipe it clean, push it fully back in, then pull it out again and read the level.
• The oil should sit between the minimum and maximum marks — roughly halfway is ideal. Never let it drop below the minimum.
• Check when the engine is cold, or wait ten minutes after switching off so the oil has drained back into the sump.
• Look at the colour: fresh oil is amber and translucent. Very black, gritty oil means a service is overdue.
• Top up in small amounts through the filler cap, rechecking as you go. Overfilling is just as harmful as running low.

If you find yourself topping up frequently, or see milky residue under the oil cap, get the car looked at — both can point to a bigger problem.

Coolant: Keeping Temperatures in Check

Coolant, often called antifreeze, stops your engine overheating in summer and freezing in winter. It flows through a sealed system, so the level should stay fairly stable. A steady drop means a leak somewhere.

• Never open the coolant cap when the engine is hot. The system is pressurised and scalding fluid can erupt.
• Check the level in the expansion tank against the min and max markings once the engine is completely cold.
• Top up with a pre-mixed coolant of the correct type for your car. Colours — pink, blue, orange — indicate different chemistries and they should not be mixed.
• If the level keeps falling, or you spot a puddle with a sweet, syrupy smell, book the car in.

Coolant should generally be replaced at the interval in your service schedule, often every few years, even if the level looks fine.

Brake Fluid: Small Drops, Big Consequences

Brake fluid is the one fluid you should never ignore. It transfers the pressure from your pedal to the brakes, and if it is low or contaminated, your stopping distance grows.

• Find the reservoir, usually a small translucent tank near the bulkhead, and check the level against the markings.
• A gradual drop as brake pads wear is normal. A sudden drop is not — that suggests a leak.
• Do not simply top it up to hide a falling level. Find out why it is dropping first.
• Brake fluid absorbs moisture from the air over time, which lowers its boiling point. Most manufacturers recommend a change every two years regardless of mileage.

If the pedal feels spongy or travels further than usual, stop driving and get the car checked straight away.

Screen Wash: The One Everybody Forgets

Screen wash is cheap and easy, yet it is the fluid drivers run out of most often — usually on a motorway in February. Road salt and grit smeared across the windscreen is a genuine safety hazard, and a plain water top-up will freeze in winter and do little to shift grime.

• Use a proper screen wash additive, never washing-up liquid, which strips paint and rubber over time.
• In winter, use a concentrated mix rated for well below freezing. In summer, a weaker dilution is fine.
• Top up the reservoir until it is nearly full, and keep a spare bottle in the boot.

While you are there, check your wiper blades. Worn rubber streaks and smears no matter how good your screen wash is.

Other Fluids and a Quick Routine

Depending on your car, you may also have a power steering fluid reservoir or a transmission dipstick. Many modern cars use sealed units, so check your handbook before assuming you need to do anything.

Build a simple habit: every Sunday, or before any journey over an hour, spend five minutes checking oil and coolant cold, brake fluid and screen wash at any time. Keep a rag, a torch, and a bottle of the correct oil in the boot. It costs very little, takes almost no effort, and it is the cheapest insurance your car will ever have.