Learning how to check your car fluids is one of the easiest maintenance jobs going — five quick checks under the bonnet take about ten minutes and can save you an expensive breakdown. Oil, coolant, brake fluid, power steering and screenwash all quietly do their jobs until one runs low. Here's exactly how to check each one, and how often to do it.
The 60-second version
- The five fluids to watch: engine oil, coolant, brake fluid, power steering fluid and screenwash.
- Check them on cool, level ground with the engine off — most have a dipstick or min/max markings.
- A quick monthly look-round and a fuller check before any long trip is all most cars need.
- If a level keeps dropping, that's a leak — book a car service in St Helens to find the cause.
How to check your car fluids, step by step
Before you lift the bonnet, park on level ground and let the engine cool for at least 30 minutes — hot fluids give false readings and can burn you. Then work through this simple routine.
- Open the bonnet and find the release catch (usually a small lever under the front lip).
- Locate each reservoir. Your handbook has a labelled diagram, but most caps are colour-coded or marked with a symbol.
- Check the oil with the dipstick (details below).
- Eyeball the coolant, brake fluid, power steering and screenwash against their min/max lines.
- Top up any that are low with the correct fluid, a little at a time, then re-check.
Do it when the engine is cold
Checking fluids first thing in the morning, before you drive anywhere, gives the most accurate readings — everything has settled and cooled overnight.
Each fluid: how to check, how often, and the warning sign
The steps differ slightly for each one. Tap through to see exactly how to check every fluid, how often, and the tell-tale sign it's low.
How to check each one
- Engine oil — pull the dipstick out, wipe it, dip it back fully, then read the film between the min and max marks.
- Coolant — look at the level in the translucent expansion tank against the min/max lines. Never undo the cap while warm.
- Brake fluid — check the level in the reservoir sits between min and max; the fluid should look clear, not dark.
- Power steering — most have a small dipstick in the cap or a marked reservoir; check against the lines.
- Screenwash — simply top up the washer bottle with a screenwash mix; there's no level to worry about.
How often to check
- Engine oil — monthly, and always before a long motorway trip.
- Coolant — monthly, and especially heading into summer or winter.
- Brake fluid — a glance monthly; it should be renewed roughly every two years at a service.
- Power steering — every couple of months, or if the steering feels heavy or whines.
- Screenwash — top up weekly in winter; running dry is an MOT failure point.
The warning sign it's low
- Engine oil — oil warning light, ticking from the engine, or the level near minimum.
- Coolant — the temperature gauge creeping up, or steam from the bonnet.
- Brake fluid — a spongy pedal or the brake warning light — get this checked immediately.
- Power steering — heavy steering and a groaning noise when you turn.
- Screenwash — the dashboard washer-empty light, or nothing coming out of the jets.
🚨 Never open a hot coolant cap
A warm cooling system is pressurised. Undoing the coolant or radiator cap while the engine is hot can blast out scalding fluid and steam, causing serious burns. Wait until it's completely cold — if the temperature gauge is high, leave it and call for help.
Which fluids matter most for safety?
They're all worth checking, but some carry more risk than others if you ignore them. Brake fluid and coolant top the list — one affects whether you can stop, the other whether your engine survives.
💧 Which fluid worries you?
Reading the oil dipstick
Pull it out, wipe it clean, push it fully back in, then pull it again and read where the oil film sits — keep it near the max mark, never below min. Unsure which oil to use or how often to change it? See our guide on how often to change engine oil.
Coolant that keeps dropping
Top up (only when cold) with the correct antifreeze mix. If it keeps falling or the engine runs hot, that's usually a leak or a cooling-system fault worth diagnosing before it overheats.
A soft brake pedal — act now
Low brake fluid or a spongy pedal can mean a leak or worn brakes, and it directly affects your ability to stop. Don't drive far — have it checked straight away with a car diagnostics check in St Helens.
Easy — the simplest one
Fill the washer bottle with a proper screenwash mix (not plain water, which freezes and grows bacteria). Keep it topped up in winter, as an empty bottle is an MOT failure. Nice job — that's one fluid sorted.
When to leave it to a garage
Topping up is fine for anyone, but a fluid that keeps disappearing is telling you something. A steady drop means a leak; milky oil or coolant can point to a head-gasket problem; and dark, old brake fluid needs proper replacement, not just a top-up.
If in doubt, the safest move is a professional check. The RAC's motoring advice pages are a good general reference, and for anything you can't diagnose at home, get in touch and our team can take a proper look.
Use the right fluid, every time
Oil grade, coolant type and brake fluid spec all vary by car. Check your handbook or ask us — the wrong fluid can do more harm than a low level. Never put water in the brake or coolant systems.
Not sure your fluids are right? We'll check the lot
Pop into Fastlane Autocare in St Helens and we'll check all your fluid levels and condition as part of a service — honest advice, no upsell. RAC & AA approved, Motor Ombudsman accredited.
Frequently asked questions
Six matter for most drivers: engine oil, coolant, brake fluid, screenwash, power steering fluid on hydraulic systems, and AdBlue on newer diesels. Gearbox and differential oils are workshop items rather than driveway checks. Run through the first four once a month and before any long trip, which takes about five minutes. Anything low deserves an explanation. Book a service in St Helens if a level keeps dropping, or ring 01744 808586.
Park on level ground with the engine cold, or at least twenty minutes after switching off, then pull the dipstick, wipe it clean, push it fully home and pull it out again to read. The level should sit between the two marks, ideally nearer the upper one. Cars without a dipstick use a dashboard menu reading. Top up in small amounts and recheck. See our oil and filter service and change intervals.
Check it first thing when the engine is stone cold and read the level against the minimum and maximum marks on the side of the expansion tank. Never unscrew the cap on a warm engine, because the system is pressurised and the contents are scalding. Top up with the correct pre-mixed coolant for your vehicle rather than plain water. A level that keeps dropping means a leak. See coolant services and what to do if it overheats.
Coolant comes in pink, red, blue, green and orange depending on the chemistry the manufacturer specified, and the colour tells you the type rather than the condition. What matters is matching what is already in the system, because mixing incompatible types turns the mixture to sludge. Brown, cloudy or oily looking coolant is a warning sign. Ask us which yours takes on 01744 808586, or book a coolant flush.
The brake fluid reservoir sits at the back of the engine bay with minimum and maximum marks moulded into the plastic. The level drops slightly as brake pads wear, which is normal, but a noticeable drop means either very worn pads or a leak in the system. Fluid should be clear to light amber, not dark brown. Book a free brake check and read about a soft brake pedal.
Most manufacturers ask for fresh brake fluid every two years regardless of mileage, because it absorbs moisture from the air over time and that water boils under heavy braking, giving you a long soft pedal. We test it with a moisture meter rather than guessing from the colour. It is one of the cheapest safety items on a car. Ask for the reading at your next service or ring 01744 808586.
Use a proper screenwash concentrate rather than water alone, because water freezes in the reservoir and pipes overnight in winter and can split them, and it does nothing to shift the oily film that road spray leaves on the glass. A washer system that does not work is also an MOT failure. Keep a bottle in the boot. Book your MOT in St Helens with us and we will check it beforehand.
Hydraulic power steering systems use a fluid reservoir, usually with a small dipstick in the cap, and the level should be checked with the engine off and the wheels straight. Cars with electric power steering have no fluid at all, which is most vehicles built in the last fifteen years. A whine on full lock is the classic low fluid symptom. See power steering fluid changes and steering repairs.
Get the car looked at rather than simply topping it up each month, because every fluid sits in a sealed system and a falling level means it is going somewhere. Oil can leak externally or be burned internally; coolant can escape through a hose or into the engine; brake fluid loss is a safety matter. A leak found early is usually a seal or hose. Ring 01744 808586 and see our page on oil leak repairs.
Gearbox and differential oils are workshop checks rather than driveway ones, because most modern boxes have a level plug underneath and need to be at a specific temperature to read accurately. Manufacturers describing them as filled for life mean the warranty period rather than the life of the gearbox. Changing the oil at sensible intervals prevents a lot of expensive faults. See our gearbox oil change service.
A red oil pressure lamp means stop the engine immediately and do not restart it, because it is telling you the oil pump is not maintaining pressure and bearing damage begins within seconds. It is a different symbol from the amber oil level warning some cars use. Check the level once the engine has cooled, then arrange recovery rather than driving. Read our page on the oil pressure warning light and ring 01744 808586.
Matching the specification matters far more than the brand, so two oils meeting the same manufacturer standard can be mixed safely in an emergency top-up. Coolant is less forgiving, because different chemistries react with one another and form deposits that block the radiator and heater matrix. When in doubt, top up with the smallest amount that works and get it checked. Ask us on 01744 808586 or book a service.
Every service we carry out includes checking and topping up the fluid levels, testing brake fluid moisture and coolant strength, and recording the readings on your report so you can see any trend from one year to the next. Engine oil and filter are replaced as standard. Anything losing fluid gets investigated rather than just filled. Compare what each level covers on our service cost guide or visit our workshop.