What should I do if the coolant warning light comes on?
If the coolant warning light comes on while you're driving, find somewhere safe to stop as soon as you reasonably can and switch the engine off. Don't open the coolant cap while the engine is hot — a pressurised system can cause a nasty scald. Once it's cooled down, check the level if you know where to look, and if it's clearly low or you can see or smell coolant, get the car looked at before driving it any real distance.
Is a coolant light the same as the temperature gauge reading hot?
No, and the difference matters. The coolant warning light usually means the level in the header tank has dropped below a sensor, which can be a slow drip, not an emergency on its own. The temperature gauge reading into the red is different — that means the engine itself is currently too hot, and that's a stop-the-car-now situation, not a book-it-in-next-week one. If both are happening together, treat it as the more serious of the two.
Why would coolant be low in the first place?
Coolant doesn't get "used up" by driving the way fuel does. If the level keeps dropping, something is letting it out — a small weep from a hose, a radiator, the header tank itself, or the water pump. None of those are visible from the driver's seat, and none of them get better by themselves. A system that's slowly losing coolant now is usually the same system that will lose it faster later.
Can I just top it up and carry on?
You can top up as a short-term measure if the car is a known distance from help and the level is only slightly low, using the correct coolant type for that car — the wrong type doesn't mix well with some systems. But topping up treats the symptom, not the leak. If you find yourself topping up more than once, that's the car telling you where to look next, which is at a garage, not at the top-up bottle.
What happens if I ignore it and keep driving?
An engine that overheats can warp a cylinder head or blow a gasket in a short space of time, and that's a dramatically more expensive repair than whatever caused the coolant to drop in the first place. A warning light is cheap information. Ignoring it and hoping is the expensive option, not the convenient one.
What does ONEFIX check when a coolant light comes in?
Every service at ONEFIX includes a free digital health check with photographs, which covers the coolant level and visible condition of hoses and the radiator as a matter of course. If the light has come on outside a service, it's worth booking it in as a look rather than waiting for the next one. We check the level, look for where it's actually escaping from, and pressure-test the system if needed to find a slow leak that isn't obvious by eye — and you get a price in writing before any repair starts, because we don't do work that hasn't been approved.
Will I be charged just to have it looked at?
Where something needs inspecting rather than booking as a straightforward fixed-price job, we tell you what we've found and put a price in writing before touching anything. You can say no to that quote and the car is yours to take elsewhere. You only pay for work you've actually agreed to.
Should I drive to the garage with the light on?
If the light is on but the temperature gauge is reading normally and there's no visible leak or smell, a short, careful drive to get it checked is usually reasonable. If the gauge is climbing, if you can see or smell coolant, or if there's any sign of steam, don't risk the drive — call the garage from where you are instead of pushing on.
How do I book this in?
Book online with your registration and a note that it's a coolant or cooling system concern, or call the garage directly and describe what you're seeing. If you're not sure whether it's urgent, call first — it's a five-minute conversation against a much longer repair if it's left.
See also our guide on what an MOT advisory means if a cooling system note has appeared on a recent MOT certificate.