Hot engine? Leave the cap on
Never open the radiator or coolant cap while the engine is hot. The system runs under pressure, and the NRMA warns that boiling coolant and steam can escape and injure you. If the temperature gauge is climbing or a red light is on, pull over somewhere safe and switch off. Coolant is poisonous and tastes sweet, so keep children and pets away from any puddle. If someone has swallowed it, call the Poisons Information Line on 13 11 26. If they've stopped breathing or are unconscious, call 000.
How do you know it's coolant?
RAA lists green or orange puddles, a distinct smell after running, overheating, and white residue on the radiator cap or hoses. The colour varies by maker, and the NRMA says colour alone doesn't identify the right coolant, so a pink or blue puddle can count too. It usually feels a bit slimy, not oily.
The other sign is the coolant reservoir, the plastic bottle under the bonnet with MIN and MAX (or LOW and FULL) on the side. With a cold engine the level should sit between the marks. It shouldn't keep dropping. If you're adding coolant again and again and there's no puddle, the leak may be inside the engine, and the NRMA says those are harder to fix.
Clear water under the car on a hot day is usually the air conditioning, and that's normal.
Signs the coolant leak is getting serious
- The level in the reservoir falls between one week and the next.
- The temperature gauge sits higher than usual, especially in traffic or on hills.
- You can see a steady drip, not just a damp patch.
- The heater has stopped blowing warm, which can mean the coolant level is low.
- White smoke at the exhaust, or milky oil on the dipstick. That points to a head gasket.
What fixes a coolant leak properly?
It depends where it's coming from. RAA says a leak can start at any rubber cooling hose, any fitting, a gasket or the radiator itself. A perished hose or a loose clamp is a small job. A cracked plastic radiator tank usually means a new radiator. A leaking water pump, the part that pushes coolant around the engine, is a bigger job, and on some engines it's tied up with the timing belt, so ask if one is due.
Bottled stop-leak is the first thing many people reach for. Talk to the mechanic before you pour it in, because anything that can block a pinhole can settle somewhere you don't want it, and it doesn't replace the part that's failing. If you've already used one, say so.
Water alone is a roadside measure at most. RACQ says just adding water won't fix the problem, and refilling a hot engine with cold water can cause major damage. Coolant is more than water: the NRMA describes it as a mix designed to prevent boiling, freezing and corrosion. Use the type your owner's manual lists.
What to do today
Let it cool right down
Check the reservoir only when the engine is cold, without opening anything if the level is plainly visible through the side of the bottle.
Note what you see
Take a photo of the puddle and the reservoir level. Note whether the leak is worse after a drive or when parked overnight.
Top up only if it's safe
On a cold engine, use the coolant your manual lists, in the reservoir, up to the mark. The NRMA says most modern cars take coolant in the reservoir, not the radiator.
Watch the gauge on any drive
If it's a short drive to the mechanic, keep your eyes on the temperature gauge. If it starts to rise, stop. Don't push on to get there.
What will the mechanic check?
They'll start with a pressure test: a small hand pump on the cooling system, with the engine cold, to make a slow leak show itself. They'll check hoses, clamps, the radiator, the water pump and the heater core, and test the radiator cap, since a cap that doesn't hold pressure causes its own trouble. If nothing shows on the outside, they'll check for exhaust gas in the coolant.
A written estimate should name the part that's leaking, the coolant going back in and whether the system needs flushing. Ask whether the other hoses are the same age. Cooling systems are ordinary work for most mechanics, so you don't usually need anyone unusual, unless the leak turns out to be inside the engine.
What you can do, and what's the mechanic's job
You can
- Check the reservoir level on a cold engine.
- Top up with the coolant your manual lists, on a cold engine only.
- Photograph the puddle, and keep kids and pets away from it.
Leave to the mechanic
- Pressure testing to find the leak.
- Replacing hoses, the radiator or the water pump.
- Refilling the system and bleeding out the air.
Our take
We wouldn't sit on a coolant leak. It's usually a straightforward repair while the engine is healthy and a much bigger one after an overheat. If the level is steady and the gauge is normal, send the job this week. If the level is dropping quickly, we'd leave the car parked, and ask for a mechanic who can come to it.