Coolant is usually green, blue, pink or orange and smells sweet. A leak shows as drips under the bike, wet hoses, crust at joints, steam, or a reserve tank that keeps needing top-ups. Outside leaks come from hoses and clips, the radiator, the water pump seal (it leaks from a small weep hole), the drain bolt, the reserve tank or the radiator cap seal. If the level falls with nothing visible outside, coolant may be leaking inside the engine.
Is it safe to ride?
Not until the leak is found and the level is correct. A bike that loses coolant overheats, and coolant on the rear tyre is slippery.
Quick checks first
- Wipe the liquid with white paper: coloured and sweet smelling?
- Engine cold: check the reserve tank level.
- Look at hoses, clips and the radiator bottom.
- Is the rear tyre wet?
- Coolant pushing out of the radiator cap while the engine runs can mean combustion pressure is entering the cooling system (head gasket or cracked head).
Diagnose it step by step
1Is the liquid really coolant?
- Oily brown: Oil leaking under the bike.
- Clear water drips from the exhaust when cold: normal condensation.
- Clear water from the air conditioner of a car parked nearby, or rain: not your bike.
- Coloured and sweet: go to step 2.
2Engine cold, check with Check and top up coolant. Is the level low?
- Yes: top up to UPPER and go to step 3.
- No: the leak may be from the reserve tank overflow after hot running (a little is normal if overfilled). Recheck after a ride.
3Trace it with Find a coolant leak. Where is it?
- Hose or clip: tighten or replace the clip or hose. Retest.
- Radiator core or seam: go to Radiator is damaged, bent or blocked.
- Water pump weep hole: the pump seal has failed. Workshop job; ride only after repair, because the seal can also let coolant into the oil.
- Drain bolt: fit a new sealing washer when you Replace the coolant.
- Thermostat housing: workshop, see Check the thermostat.
- Nothing outside: go to step 4.
4Is the oil milky, or is there white smoke?
- Yes: internal leak. Go to Oil is milky or creamy or White smoke or steam from the exhaust.
- No: ask a workshop for a pressure test and Do a leak-down test.
Do not add leak-stop products unless the maker approves them. They can block narrow radiator tubes.
Causes, most likely first
| Cause | How to confirm | Fix |
|---|---|---|
| Loose clip or perished hose | Wet hose end | Find a coolant leak |
| Radiator damage | Wet core, stone damage | Find a coolant leak |
| Water pump seal | Weep hole wet | Workshop pump repair |
| Drain bolt washer | Wet at bolt | Replace the coolant |
| Head gasket (internal) | Milky oil, white smoke | Do a leak-down test |