Find a coolant leak

Home mechanic (basic tools) · Time: 30 to 60 min (estimate) (estimate)

Coolant can leak outside the engine (radiator, hoses, clips, water pump, drain bolt, reserve tank) or inside it (head gasket into the cylinder or into the oil). Outside leaks leave wet spots or dried coloured crust. Inside leaks leave no puddle but show as white smoke, milky oil or bubbles in the radiator. A pressure tester (a hand pump that pressurises the cold cooling system) makes small leaks easy to find; many workshops have one.

Safety

• Work on a cold engine. Never open the radiator cap hot.
• Coolant is poisonous and slippery. Wipe it off tyres and the floor.
• Keep fingers away from the fan; it can start with the key on.

You need

• A torch, a mirror, clean rags and white paper towel.

Steps

1. Check the level cold and note it: Check and top up coolant.
2. Clean the radiator, hoses and pump area with a damp rag so new leaks show.
3. Look at every hose along its length. Squeeze it gently when cold: hard, cracked, swollen or soft spongy hoses need replacing. Check each clip is tight and sits over the hose spigot.
4. Look at the radiator core and its seams, especially the bottom corners. Look for wet fins, crust or bent fins from stones.
5. Find the water pump (usually low on the engine, driven from the crankshaft or camshaft). It has a small weep hole under the pump body. Coolant or oil from the weep hole means the pump seal has failed; workshop job.
6. Check the drain bolt, the reserve tank and its hose, and the radiator cap seal.
7. Run the engine to normal temperature with a white paper towel under the engine. Stop and check for drops. Do not open the cap.
8. Look for signs of an internal leak: - white smoke that smells sweet and does not clear when warm - milky or creamy oil on the dipstick - bubbles or a strong exhaust smell in the reserve tank while running - coolant level falls with no outside wet spot
9. Ask a workshop for a pressure test if you cannot find it, and for a combustion gas test or leak-down test if you suspect the head gasket.

Check your work

• After repair, the cold level stays the same over several rides.

If it did not fix the problem

• Internal leak suspected: White smoke or steam from the exhaust and Do a leak-down test.
• Damaged radiator: Radiator is damaged, bent or blocked.