Engine coolant performance deteriorates over time. This can be caused by a build-up of aluminium corrosion or a change in the fluid to coolant ratio when periodically topped up. Most coolants contain special ingredients to help keep the solution alkaline. Over a period of time these lose their effectiveness, so the coolant should be changed at least every two years regardless of mileage.
What you are dealing with
All bike engines are made from aluminium alloys so ensure your coolant is specifically for alloy engines. The capacity of the coolant system can vary from bike to bike – check the owner’s handbook for capacity – but 3-4 litres is typical. Note that coolant that is sold as antifreeze needs to be diluted with distilled water. The usual ratio is 50:50, but it’s worth checking on the container’s instructions. Otherwise, coolant comes as a premixed solution ready to pour straight in.
Stuff you’ll need
Enough fresh coolant, or antifreeze and distilled water to mix, and a funnel to refill the system. Various screwdrivers and Allen keys to remove fairing panels, and sockets or ring spanners to remove the main drain bolt. A tray, or disused kitchen sink bowl to catch the old draining coolant, plus some absorbent material in case of spillage.
What can go wrong?
You could get scalded if the engine has been running – the system becomes pressurised and hot coolant will erupt when any cap or bolt is undone. A slow death could occur if you swallow antifreeze – it contains ethylene glycol, which is highly toxic.
Don’t even think about it if...
You haven’t got at least an hour to spare to do the job, or you’re the sort of person who tops up your car’s washer bottle with antifreeze.
What skills do I need?
Basic mechanical aptitude is enough. Although it’s really not the sort of task to think about attempting if you’re nursing a hangover…
1. Get the bike upright on a paddock stand. You need to gain access to the radiator cap, drain bolt and the header tank cap so, on a sports bike, you may need to remove most of the fairing. If the drain bolt is mounted on the sidestand side of the engine put the bike on its sidestand to help drain all the coolant out.
2. As a general rule, most drain bolts are located at the lowest point of the cooling system near to, or actually on, the coolant pump housing. Some bikes don’t have drain bolts, so removing the lowest hose is the only way to drain off the coolant. Before undoing anything ensure the engine/coolant system is cold.
3. Place a drain tray or old bowl under the drain bolt. Carefully loosen and remove the radiator cap to relieve any pressure in the system and allow the coolant to flow unhindered. Undo the drain bolt a few turns and make sure the sealing washer (if fitted) is loose on the bolt. Now remove the bolt and washer completely.
4. Once the flow of coolant has finished, wipe clean the area around the exit hole, and the bolt and washer. Refit the drain bolt and sealing washer – if the washer looks damaged (with nicks, splits, etc) then replace it. The bolt needs to be torqued tight – refer to manual or a dealer for the torque figure.
5. If there is any coolant left in the header tank, remove and drain, and clean out any residue before refitting. Now arm yourself with a funnel and coolant. If diluting antifreeze it should be done with distilled water or boiled kettle water – tap water contains minerals which will clog up the inside of the rad.
6. With the funnel in place in the radiator top, slowly fill with coolant, as it will inevitably overflow when the system is full. Stop every now and then to allow trapped air to escape from the radiator. Gently squeezing exposed hoses helps purge any air. Add coolant until the level reaches where the bottom of the rad cap will sit when fitted.
7. Refit the radiator cap. Now add coolant to the header tank, filling it so the level sits half way between the upper and lower level marks. Some bikes may have ‘bleed’ bolts on the coolant pipes to remove pockets of air out of the system, so loosen them one at a time until coolant appears, then tighten shut.
8. Start the bike and let it idle for 30 seconds. At the same time take the chance to look around the bike to make sure nothing is leaking. Running the engine for this short amount of time should be enough to dislodge any further trapped air via the header tank without getting the coolant too hot.
9. Remove the radiator cap and check the coolant level. Top up as necessary. Check the level of the header tank. If it has emptied completely then you need to repeat stage 8; otherwise top it up to the upper level line and replace the cap. Be careful when replacing the cap as it is all too easy to put it on cross-threaded.
10. Again start the engine and let it warm up to the point at which the cooling fan comes on. Then switch off. While waiting – go for a cup of tea or do the shopping – for the bike to cool down check again for any leaks. When the motor has cooled down re-check the header tank level and, if needs be, top it up.
11. Before refitting any bodywork, soak up any spilt coolant on the floor or bike with absorbent cloth/kitchen paper – it can corrode plated metal parts and it is slippery stuff. Ideally wash down affected areas with soapy water. Any antifreeze or coolant left over must be stored out of reach of children/animals/idiots.
12. Take the bike for a ride and when you come back recheck the level in the header tank. The ACU states it is illegal for race bikes to have glycol-based coolant in the bike’s system (very slippery when dumped on the track) so the above method can be applied to track-only bikes by substituting the coolant with 100% distilled water.