The Library of All Knowledge

Wrenchmonkey Series - Keeping your Cool (Cooling Systems)

The cooling system on a motorcycle is an excellent example of compromise. The need for efficient cooling competes for the need for light weight. For all of those riders who love air cooled bikes since "air doesn't boil", I have to say that liquid cooled bikes have more power since they can regulate combustion temperatures better.

Maintenance is simple. You should flush the radiator out once a year. When you do put some aluminum radiator flushing fluid and run the engine for about twenty minutes. Then drain and recycle the old coolant. When you put new fluid in use the stuff formulated for aluminum radiators Mix it with distilled water. Avoid using tap water since it can leave deposits all through the system which reduces the heat transfer capabilities. The exact ratio is open to debate. In cooler climates a 50/50 mix is preferred. But in hotter regions a 75/25 water/coolant mix is favored since water has better heat transferring properties. To help heat transfer and further prevent corrosion in magnesium parts you can add other additives such as Redline’s Water Wetter.

The mechanics of the system is simple too. The only major moving part is the water pump. During the your annual rebuild, take the pump cover off and wiggle the impeller. There should be no side to side movement. Also check the coolant for globs of oil. This may indicate that the water pump seal is shot. Also check to see if the transmission fluid is a milky white, this also may indicate that the seal is shot. Also take the cap to the dealer to see if it retains a seal under pressure. Also give the overflow hose a check to see if it still is open. Cut the end a 45 degree to help prevent jamming. Also note where the bleed bolts are located. On a Kawasaki KDX there is a bolt on the other radiator and at the top on the engine where the radiator hose enters the engine. When filling the radiator, crack open these bolts to let trapped air out. This will bleed out air pockets which can prevent the circulation of coolant.

Keeping the radiator working is also dirt simple. Keep the air flowing over the radiator and the heat gets sucked away. Clean the radiator of debris after every ride. If any if the fins get bent then CAREFULLY bend them back with a small pair of needlenose pliers. Do keep in mind that that can break the radiator I wouldn't suggest it until a whole lot of fins are bent since one bent fin doesn't make a significant contribution to the overall cooling system. Also if a stick or rock is punctures the radiator you can use two part epoxy to make an emergency repair. The best cure for radiator problems is preventative. Junk the stock plastic louvers and replace them with some serious aluminum guards. I use DeVol guard and I've taken some serious hits with no damage to the radiator (If can’t convince yourself to get the guards remember that the guards are about $150 CDN while the radiators are $300 CDN a side. You do the math.) To protect the hose, take old hoses, slit them lengthwise and zip tie them to new hoses.

Simple troubleshooting

Problem: Coolant flows out the overflow tube.
Cause: Possibly caused by a bad radiator cap. The spring is weak and lets coolant by at lower pressures. Other causes could be a bad head gasket, air trapped in the system or a stripped water pump gear. If it is a bad head gasket there should be evidence of burning in the gaskets.

Problem: Engine overheats quickly
Cause: Either the coolant is low or the circulation in blocked. The blockage can be from air or debris. It can be also caused by a stripped impeller.

Problem: A grinding noise on the right side of the bike that increases with rpm.
Cause: The water pump bearings and seals are worn.

Problem: The clutch slips and the transmission fluid is milky white.
Cause: The water pump seal is blown.

Problem: Coolant leaks from the rear of the cylinder head.
Cause: Chronic head gasket leaks are due to the strain placed on the head by problems with the frame. The shock twists the frame near the cylinder head mounting brackets. Then the misaligned brackets twist the head,