(1) Radiator fluids. Special coolants are better than water—although water can be used in a pinch. Most coolants use ethylene glycol as the main ingredient. This alcohol-based fluid can raise the 212-degree boiling point of plain water by as much as 60+ degrees. A coolant is also called an antifreeze, because it drops the freezing point down to -80 degrees. Inhibitors are added to coolants to control corrosion. Silicates aid in the lubrication of water-pump seals. Defoamers maintain the consistency of the coolant as it’s being whirled around by the impeller.

(2) To distill or not. If you want to put water in your radiator, it is best to use distilled water. Distillation is a process that boils the sediments down, so the rising steam vapor can be collected. The liquid in the vapor is the purest form of water you can buy. By using distilled water, you eliminate the impurities and hardness that scrapes, scars and corrodes the cooling system.

(3) Fluid height. How high should you fill your radiator? To the top. If the fluid level drops by even a small amount, start looking for the leak. The most likely places are head gaskets, hoses, radiator caps or water-pump seals.

(4) Radiator cap tech. The stiffness of a radiator cap’s spring determines how much pressure the water is under. A broken gasket or weak spring means the cap can’t stop the water from boiling. Water will boil at 212 degrees Fahrenheit; however, a cooling system that is placed under 15 pounds of pressure will allow straight water to reach 250 degrees before it boils. The simplest way to avoid boiling your engine is to drop-kick the stock 1.1kg/cm2 radiator cap for a 1.8-or-higher cap from Twin Air or CV4. Every radiator cap has its pressure limited printed in or stamped into the cap.

(5) Troubleshooting radiators. Overheating can be caused by a faulty impeller, coolant blockage, old coolant, lean jetting, a thrashed top end, a blown head gasket or a bad radiator cap. Anything that impedes the speed with which the coolant flows through the radiator will cause the engine to overheat. If you suspect a leaking water-pump seal, a quick check of your gearbox oil will tell you if water is leaking into the tranny. Oil with water in it looks like milk. Finally, a blown head gasket can leak exhaust gases into the coolant and pressurize the system so much that it triggers the radiator cap’s blow-off.(6) Can I race with low fluid? This is a personal call. If you can’t see any coolant in the radiator, park it and have it fixed. If the level has dropped to the top of the inner core structure, you could try to race, but first borrow a radiator cap from a buddy. Fill the radiators up and have a friend signal you if he sees steam coming from the overflow. This is a personal call, but very often coolant levels drop with use. It is best to get the coolant system checked by an expert.

(7) Can I test my radiator? Yes. You can buy a coolant-system pressure tester. It replaces the stock radiator cap and has a built-in pump to inflate the system to the maximum pressure listed on the radiator cap. Coolant will leak from wherever the fault is. If the coolant system holds the maximum pressure for 10 minutes, you’re fine. 

(8) Can radiators be welded? Yes. A local radiator repair shop that has experience with aluminum radiators can successfully weld a cracked tank or spigot. Leaks in the core are harder to deal with. MXA sends its radiators to ICW Radiators for any major repairs. You can reach them at

(9) Radiator guards—good or bad? Anything that impedes airflow is bad, but sometimes you have to trade cooling for protection. MXA runs mesh-style Twin Air or Moose radiator sleeves to keep mud out. We don’t worry about tree branches and other obstacles on motocross tracks. Never run those road-warrior aluminum radiator guards. They restrict airflow and raise the engine’s operating temperature.

(10) How do you clean a radiator? You can use a pressure washer or good old-fashioned elbow grease, but both methods require caution. The goal is to clean the open spaces between the radiator fins. Spray the radiator fins with water, and then take a soft-bristle brush and skim the dirt off by brushing from side to side—in the same direction as the fins. Don’t brush the radiator fins with an up-and-down motion, because the paper-thin fins easily bend, which will make them restrict airflow just like mud.


antifreezebad radiator capblown head gasketcoolant blockageCV4distilled radiator waterfaulty impellerlean jettingmotocrossmxamxa tech specold coolantradiator capradiator fluidthrashed top endtwin airTwin Air radiator sleeves