Radiator Caps

Overheating – Radiator Cap

The bike temperature was 109 degrees Celsius. We were out in Salt Lake City Utah, at over 4,000 feet of elevation in the middle of the dusty desert when the temperature was over 95 degrees. I came in halfway through my Qualifying session, and the bike was right on that temperature limit again. We were only planning on changing the rear tire but we were surprised to see that inside of my belly pan had water sloshing around. 

That ended my session. 

I had no chance to do a quicker time and my starting position was set, without me ever doing another lap. 

The water ended up bubbling inside the radiator which then released the pressure through the stock 1.1 Bar radiator cap, water overflowed the catch can, and then spilled into the belly pan. Thankfully, the belly pan kept it contained, or the water could’ve spilled out, coated the rear tire and I might’ve had a massive crash.

We were sitting in our pit after the session, dejected, not knowing what we could do to keep from boiling besides crossing our fingers and toes. Then a friend stopped by and went out of his way and gave us a special radiator cap to help keep the pressure from burping and sending coolant onto your tire if you hit a bump. 

A higher pressure radiator cap helps keep the radiator at a higher pressure which then keeps the boiling point of the coolant at a higher temperature. They sell them from 1.6 Bar to 2.1 Bar. We personally use a 1.8 Bar cap. A higher boiling point can save you when the starter keeps you on the grid when someone stalls their bike, or you’re racing at an elevation where the bike can’t cool down as quickly since there is lower air density. 

Where do you find a 1.8 bar radiator cap?  You can purchase an aftermarket radiator cap through Cycle Gear’s website. Also, a KX 65 dirt bike will run a 1.8 Bar cap, so you can order one through your local Kawasaki Dealer.


Bar Boiling Points

Sea Level/1 Bar – 212 degrees Fahrenheit – 100 degrees Celsius

STOCK 1.1 Bar – 215 degrees Fahrenheit – 102 degrees Celsius 

1.8 Bar – 244 degrees Fahrenheit – 117 degrees Celsius

2.1 Bar – 252 Degrees Fahrenheit – 122 degrees Celsius