radiator cap

3 replies to this topic
  • willis7864

Posted April 10, 2002 - 12:23 PM


Can you plesae help,i hear that if you fit a bigger radiator cap this will help the bike run cooler for longer.ie it will not spill out of the over flow,as there is a stronger spring in the cap.So this keeps the coolant in therfor helps the bike run cooler.Can anyone tell me if this is correct.If so what size cap.
willis a 2001 426 owner.

  • PumpkinHumper

Posted April 10, 2002 - 02:26 PM


I was wondering the same thing. I dont think it will make it run cooler. Actually it will run hotter. It just wont boil over as soon. Because the cap has a stronger spring it will stay closed longer before blowing. Mine was boiling over bad a few years ago while ridding some really nasty 1st gear single track in 90 deg heat. I ended up drilling a series of holes in the plasic brush guards over the radiator to try to get more air into the radiators. I also added redline water wetter and a vented front number plate. I havent boiled it over since then. If the problem persisted I was thinking of having the radiators striped of paint. I was told that un painted radiators work better than painted. Somethng about disipating heat better. Boysen also makes a water pump cover/impeller that is supposed to help the temp drop. But the last time i called them they diddn't know what i was tal;king about.

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  • moto_madman

Posted April 10, 2002 - 02:56 PM


its not really a larger radiator cap. It's just a stiffer spring. The rate is listed on the cap. Usually the stock rate is 1.1. You can get a 1.8 from a ktm or a KX80. This will not allow the coolant to boil over as easily. The idea that it runs cooler is somewhat true. If you keep the coolant in the radiator it can keep engin temperature cooler. Radiators can't cool when the coolant is on the ground. Switching to a performance coolant can help boiling over. I use Engin Ice. The modifications that YZMAN400 performed can also help. The vented number plate is mostly to bring more air into the intake and cool the ignition but it looks cool and it cant hurt. Stripping the paint off the radiators will help it release heat better. The paint just acts like a wall holding the heat back. Check your jetting also. If its too lean it can cause the motor to overheat. Sand riding and tight trails can put a lot of load on a motor. Good oils will cut down on friction and friction translates to heat. Factory teams have extra louvers over the radiators to help bring more air through them. They also weld extensions or use larger radiators. More coolant and or surface area can help cooling greatly. I think i covered just about everything. Did i miss anything?

[ April 10, 2002: Message edited by: moto madman ]

  • willis7864

Posted April 11, 2002 - 12:04 PM


Well thanks everyone i will try them. :)

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