Higher Pressure Radiator Cap

8 replies to this topic
  • Ronski

Posted February 20, 2002 - 05:21 PM


I saw that Zip-Ty racing uses a 1.8 bar rad cap from a Kaw,probably a KLR 650.They didn't reply to my request for more info, anyone out there know more?

  • YZ400Court

Posted February 20, 2002 - 05:30 PM


Mine is from a KX-500

  • xrracer36

Posted February 21, 2002 - 07:48 AM


high pressure rad cap? why?
i have a problem with overheating my ride late in harescrambles (so i finally replaced the overflow tank (it's a wr model)) but would like to know if this mod would be worth looking into to help my coolent loss prob. doesn't this kinda trap the water in the head and promote more heat ?(not good for the engine or coolant)i mean, if it is boiling over, doesn't that kinda indicate you need to let ol' blue cool down a little before you do any damage? :)

  • txthumper

Posted February 21, 2002 - 09:05 AM


raising the pressure raises the boiling point :)

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  • Alain

Posted February 21, 2002 - 10:25 PM


What would be the distinctive advantage of doing this ?? Some people use additives in their coolants to actually decrease the operating temperature.... So I`m wondering what`s best... hot or cold.....

  • jamracing

Posted February 21, 2002 - 11:20 AM


I have a KX 250 cap. YZF's piss coolant so often, you need the high pressure cap to keep your fluids during a long enduro.

  • xrracer36

Posted February 22, 2002 - 07:23 AM


i realize the whole "raise the pressure, raise the boiling" issue, but that doesn't answer my question, or disprove my point. do you really want to raise the boiling point. that just raises the temperature at which you're bike must operate before it starts to boil over the rad fluid... i use the boiling over as a giant flashing red warning that you're bike is already hot enough, and you better pull it over and let her cool down for a minute before you do any serious damage.
my view on the subject. more heat is bad... an aditive to lower operating temps is good, but if you are going to raise the temp of the bike before you relize how much heat you are making (indicated by the boil over), then you are pushing you're engine closer and closer to it's point of failure.no? :)

  • vznx1w

Posted February 22, 2002 - 11:02 AM


Obviously, it is preferable to not have the coolant get hot at all. However, if the coolant wasn't getting hot we wouldn't be having this discussion.

If we're running hot, there's a considerable advantage to raising the system pressure to raise the boiling point. When the coolant boils it becomes virtually useless in transfering heat from the engine. At the engines hottest surfaces steam is formed creating pressure pockets that prevent coolant from contacting the metal--preventing thermal conductivity between the metal and the remaining water. In fact, this localized steam can happen even if the coolant isn't yet boiling in the radiator. In other words, the coolant is still below boiling temp, except for the local steam pockets. Raising the boiling point helps prevent the steam pockets from forming.
Also, when you boil with a low pressure cap, you are losing coolant so that even after you stop (on the trail-side) and cool down, you will restart low on coolant and all this bad stuff will become worse.
The higher system pressure reduces these problems. The only real downside is the extra mechanical stress on the radiator, hoses, and gaskets that must maintain a seal against the higher pressure.

  • txthumper

Posted February 22, 2002 - 11:30 AM


we really dont have any choice...either keep a good pressure on the cooling system or boil the coolant out and walk back to camp :)

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