there is other options, i have been hunting and found these
http://trailtech.net/tto_temperature.html
the beauty of these they are small enough to be mounted to either the handle bar or on top of the triple clamp near the ignition switch, you want the 22mm one for the ninja.
have been reading about this gauge. it is battery powered & runs constantly. ( i have found out the battery will last for 5 years & its is waterproof as well!!))
(i have been in touch with these guys via email. the battery is non replaceable & the unit is sealed with epoxy to make it waterproof & vibration proof. the battery can not be replaced.also the unit does not have an on/off switch, it is permanently turned on till it goes flat.you can buy the LCD on its own, you need to email the sales department, price is $24.95 current @ 24-7-2013, this price may change in the future)
( i went hunting for someway to hold the temp gauge to the bike and i found this - ebay - 350844445140 its a water bottle holder and will work nicely. i also emailed the guys who make the lcd and they gave me this link
http://www.trailtech.net/72-PK02.html
have found this, ebay item - 300924703706
it has a 10mm sensor, just need to find some kind of adaptor for it to make it fit a 22mm radiator hose. the beauty of this is that it powered by the bike & can be wired up so it comes on when the ignition is turned on
looks like "acewell" make a 22mm radiator hose adaptor with a 10mm hole in it for a sensor. so this might just do the trick to make the "ebay 300924703706" work with the ninja 300. the acewell 22mm adaptor on ebay is searchable on 261075180611
or
you could go all out and get this baby instead
get it from these guys in the U.K
http://www.translogicuk.com/micro-dash.php
or you can get a daytona water temp gauge
get it here -
http://www.moto-fab.com/motorcycle-...motorcycle-parts/daytona-water-temp-gauge/daytona-water-temp-gauge/prod_38.html
some instructions on how to fit to a 250R (should be very similar to the 300)
http://www.ninjette.org/wiki/DIY_Daytona_Water_Temp_Gauge