View Full Version : Overheating Problems - RS250

03-26-2005, 08:30 AM
Hi this is my first thread.

I got a 98 RS250 and ever since I got it - its been running hotter than 65deg.

The previous owner had only done like 3000km in the last 3 years so when I bought it I had all the major oils changed including the coolant.

When I'm on the freeway (constant 100-110km/h) on a cool night it'll stick around 67-69...but even on a cool day on the freeway it'll slowly increase its temp to 72-75deg.

I woulda thought with the amount of air coming in it would be decreasing not increasing. BUt when I change through the gears to a stop the temp will come down to about 68deg.

Anything I should look for and fix??? I guess topping up the coolant more often might help a lil - it heats up pretty quickly from what you other guys have talked about...within a few hundred metres when it hits 35deg it goes straight to 50deg

Appreciate your advice guys!

03-26-2005, 09:15 AM
Is this a 316cc engine? If it is that is "normal" as the stock radiator isn't suffucient for the increased displacement.

03-26-2005, 01:56 PM
Make sure your system is bled. Bleed it at the radiator and the 10mm nut at the water pump. Then top off the radiator.

If you have never done this....open your radiator.....pour fluid in till it tops off. ..crack the 10mm nut at water pump....keep pouring until you see bubbles, than you'll see the fluid flowing.....tighten that , then goto the radiator.....once again 10mm ...open it up and do the same thing.

Top it off....and you should be good to go. Sounds like you have abit of air in your sytem.

If this does not work......tear it down!!! :cathat:

03-26-2005, 04:48 PM
extract of my tips page:

Coolant: Replace every 2 years 50/50 mix of water/coolant suitable for aluminium radiators. Remove the cylinder drain plugs, water pump bleed screw, radiator bleed and fill caps. Start filling as slowly as possible through the radiator fill cap (not expansion bottle) when fluid escapes the cylinder plugs tighten them. Keep filling until it runs out of the water pump casing screw, tighten it. Keep filling until fluid escapes the radiator bleed screw and tighten. Now fill all the way to the top of the filler and secure cap. If you fill very slowly all the air should be pushed out. If you do get air bubbles the bike will likely run too hot. Put some mix in the expansion bottle. Mark the level and run the bike until at operating temperature. Allow the bike to cool and check level.

NOTE CYLINDER DRAIN PLUGS, by slowly I mean a trickle.

03-26-2005, 11:03 PM
:blah: Or you can just fill it.

03-27-2005, 07:35 AM
check your thermostat as this could be no opening up quickly enough.

Also the radiator cap should be changed if it has not been changed.

03-27-2005, 01:14 PM
Typical. Try and help someone. Fed up of this forum.

See ya :spankie:

03-27-2005, 02:22 PM
Could someone describe or photo where the cylinder plugs are? I am changing over to a waterless coolant (EVANS ) and want to be sure I have the system drained and filled properly.


Smoke Eater
03-27-2005, 05:21 PM
I've heard really bad things about the Evans Coolant. Some people have even had their bikes run significantly hotter.

03-27-2005, 06:19 PM
Gee I wish my bike (Honda SP1) ran that cool. Im lucky if it is under 80deg. Still it is pretty warm in Qld Australia. I havnt had the chance to ride my RS250 as it is still getting worked on. I didnt know that they were meant to run so cool. I mean those temps sound fine to me... but I dont know if they are wrong for two strokes.

03-27-2005, 08:29 PM
yep four strokes run heaps hotter!

In melb I cover about 1/3 of the radiator through the year (until summer) to try and get it hot enough. Qld it should run around 65 most of the time, they can over heat in traffic on a hot day very easily as there's no cooling fan. You gotta keep moving!

Pro Backmarker
04-01-2005, 06:08 AM
Problem sounds like an air lock in the cooling system to me....

What no one has mentioned is laying the bike over on either side during the bleeding process. A search should reveal some tips.

04-09-2005, 05:36 AM
my RS250 has a temperature of between 55-65 degree when riding, but in stop/start traffic it goes as high as 82degree C.

Is this normal to have a high temp of 80ish degree C in traffic???

i did the above bleeding of the air etc very carefully as well.

04-10-2005, 11:39 AM
I got stuck in traffic in Stratford on the bank holiday and mine was over ninety without achieving critical core warp tho it can't have been far off! BTW, did you all watch the boy Rossi today? He may be on a Yamaha now but I still remember the Nastro Azzuro days. :worship:

04-11-2005, 01:57 AM
I got stuck in traffic in Stratford on the bank holiday and mine was over ninety without achieving critical core warp tho it can't have been far off!

Had mine for a ride after the winter service and the temp. reatched 120*C, had air in my waterpump. I removed the screw on the pump and filled the pump house up whit water/coolant. Then it worked perfectly.

I think i was on an critical point there!! :eek: