today I road my bike to work. When I started her up this morning she idled nice and smoth. when the temp rech the low side of normal I hopped on and went to work. My commute is about 30 miles one way.

All the way there the temp gauge only got as warm as the low side of normal. ( I was cruising at about 75 mph). Once I got to work, I idled accross the parking lot to my space. At that point the temp gauge shot up to the high side of normal very quickly. The collant also spilled out on the ground. It was not spilling from the overflow tank, it was comming from the top of the radiator. Other than a week radiator cap, does any one have any ideas on what would cause this problem. I plan to replace the radiator cap even if that isn't the problem because the bike sat for a long time before I got it.

Any help will be appreciated.

ride safe and often
Ron

 

Had the same problem a couple of months ago, i replaced the radiotor cap and pressure valve, also check the tubes,
old age can make them crack at the fittings, and when the pressure valve doesn't open enough, the pressure builds up,
and coolant gets trown out. Low on coolant builds up the temperature FAST.
Flushed the radiator a couple of times, new coolant (make sure to get the right coolant for alu engines),
and it runs as smooth as a (cool) baby again.

 

I've just come back in the house from working on my bike because of something like this. Not only check the hoses, but also check the plastic splitter below the themostat. Honda put the splitter and thermostat at such an angle and only used a straight hose that it puts a lot of strain on the plastic splitter. After 16 years, one of the plastic flanges might have broken off and allowed the hose to slip up slightly allowing a slow leak around the hose clamp.

 

If the bike has been sitting a long time the first thing to do is flush out the coolant. It sounds like it could be a sticky thermostat too.

If you're going to replace your radiator cap and or your thermostat, don't waste your money on the genuine Honda motorcycle crap, just take your old ones down to a good auto parts store with smart people in it and you'll be able to find stuff that'll work just as well for a fraction of the price. At NAPA they have a book with all the dimensions and temperatures of a bunch of their thermostats so you don't need to open up all the boxes.

Genuine Honda Motorcycle thermostat $49.99
NAPA replacement $6.99

I know that someone here found a radiator cap at an auto parts store for much less than

 

From a recent post I belive the radiator cap is from a 90's mitsubishi and the Stant part number is11227 also for $7

 

Thank you for all the replys. I have found what I believe is at least part of the problem.
On my lunch break I went to Oceanside cycle supply and picked up a radiator cap for cheep.
I put it on and filled up the radiator. I was able to get home with the temp staying in the normal range. I picked up the pace on the way home to keep good air on my radiator fins. (85 to 90 mph-we drive that fast on the interstate in southern california) When I slowed for traffic it went up when I got heavy handed it went back down. When I got home the same thing happend, colant spilled on the ground. So after the bike cooled I remove the access panel to take a peek at the radiator cap. there was a hole in the hose just benieth the cap. Now I will replace the hose, pressure valvue and thermostat to go with the new radiator cap. Then I will trouble shoot from there. With all those parts known to be good it will be much easier to find the rest of the problem assuming anything else is also bad. Fortunately the switch that turns on the fan when the temp gets to what ever ( I belive it is controlled by the thermostat) is only about 35 dollars or so I was told. If anyone has any more ideas I am up for hearing them all.
again
thanks

 

Where is this presure valve located. I think I should change it even if it is working right since is most likely is kind of old.

 

The pressure valve is part of the radiator cap.

The fan is operated by an electric thermostat switch located on the left side of the radiator. That's seperate from from the main thermostat, which is a mechanical valve that regulates the flow of coolant to the radiator, it's located in the aluminum housing under the radiator cap.

I think the next thing to check out is your fan switch. See if the fan is on when the temp is high.