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Water leaking from overflow on CB500


caretaker
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Hi, I wonder if anyone can tell me what may be the cause of water coming from the overflow of my cooling system.


The history is I have had this bike about 6months but unable to ride it has I have not passed my mod 2 yet. I have started it every week and run the engine and warmed it up to keep the battery charged.Its also had a couple of trips out to the garage for fuel and air in tyres. about 20 miles thats all and all this has been without any problems. Last time I went to run it it started okay as usual and I ran it for a while 10 mins- I then noticed hot water coming out of the overfow pipe. The temp gauge was on medium. Could this be purely down to the fact that I didnt have airflow through the radiator grill or is it likely that i have a sticking thermostat or some other problem..any ideas

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My first guess is there is too much coolant in the system, and the leak you are describing is coming form the expansion tank...


But that is my first guess from your description. My Tiger did the same for a little while, till I realised I kept putting too much water in it :shock:

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My first guess is there is too much coolant in the system, and the leak you are describing is coming form the expansion tank...


But that is my first guess from your description. My Tiger did the same for a little while, till I realised I kept putting too much water in it :shock:

 


Thanks for your thoughts Dan. It would be good if thats all it was. I have never filled/topped the water up whilst I have had it. Not having the chance to take it for a run I can't test it as I would like. Maybe the best thing now is to run the engine as it is and see if it holds temp on the temp gauge.


Do you know if any of these water cooled bikes have a tendency to overheat if airflow isnt going through the grill ? ie stationary for a while with the engine running?and do you know if the water flow is controlled by a thermostat as in a car?

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yes it will use a thermostat but does the rad have a fan on it as some of the cmaller cc bikes tend to rely on airflow through rad to keep them cool and if it is fitted with a fan is it cutting in when bike is getting hot???

 

As far as i know there isnt a fan fitted on the bike. Also I'm not sure if the purpose of the water cooling system is to cool the oil only ie heat exchange or directly via the engine/head itself

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Have pm'd you a link for a workshop manual download.


And yes cooling systems do use a thermostat. (well at least mine does lol )

 


Thanks again for that Dan i'll have a look at it

 


I tried a couple of times but it always provided the italian version for some reason....Mama Mia!

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located under the right hand side panel there is a fuse box, There is a ten amp fuse which is for the fan, check this it is probably your problem, Had the same problem with the wifes CB500S. - Hope it works ;)

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located under the right hand side panel there is a fuse box, There is a ten amp fuse which is for the fan, check this it is probably your problem, Had the same problem with the wifes CB500S. - Hope it works ;)

 


Thanks for that- I located the fuse and checked it/replaced it just in case. I have also located the fan and it spins freely when i spin it so its not seized. I then topped up the water ran the bike and the temp got to past Medium and heading to the red without the fan coming on. I assume now there must be a temp sensor/switch somewhere that could be failty or the fan motor itself has had it. If i can locate the switch it might be worth bypassing it- to test the fan motor


Have you any idea where the 'fan temp sensor switch' would be located?

I have tried downloading a couple of pdf manuals as reccomended but my pc isnt too keen and it locked me up a couple of times..so may need to get haynes manual :roll:

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the sensor will either be in the rad with 2 wires coming out of it or could even be on the thermostat housing along with temp gauge

 



Yes, your spot on- I've just got some more details online and apparently its on left side of the rad. Well thats my 'job to do' for tomorrow sorted out..and keep my fingers crossed its not the fan motor itself as that looks a little more involved



Thank your for your advice

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Just to give a little feedback to those that kindly helped-

Well I've now had chance to look a little closer and removed L Hand rad cover and located the fan switch or more precisely the thermostatic fan switch. (it has one wire from it which switches to earth within the switch and when it does so at the apropriate temp the fan starts.)


My aim was to check the fan motor okay by proving the switch faullty

so I removed the wire connected to the switch and bypassed the switch to earth and the fan runs okay when I turn the ignition on.

so I'm now assuming the switch faulty and not switching to earth/neutral when it reaches the required temp .... and the fan to be okay- next job get a switch!


only a little switch but they seem to be about £35.00 (ouch)

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either a new genuine switch or run a temp one off a switch mounted to handlebars that you can turn on and off as needed all you need to do is connect one side to existing wire and put link to earth in from other side of switch sorted

 


yes, good point it'd work okay like that for sure...and good to remember for an out of the way roadside repair too- but to allow room for me 'forgetting to look at my temp gauge every now and then' I think I'll go for the genuine one..don't want to risk damage from overheating the engine because I'd been daft and forgot about it..... Now that would make me choke and overheat!

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the sensor will either be in the rad with 2 wires coming out of it or could even be on the thermostat housing along with temp gauge

 

I've located and checked and changed the thermosatic fan switch but i still have the same problem of it overheating and spitting out the overheated water from the overflow. Apparently this switch doesnt actually control the temp and the fan only operates in extreme conditions



really now i need to check , thermostat in its housing, Reservoir pressure cap itself?

and maybe even water pump itself if al else fails


I've also had a look at a pdf of the haynes manual and it says there is a thermostat in a thermostat housing and this is located under the tank...anyone done this job? Is it a big job removing the tank to check and remove this thermostat

Same with the Reservoir pressure cap?

It also says there is a water pump which is driven by the oil pump so that could get really complicated!

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its very rare for the water pump itself to fail as it is just a shaft with a blade on it what tends to fail is the mechanical seal that seals the water pump from the oil removing the tank is not a big job remove seat there will be one or 2 bolts holding tank down remove them and lift tank gently from the rear you will need to remove the fuel pipes so make sure fuel tap is in the OFF position unless its a vacuum tap remove the fuel pipes you might need to grip gently witih pliers and turn the pipe to break the seal.once you have removed pipe(s) lift tank and pull towards rear of the bike then lift it off.if bike has fuel gauge you will also need to unplug connector on that

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its very rare for the water pump itself to fail as it is just a shaft with a blade on it what tends to fail is the mechanical seal that seals the water pump from the oil removing the tank is not a big job remove seat there will be one or 2 bolts holding tank down remove them and lift tank gently from the rear you will need to remove the fuel pipes so make sure fuel tap is in the OFF position unless its a vacuum tap remove the fuel pipes you might need to grip gently witih pliers and turn the pipe to break the seal.once you have removed pipe(s) lift tank and pull towards rear of the bike then lift it off.if bike has fuel gauge you will also need to unplug connector on that

 


Thank you again for that.... sounds like removing the tank is worth a try then and see what i can see

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Well todays job ........remove fuel tank to get access to radiator Thermostat


First time I have done it but it went okay and al went straight forward- so I managed to remove thermostat from its housing. Incidently its a good time to check or change spark plugs on cb500

I took it (Thermostat not bike) indoors and emersed it in hot water and it didnt open.....just to be sure i then put it in a pan and heated it up more and it did open..so now not sure if its good or not...but it did open on simmer.. :) ...and before on the bike I had hot water and steam coming from overflow)


Anyway I have put it all back together..... I did notice that the thermostat can fit in its housing in 2 positions (180deg oposite ) and it does make a difference to its position in the housing....so possibly also effect water flow- anyone had experience of this.....?

up to now it seems it could have been a possible air lock in water circuit..but not sure at all

Anyway I have ran the bike and seems okay at the mo but I won't know really know until I take it for a good run (but not allowed yet) so this could be ongoing

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did you have it running for as long as you normally did when it was blowing the hot water out

 


No not really quite as long .....i will need another go at that tomorrow maybe...didnt want to annoy the neighbours :D



Someone on another forum did say it could be a head gasket gone pressurizing the water system so its still inconclusive yet..so I will run it again longer next time

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I had the same problem on an early R1 ,did most of the checks you,re doing, when the temp.got to about 80 degrees water came out of the overflow pipe,..the problem was the Rad cap,I replaced it and problem solved,...hope this helps :cheers:

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I had the same problem on an early R1 ,did most of the checks you,re doing, when the temp.got to about 80 degrees water came out of the overflow pipe,..the problem was the Rad cap,I replaced it and problem solved,...hope this helps :cheers:

 


Yes, it does help and I'll certainly bear that in mind.I'll be running it tomorow to check it again. so if it 'boils' again any possible causes will be handy to know. :salute:

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I had the same problem on an early R1 ,did most of the checks you,re doing, when the temp.got to about 80 degrees water came out of the overflow pipe,..the problem was the Rad cap,I replaced it and problem solved,...hope this helps :cheers:

 


Yes, it does help and I'll certainly bear that in mind.I'll be running it tomorow to check it again. so if it 'boils' again any possible causes will be handy to know. :salute:

 



well tried it again.ran it for about 10/15 min....and it boiled again :scratch:

so I think i try leaving the thermostat out next time and follow that by fitting a new radiator cap !

I think i'm going to get to know my way around this bike engine... :)

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