biggeffory Posted October 17, 2022 Report Share Posted October 17, 2022 Hi, I have a 2004 Scorpa SY250 (with Yamaha TYZ250 engine) and it keeps overheating. It takes a good run to get it to overheat but I know it's overheating because coolant is purged from the radiator cap overflow hose. And more recently it actually blew coolant out of the radiator and created a radiator leak. The fan also runs non stop, once it starts, even if the bike is kept moving. Things I've checked: - It has coolant, engine ice (proper stuff) - The water pump works - The fan comes on (so the fan itself and the thermostat is fine) - The radiator has flow, the coolant can go in the top and out the bottom so there are no blockages So it seems to me that the cooling system itself is fine but the engine is generating more heat than can be cooled; I've no idea why though. This is my first trials bike and I love riding it but currently I have to turn it off every 15 mins to avoid overheating it, which isn't great. Not sure what else to do with it, but would love to sort the issue. Any ideas or suggestions are greatly appreciated 🙂 Thanks Quote Link to comment Share on other sites More sharing options...
lineaway Posted October 17, 2022 Report Share Posted October 17, 2022 Are you riding it like a trials bike or just going fast. Quote Link to comment Share on other sites More sharing options...
biggeffory Posted October 17, 2022 Author Report Share Posted October 17, 2022 (edited) 5 minutes ago, lineaway said: Are you riding it like a trials bike or just going fast. As a trials bike, 100%. I have other bikes for going fast. I usually ride 2nd or 3rd gear sections and hill climbs etc. Nothing out of the ordinary. I also very rarely ever rev it out, as I've no need. So it shouldn't be overheating based on how I ride it. Edited October 17, 2022 by biggeffory Quote Link to comment Share on other sites More sharing options...
tshock250 Posted October 17, 2022 Report Share Posted October 17, 2022 (edited) I'd be looking at the impeller again. Are you sure its not spinning on the shaft or something? Edited October 17, 2022 by tshock250 Quote Link to comment Share on other sites More sharing options...
biggeffory Posted October 17, 2022 Author Report Share Posted October 17, 2022 (edited) 9 minutes ago, tshock250 said: I'd be looking at the impeller again. Are you sure its not spinning on the shaft or something? I will double check it to be sure. What's the best way to test the impeller is pumping the coolant properly? The impellor shouldn't turn on the shaft when I fit it right? Or can there be some movement? Edited October 17, 2022 by biggeffory Quote Link to comment Share on other sites More sharing options...
richt Posted October 17, 2022 Report Share Posted October 17, 2022 The impeller should be solid on the shaft. Even when the engine is stopped the coolant will circulate ("Thermo Syphon") so long as the level is full. The main causes of heat and extra pressure are often due to combustion gasses leaking into the cooling system via a leaking head gasket or a leaking seal in the radiator cap not holding enough pressure so the coolant boils at a lower temp. To test the pump, you could try undoing the top rad hose and kick start the motor or briefly run it whilst holding your thumb over the end. Note it shouldn't be easy to stop the flow, but you are checking for good positive circulation. Hope this helps. Quote Link to comment Share on other sites More sharing options...
biggeffory Posted October 17, 2022 Author Report Share Posted October 17, 2022 28 minutes ago, richt said: The impeller should be solid on the shaft. Even when the engine is stopped the coolant will circulate ("Thermo Syphon") so long as the level is full. The main causes of heat and extra pressure are often due to combustion gasses leaking into the cooling system via a leaking head gasket or a leaking seal in the radiator cap not holding enough pressure so the coolant boils at a lower temp. To test the pump, you could try undoing the top rad hose and kick start the motor or briefly run it whilst holding your thumb over the end. Note it shouldn't be easy to stop the flow, but you are checking for good positive circulation. Hope this helps. OK, will certainly give this a go (undoing the top hose and trying to stop the coolant), to test the pump/impeller. I recently changed the head and base gaskets and torqued them down to spec so that (hopefully) isn't an issue. Thanks for the help! :+1 Quote Link to comment Share on other sites More sharing options...
biggeffory Posted October 17, 2022 Author Report Share Posted October 17, 2022 (edited) Am I right in saying that if the cooling system (all of it's components - pump, fan, rad, thermo etc.) are working correctly, that the engine shouldn't be overheating? Or is there other factors that can cause issues e.g. can the engine be generating too much heat (under normal usage) that the cooling system isn't adequate? Also, the fan shouldn't stay on constantly (once it starts) either? Edited October 17, 2022 by biggeffory Quote Link to comment Share on other sites More sharing options...
richt Posted October 17, 2022 Report Share Posted October 17, 2022 Yes, you are right the cooling system should be adequate and has been for about 18 years😀 so something has happened or changed more recently. I reckon the fan is operating ok it comes on and stays on because it needs to. When the engine is stopped to let it cool the fan isn't running when you start it up later. Your radiator is clear inside and outside then something is generating more heat than normal. Did it do this before changing the gaskets? Quote Link to comment Share on other sites More sharing options...
biggeffory Posted October 17, 2022 Author Report Share Posted October 17, 2022 (edited) 11 minutes ago, richt said: Yes, you are right the cooling system should be adequate and has been for about 18 years😀 so something has happened or changed more recently. I reckon the fan is operating ok it comes on and stays on because it needs to. When the engine is stopped to let it cool the fan isn't running when you start it up later. Your radiator is clear inside and outside then something is generating more heat than normal. Did it do this before changing the gaskets? It has always overheated since I've owned it unfortunately. I took most of the engine apart and replaced what looked damaged but maybe I've missed something. When I start it up and the fan comes on, it never goes off. So I kill the engine and let it cool before running it again. This is currently the only way I can prevent it from overheating. When it has cooled naturally and I start it again, the fan isn't on telling me the thermostat and fan are fine. The Radiator is a little beat up but functional from what I can tell. So I agree with you, it's something else. Edited October 17, 2022 by biggeffory Quote Link to comment Share on other sites More sharing options...
biggeffory Posted October 17, 2022 Author Report Share Posted October 17, 2022 Just checked and the impeller is turning freely on the shaft! Needs a new one I guess? Yamaha charge 62 GBP for a new "impeller assembly" - my god! Any way I can fix rather than replace? Maybe a second hand impeller (not the full assembly) will do the job? Anybody know where I can get one? Quote Link to comment Share on other sites More sharing options...
Cookiemonster Posted October 17, 2022 Report Share Posted October 17, 2022 If you search under Scorpa on a well known internet site there’s a lad on there whose always breaking Scorpas so worth a look Quote Link to comment Share on other sites More sharing options...
Cookiemonster Posted October 17, 2022 Report Share Posted October 17, 2022 There’s a 2008 model on there own quoting all parts available Quote Link to comment Share on other sites More sharing options...
biggeffory Posted October 18, 2022 Author Report Share Posted October 18, 2022 I took a video of the spinning impeller but it's an illegal file type here so the pictures will have to do. The first picture shows the impeller on the shaft and can freely turn - I was able to spin it, zero resistance. Definitely gonna replace it and check for overheating. Will update here when the verdict's in. Thanks to all who've commented so far :+1 Quote Link to comment Share on other sites More sharing options...
richt Posted October 19, 2022 Report Share Posted October 19, 2022 If you can't get a replacement part, I would recommend Loctite 638 retaining compound. Quote Link to comment Share on other sites More sharing options...
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