JonVFR Posted February 16, 2018 Share Posted February 16, 2018 So a couple of months ago during the coldest months of winter I did a drain and refill on my coolant and bled it per the service manual instructions. I had only ridden the bike a handful of times the following months when it was in the 40s and 50s so they were shorter rides and the bike's running temp didn't really get above 180 degrees. We finally got a warm day yesterday so I rode to work only to have it spilling coolant out of the overflow by the time I got there and parked with the bike's temp touching 230. I thought maybe I just overfilled the coolant and it was getting rid of the excess. I rode it home with temps in the 210's-220's the whole way. It didn't lose any more coolant but after parking in my garage and turning it off I could hear the coolant either boiling or bubbling quite loudly. I haven't pulled the fairings off yet but the coolant reservoir looked empty just from shining a flashlight at it. After doing a little searching, I think the coolant boiling could be due to air pockets so I'm going to try bleeding it again. The fan was on so I know it's working properly. I think the t-stat should be working properly as the bike probably would have overheated otherwise, right? Should I try replacing the radiator cap? Link to comment Share on other sites More sharing options...
Member Contributer ducnut Posted February 16, 2018 Member Contributer Share Posted February 16, 2018 If you weren’t having issues before the coolant change and that’s the only thing you did, you have a pocket of air. When you have the bike to temp, you need to have someone help you lean the bike side-to-side, while having the cap cracked opened. The thermostat will need to be cycling to help the air move through the system, which is why you need the bike up to temp and running. Link to comment Share on other sites More sharing options...
GreginDenver Posted February 16, 2018 Share Posted February 16, 2018 Based on my experience with the 5th Gen I'm surprised that you could be having problems with "air pockets". I have purchased and refurbished two 5th Gens in the last year and a half (bought my '99 in October 2016 and my '01 in October 2017). As I mentioned I did a thorough refurbishment on both of these bikes and I remember being pleasantly surprised at how easy it was to completely refill the coolant. I barely even had to "top off" the system on either of the two bikes after the first run of the engine up to full operating temperature (when the thermostat opened for the first time after the coolant change). Your problem (or at least one of the contributing factors) sounds like a failed or failing radiator cap (not sealing properly so the cooling system can't run at its normal pressure). That's what's causing all of your venting and bubbling and boiling problems, and it also contributes to running hot. Link to comment Share on other sites More sharing options...
daved Posted February 16, 2018 Share Posted February 16, 2018 Another option maybe the rad cap either not screwed down fully or failing to hold pressure. I assume the rads are getting hot? otherwise maybe the thermostat has failed/stuck closed - although they normally seem to fail open Link to comment Share on other sites More sharing options...
JonVFR Posted February 17, 2018 Author Share Posted February 17, 2018 7 hours ago, daved said: Another option maybe the rad cap either not screwed down fully or failing to hold pressure. Ah I think that was the problem. I just pulled the fairings off to add more coolant and the rad cap wasn't quite turned all of the way tight. I'll run it tomorrow and bleed again to be sure and then see how it is. Link to comment Share on other sites More sharing options...
Member Contributer Terry Posted February 17, 2018 Member Contributer Share Posted February 17, 2018 Definitely sounds most like a non-sealing cap to me; hopefully just not tightened down. Not an expensive thing to replace if needed. Link to comment Share on other sites More sharing options...
Member Contributer Stray Posted February 17, 2018 Member Contributer Share Posted February 17, 2018 If the rad cap is failing you can buy one for an R1. I posted pics of them side-by-side on this forum someplace. Got mine for £5 and works a treat. Link to comment Share on other sites More sharing options...
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