Coolant overflow tank

[Pasta Burner]

The recent post in the “working CLASS” thread reminded me to ask this. The coolant overflow tank is always dry...what’s the deal with that? I put distilled water in it a few times and it always seems to gradually disappear. But even if I don’t fill it the bike never indicates overheating. I didn’t come up with any solid answers when I searched this.

[Bob K.]

It's a closed system, so if your coolant reservoir is running dry, you have a leak in the system somewhere. Check for a cracked reservoir or reservoir cap. Check the water pump weep hole. Check around the twinkie. Check the radiator cap.

 

The reservoir holds a tiny amount compared to the full volume of the cooling system so I imagine you could go for a long time with a slow leak without seeing signs of overheating.

Edited July 26, 2020 by Bob K.

[Prairiehammer]

There is an O-ring on the "drain cock" (bypass valve) that often weeps coolant, dripping coolant into the lower cowling (chin fairing) where it may evaporate without evidence of the leak.

 

[saddlebum]

See if you can get hold of a pressure tester and pressurize the cooling system. Start with a cold engine at room temp and leave it sit for a several hours even overnight if you can. Check the pressure to see if it drops. Also park on a dry spot or slide something under the bike so you can see if there are any drips after awhile. You may have to make an adapter out of an old rad cap for this purpose.

 

Hate to say it but if you cannot see an external leak you may have an internal one, though I do believe they are very rare on these bikes. After you have had pressure on the cooling system for a good spell preferably all day or overnight pumping it up if it is dropping try cracking the oil drain plug to see if any coolant comes out of the crankcase. DO NOT crank the engine over while your are performing these tests as you want the water and oil to separate if in fact there is water in the crankcase. Next if no answers are found here then drop the pressure on the tester and fire up the engine to see if it builds pressure on its own. There will be some build up as the engine warms up but you want to watch for is a drastic build up. You let off some pressure once the engine warms up and watch it again for pressure build up while hot.

 

Also if you have run the bike for a spell Check your oil while and see if it turned milky or has milky streaks in it. sometimes if there is enough coolant in the oil you can smell it.

[Pasta Burner]

Thanks guys. I do have a professional pressure tester, as long as the rad cap isn’t some one off design it should work. Just pulled in from a 75 mile ride in 90* heat so I’ll have to wait, but I did not notice the gauge getting above 3/4 at any point and it was at half majority of the time I looked down. Fan wasn’t even running when I pulled her in the stable. I did fill the coolant tank before I left just to see what happens, forgot to check when I got home, but will do so when I refill my beer. There is an oil leak that I’m 99% sure is from a ****ty overused drain plug washer that I haven’t changed yet, but point is I haven’t noticed any I’ll effects in the oil that drips out.