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Discussion Starter #1
So as we are in quarantine I decided to do an oil and filter change on saturday. Every 2 or 3 days I start the bike let it iddle until it goes up to normal operating temperature (temp gauge reading in the middle).
Yesterday I was waiting for the bike to warm up and I saw a small leak coming from below the thermostat. Just some drops. And then it stopped.
Could this be normal as the bike is sitting for like 10 days?
Coolant level is ok
 

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No, it's not normal to leak from the thermostat, or indeed anywhere from the cooling system.
A common leak though is from the weep hole under the mechanical seal, but then it doesn't usually leak on startup and stop once warm.
 

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Are you sure that it was coolant? Could it have been condensation? By the way it is not a great idea to let the bike warm up by idling, so I've heard.
 

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Discussion Starter #4
It was definitely blue as the coolant.
I didn’t know that about warming up at iddle. Since we can’t go out the best I can do is a short trip around the parking lot
It is maybe coming from the hose that goes to the thermostat. It has never leaked before and all seals are new.
 

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Recheck the bypass hose, a leak there might stop after the thermostat opens?
 

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My current '79 leaked a little from the thermostat housing from the day I bought her. I only noticed it after parking, from the intermittent hiss of the drops hitting the hot engine. I ignored it for years, until the moisture rotted out the fan cowl behind the radiator.

I tracked the leak to the right-hand coolant tube, running from the housing to the cylinder head. It was a relatively simple matter to pull the tube, clean the mating surfaces, and replace the o-ring. I followed it up with some high-temp silicone sealant just to be sure.
 

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Starting an engine and letting it warm up at idle does the engine no good and mostly wastes fuel. The only purpose it might serve is to keep the fuel in the carbs fresh. You would be far better off to turn the petcock to Off, drain the carbs and leave the bike alone until you are allowed to use it again (in more northern parts of the world we commonly store bikes like this during the winter).

Also, in order to charge the battery the engine needs to turn at something like 2500 RPM or faster so not only are you using up some of the battery's charge by running the starter motor but you are continuing to discharge it while the engine idles so if you continue doing that you will eventually find that there isn't enough left to start it. Letting a battery sit for even a few hours in a partially discharged state can cause it to lose some of its ability to hold a charge so I would connect the battery to a charger overnight before storing it for the duration. And if the restrictions continue longer than expected start charging the battery every 4 weeks unless you have it connected to a battery maintainer of some sort.

I understand that you want to find & fix the leak before storing the bike. I would start by cleaning the thermostat housing and everything around it really well (this time of forced inactivity could be a good opportunity to take the fuel tank off to clean under it), then start it and warm it up with the engine running fast enough to charge the battery (if possible leave the tank off for this and run it from a hanging auxiliary tank so that you can see the thermostat housing better). Shut it off as soon as you see the leak starting, let it cool down (overnight is best), fix the leak and then run the engine one more time to make sure you fixed the right thing before draining the carbs for storage.
 
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