Coolant bottle overflow tube

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1st Shirt Maxer

1st Shirt Maxer

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So, I just finished doing a lot of work on an 01 that I purchased last August. The only thing on the cooling system I did was replace all the hoses and drain and refil the entire system. After getting the bike running today I noticed every time it gets warm, coolant starts coming out of the overflow tube that runs down right in front of the rear tire. The temp needle is just below the half way mark and after 15 minutes of idling, never got above the half way mark but it did piss out a lot of coolant. I looks and acts like a stuck thermostat but wanted to verify that on here. Anyone had the same issue and if so, what is the downside to running the bike without the thermostat?
 
Could be a bad radiator cap that won't hold pressure. Or you might have a bad head gasket that is allowing combustion gases into the cooling system. I would start with a new thermostat and radiator cap and see if the problem persists, and if it does you can do some checks for a bad head gasket.
 
I should have asked if it was doing this before you changed hoses and coolant? The thermostat is responsible for maintaining correct operating temperature, so running without it would mean you would have to heat the entire cooling system up before reaching the correct temp.
 
The only way coolant can flow into the bottle is when the radiator cap builds enough pressure to open the relief and open flow. Typically this happens when the temps reach their hottest right after the bike is shut off. The vent opens, coolant comes out, the temps cool down, and the fluid is sucked back in by the vacuum created in the engine during the expansion process. This is why you have a "HOT" and "COLD" setting. If overfilled the engine will try and evacuate the excess that is not designed into the reservoir.

Now, if the proper settings are done (filled right) and it continues to fill up then you either have a bad cap, engine getting excessively hot and causing the fluid to boil (which makes more pressure then designed), or the head gasket is bad allowing combustions pressures in to push more fluid out then normal. Usually a head gasket bad will only do this at pressures above idle (or more then half throttle). BUT, it can go bad in varying degrees too.
 
How common is it for a radiator cap to go bad where instead of the prescribed psi, it functions early with less pressure? I synced the carbs today watching the coolant bottle. It never filled up but all the fluid inside the bottle pissed out of the overflow tube. The level started about half an inch UNDER the full mark and the bike never overheated. I'm baffled...
 
Thanks for all the help as I feel really stupid. After replacing both the radiator cap and thermostat, I finally took some time to go through the whole cooling system and found the simplest solution, I had the coolant bottle overflow tube and the tube to the filler neck reversed...problem solved
 
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