What business does an overflow reservoir and thermostat have on your motorcycle? Did you ever wondered what that empty plastic bottle is? The one that's hanging off the chassis of your motorcycle, looking suspiciously like a windscreen-wiper bottle in your car. It's a reservoir designed to collect and re-supply your cooling system with coolant as your motorcycle heats up and starts to boil. It works in conjunction with a thermostat inside your cooling system and is basically a back-up device for an engine that is subject to fluctuating running temperatures.
Should your motorcycle have one? And can you remove it if it does have one? The answer for the first question is, no not all motorcycles have a overflow reservoir, and to answer the second question you better not mess with the cooling system of your motorcycle in a tropical country like Thailand. Anyway we like to give you a little insight into how the system works and how it benefits your motorcycle.
First we look at the thermostat. This little device is a self-actuating valve that opens or closes in relation to its surrounding temperature. In this case, the thermostat is the closed position will act as a detour for coolant-flow, and basically bypasses fluid from the radiator, depending on the design of the system. In doing this, the coolant is only circulating over the cylinder/head of the engine, which allows the engine to reach its optimal running temperature at a faster rate. As the coolant heats up, the thermostat gradually opens and begins purging some of that hot coolant through the radiator. The thermostat is calibrated to keep the engine running at an optimal temperature, so it will meter coolant-flow according to the load on the engine, atmospheric temperature and airflow through the radiator. It also works in reverse as the temperature drops.
Should you ride into a cold season blizzard while traveling the remote region of Chiang Rai and the engine begins to run cold, the thermostat will close off coolant-flow to the radiators and isolate the flow to the cylinder/head only.
By removing the thermostat and overflow reservoir, you reduce your engine's cooling system, which is never a smart idea. By removing removing the thermostat/reservoir system, you are limiting the motorcycle's optimal operating temperature range to a higher power output, as well as increasing your responsibility to check coolant levels throughout the duration of your ride. The motorcycle will no longer manage its coolant level when idling at traffic lights, nor will it reach operating temperature when idling down the road at 90km/h with the cool sea breeze whistling through its radiators.