radiator cap?

從邏輯上如果哪裏漏，應該慢慢漏，不是突然少一公升。而且你提到第一次發生是一下子開了幾百mile之後，我在google上麵看到這樣一個case，也是別人問一樣的問題，下麵有人這樣回答：

The first thought that comes to mind is that the coolant is getting pushed out the reservoir overflow tube when the engine warms up because of a bad radiator cap. A pressure test won't show this, because one has to remove the radiator cap to do the test! You can test a radiattor cap with a thermometer, a hotplate, and a Pyrex vessel. Simply hang the cap into the water, turn the hotplate on, and see what temperature the T-stat opens at.

像你的情況麽？