About 7000KM ago I bought my first car - a Legacy LX '94. The first thing I did was replacing the oil, oil filter, checking fluid levels etc. Every was fine then. Yesterday, however, I did a quick check before making a 500km trip. I first drove to town (5 mins) and then checked the fluids. When I opened the hood the first thing I noticed were two places where steam was coming from the radiator (most left and right to the middle), it was only a little little bit though (like the steam coming from coffee). The first thing I obviously checked was the coolant. The reservoir was all empty and it drank about 1.25L of coolant to come up to the low level again - it kind of surprised me, it was at full 7000KM ago.
I think I've been driving with this low level of coolant for a while because I noticed that the 'characteristic bubbling' I always hear when accelerating was gone for a couple of weeks already and this sound was back when I topped up the coolant. The temperature indicator of the engine however, never reached half way the indicator bar so I don't think the engine has been overheated.
With the bubbling stopping something else began (it's only now that I think of this) namely a much higher RPM during the first minutes of driving. It usually made about 1000RPM when the engine was warming up but lately it was more like 2000 - 2200RPM. I was only last time when it started worrying me - I could drive 50km/h without throttle... It seems that with the bubbling coming back the really high RPM is gone.
Should I be worried about some kind of very small leak? I've checked it and there are no traces of coolant anywhere on the engine. Because it's a new car (well for me at least) I used to park it on a piece of cardboard so see if anything leaks - however, the cardboard doesn't show any traces of leaking.
Thanks a lot for all your help!
P.S. I've just bought a Haynes repair manual so you don't have to make complicated explanations where I can find some part - I can look it all up now