Bit weird, about to leave work and my screen wash was empty, went to top it up and noticed my coolant level in the expansion tank had dropped slightly. It was still above minimum, but this car has never lost a drop of coolant. Drove back, temp bang on, checked it at home and the level had gone back up to what it was before. Checked oil, clean as a whistle.

Could it have been a bit of an airlock? I noticed fan ran on for a short while when I got to work. Stat and sensor were done early Jan so I would have thought level would have stabilised well before now. I'm not too worried, it just seemed a bit odd for the level to drop like that, then returned to normal.

Perfectly normal.

 

If it's cold out and the engine is stone cold, it'll look slightly down. If it's hot out and you've been driving for a long time, then it'll look higher than normal.

 

The coolant obviously just expands and contracts slightly with temperature.

Cheers mate, just thought it looked as though it had fluctuated over a higher range than usual and it got my attention as I've never noticed it move much at all.

Yeah it can take you by surprise sometimes when you glance past it expecting it to be at a certain level!

Mine has done this 2. Twice it's stuck a warning light on to say it's low but goes off after 30secs. Maybe I got a faulty sensor tho?

Probably not faulty it's quite common for them to get gunked up and need a clean. Think you can reach into the tank and give it a little scrape with a flathead.