Temp gauge fluctuations and slowly losing coolant... HELP!!!!

[maxamplitude10]

Guys, Ive owned my ED30 for 4 years and completed the same 16 mile trip to work and back most days on the same route. It has 109k on the clock and has been maintained to the highest standards, recently I have noticed my temperature gauge which for my entire 4year ownership has sat at TDC 90° has started to slightly fluctuate down to 80° and back upto 90° on various occasions.
In addition whilst checking the oil recently I noticed the coolant was on the minimum level in header tank. I topped this up to max around 3 weeks ago, on checking again this morning the coolant is down to min level again??
I know people are going to suggest thermostat etc but this does not explain the coolant loss... I'm thinking along the lines of head gasket or head leaking?
Please help!!!
Regards
Maxamplitude

[Joshy]

When my coolant level dropped, it turned out to be a damaged radiator.
May not be your issue here, but worth checking.

[maxamplitude10]

Yeah i'm going to give it a good visual check this afternoon but I haven't noticed any water on floor ot dripping etc?

[lukemk5gti]

I've had more or less the same situation as you.

I replaced inline and main thermostat which fixed the temp gauge so that's not connected.

With regard to the coolant loss:

My girlfriends loss was due to a badly fitted water pump
Mine is due to an o-ring on the rear of the coolant system failing causing a slow weap. To repair will cost €350 in my case so I'd rather top up 100ml coolant a month than pay that.

[maxamplitude10]

Thanks for reply a lot of people are saying thermostat tbh just seems strange that both issues seemed to start at the same time, but like you say may well not be connected....
I'll investigate this further:-)