I realise this might sound daft but you would be amazed how accurate a digital cooking thermometer is. Available for a few pounds from most cook shops, carefully remove the header tank cap (slowly if the engine is hot, it's OK to run at idle with the cap off) pop the probe in the header tank coolant or tape it to the top hose for a more accurate reading. I noticed my 08 +4 was only indicating 80 degrees at steady motorway speeds and never went above 90 even in traffic. The digital thermometer has a hold function and after a blast showed the peak temperature was 98.5 degrees and the gauge never went above 80, at idle the fan kicked in at a dash gauge reading of 80 whilst the digital showed 95. I just consider the cars temperature gauge as accurate as the cars fuel gauge and as long as it does not go above 90 I shall ignore it.
