Sigma Coolant Temperature - What is too Low?

[TheArchitect]

Cruising on the motorway I've noticed the coolant temperature seems to be sitting below the 80deg mark probably at high 60 - low 70degC. Thinking this may be a little low, I don't have an oil temp gauge etc so not able to keep an eye on that separately.

Too low or are they all like that?

2007 SV 1.6 Roadsport 140

[PlastererPete]

This thread might be worth a read:-

https://www.caterhamlotus7.club/forum/techtalk/temperature-drops-when-revved-sigma-supersport-140

[Jonathan Kay]

https://www.caterhamlotus7.club/forum/techtalk/temperature-drops-when-revved-sigma-supersport-140

Good advice.

Please let me know if you'd like a copy of the wiring diagram.

Jonathan

[W33SVN]

Since fixing mine, it does still very occasionally drop to low to mid 70s, but very quickly returns to 80ish again. 
 

I really don't know what else I can do, or whether I should even try, this might just be a trait of some Sigma engines. A number of thermostats in, complete coolant flush (twice) as I lost everything when I changed the last thermostat, new temp sender, checked water pump, pulleys and aux belt (fine), check for leaks (none), bled and re-bled system. 
 

I did have an issue with thermostats sticking from what I believe was radiator sealant in my system to start with, but my symptoms greatly reduced after the above noted work. 

[ScottR400D]

The occasional drop to low to mid 70s, assuming it's on winding up again after a spell of easy cruising, isn't uncommon and shouldn't be an issue. As said, it should recover to 80 after a short while. 

If it's staying in the 70s on a steady cruise it would, IMO, indicate a stat issue.