Thermostat Stuck??

[SAE30]

On my s50 swap the water temp gauge goes to half on idle but drops to quarter when driving, on a winter morning the gauge drops between quarter and the blue block....
i did not renew the thermostat with the swap so im guessing its stuck open, any suggestions on how i would know the thermostat is not faulty or is faulty?
what temperature is the standard s50 euro thermostat?

[Rav335uk]

That sounds ok to me, as you stated, Winter time mine stays about the same.

[SAE30]

That sounds ok to me, as you stated, Winter time mine stays about the same.

Thanks for the input ...

we dont have such hectic winters that u guys have so thats why im worried

[Rav335uk]

Just seen your location, for peace of mind, change it, it's only a few pounds

[SAE30]

Just seen your location, for peace of mind, change it, it's only a few pounds

thanks, gonna have it changed but over here the thermostat is very very expensive