MilRob

Thanks your quick reply.
The needle doesn't drop as if signal lost.
It drops steadily until reaches C as the revs increase under full throttle over 15 secs or so, and climbs back to normal similarly as soon as I back off.
Which led me to believe thermostat might be problem?
It had new water pump fitted 6 months ago, but not sure about thermostat.
Regards Miles