S60 not getting correct coolant reading

[simonbyard]

I have a problem with the ECT sensor on my S60 2001 2litre petrol. Usually, it never reads past half way on the gauge (even though I know the engines getting hotter), and sometimes, when the car is pushed hard, the gauge will suddenly show no reading at all - eventually coming back after car is driving a little kinder for a few minutes. Only once did the gauge seem to work properly, and show a high temperature when it was getting real hot. Could this be caused by having no thermostat? Reason I ask is that I havent long had the car, and was getting suspicious it had no stat for a few reasons.
1. At motorway speeds from cold, the gauge would hardly reach 1/4 way up - in slo traffic, it would reach half way, then when driven faster again at a constant speed, would drop right down.
2. Suspicious amount of sealant sticking out the the thermostat housing join - where it would not be needed if a stat and a properly fitted rubber seal had been fitted.

Sure enough, I popped the stat housing today, and no thermostat inside. Typical!

Anyway, just wanted to see if not having a stat would effect the sensor reading - can't see why it should, as when a normal stat is in place and up to temp, if allows water through anyway without affecting the sensor - but I'm sure I read somewhere that it could.