Fault codes P2181 and P3081

[montygraphics]

I am struggling with fault codes above on my 2005 997.1 3.6L Tiptronic. If anyone can help me I would be so grateful. I know DeMort has dealt with these issues.

P 2181 Cooling Performance
P3081 Coolant Temperature Implausible

After about 15 minutes running the red ! comes on dash with a "Failure Indicator" and the coolant sign and the red warning flashing once per second in the coolant gauge.
The first time this happened a week ago I cleared the codes and it drove fine and all back to normal. Drove it today and up come the same faults. The water temperature is very slow to rise and gets to 50C and drops back to the starting position (40C). The oil temperature does not rise at all.
The instant the codes are cleared the water temperature gauge flicks to 80C and the oil temp gauge becomes normal.

My research leads me suspect a faulty valve on the tiptronic gearbox that controls the engine coolant entering the gearbox heat exchanger.

My problem is that it could also possibly be temp sensors/thermostat or other problems.

I can't see any coolant leaks and the coolant level is spot on.

I also can't understand why the instant I clear the codes the gauges return to normal.

Any help will be gratefully received. Thanks

 

[911UK]

step one is to replace the temp sensors/thermostat, which might have a fault

 

[montygraphics]

Yes I’ll do that first. Thanks.