Temp gauge moving

[99auforte]

So, I'm not sure if I am expecting too much of my Falcon or if I have an impending issue.

The past week or so I have noticed the temp rising in my Falcon. The AU Forte has C then a NORMAL section and then there is H

The car has always sat in between th N and O on the gauge, however this has gone up to A last week under full throttle with aircon on Recycle and up a hill. The temps in Adelaide have been high 30s since the first occurence of this.

Temp returns to normal when at top of hill.

Replaced thermostat yesterday and tested on some hills - no sign of issue.

Asked wife today how it was going...she said 1st hill - no problem - which is the biggest of the trip......but second hill - it moved between the R and M and then returned to it's normal position at the top - which is between the N and O.

Temp in Adelaide again was high 30s.

Am I being overly cautious and this is normal for red hot days up hills full throttle with air-con on?

The recent changes to the car since this occurred is Gas system added - and this is whilst using gas (have not tested on petrol). I heard somewhere Gas can cause engine to run hotter???

Car had new heavy duty radiator and full flush in December 2006.