Heating up in Baleno 2003

[usmanj]

My Baleno JXR 2003 gets heated up after running for about 45 mins in CITY, the temp rises to a threshhold little lesser than than the top most line on the guage. However it automatically receeds within 1 min whenever I make a stop over a traffic light or otherwise.
There is NO Problem with the radiator cap, fan or head gaskit. The coolent is also upto the level. Can someone guide me to resolve this problem. Thanks.

[usmanj]

Just to add for further information, Im running the vehicle on CNG and there is no heating problem during long drives. The engine is in perfect condition.

[SpeedDemon]

Check for faulty thermostat valve or temp guage.

Cheers

[robin]

how about spark plugs heat range, brake system, and A/F mix. setting.