I don't think Holden could give an 'operating temperature' for any of their products. There are too many variables. For example how fast you are travelling, how much weight the vehicle is carrying/towing, the condition of the cooling system and even the proportion of Glycol in the coolant. For example: 55% Glycol at o psi pressure the coolant will boil at 108.5 degrees Celsius. With 55% Glycol at 26.4 psi it will not boil until 142.5 degrees Celsius. With a cooling system what you/they are trying to achieve is the coolant NOT boiling. If it does then the system is incapable of continuing to cool. So what is the optimum operating temperature - NOT BOILING. Hope that helps you to get a slightly clearer picture. The most important aspect in maintaining a healthy cooling system, is use the correct coolant as recommended by Holden, make sure you have the system flushed at least every 4 - 5 years and maintain quality hoses and serpentine belt. Good luck.