Can anyone explain why my engine temperature, which normally sits between 95 - 100 degrees centigrade, stays at a constant 95 when I turn my air conditioning on? This is very noticeable in bumper to bumper traffic when the ambient temperature outside is high. I would have thought turning the A/C on would put the motor under more strain and further raise the engine temperature?

 

In most cars, turning on the air conditioner puts the fans in the maximum cooling mode at all times to account for the additional heat load the condenser will place on the cooling system. This is not necessarily the case, even in hot weather, with the A/C off. There are most likely a range of temperatures that will cause the fans to kick on in successively higher speeds, until a maximum cooling is achieved at some temperature a good bit above thermostat setting.

 

Correct. Also, the fan settings are adjustable through the ECU.

 

I have read a thread where an owner had his fan thermostat adjusted to switch on 10 degrees celsius lower than the standard setting so I know it can be done, but surely it can't be good for the motor? Having said that, where I live in South Africa the altitude is 1800m above sea level and summer ambient temperatures can reach close to 40 degrees (104 deg F), so my engine runs hot all the time, and that is also not so great for my motor. Would it be worth looking at a bigger custom radiator or adjusting fan thermostat via ECU or any other recommendations?

 

I don't think that condition is bad for the motor at all. In fact, in terms of fuel efficiency some tests show that running the engine hotter allows it to be a little better. The car's cooling system should be able to handle extreme temperatures (and 104f is not what I would consider extreme - that's normal summer weather here!). You could certainly look at ECU tuning down the max temperature fan turn on, but I doubt you would be looking at a serious change in temperature without additional items (such as lower temperature thermostat). A bigger radiator is probably completely unnecessary as well.