Using lower octane is fine for driving as long as the car doesn't ping. I was saying that you need to use 92 octane during the test, because nox can be higher due to a lower grade of fuel, but it won't change it by 1000ppm. Changing the thermostat might be a good idea. If you are confident with the new radiator, then the fan clutch could be the problem. Most fan clutches that are changed did not need to be changed. A viscous style fan clutch needs to feel hot air through the radiator to function properly. Many fan clutches are replaced, because the radiator is restricted, and the fan clutch is blamed. If you have good coolant flow through the radiator, check that the fan clutch is making the fan draw heat from the radiator.

Peter

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