minimum OAT
 

Is there any reason to set minimum operating ground temperature?
A320 FCOM limitations say min temp is-40 at 0 pressure altitude,but some planes have -46 temperature limit.What's wrong with the first planes???Why have they got -40 and other -46????
Thanks.

Different fluid limitations (perhaps brakes?) ?

Globally Challenged

This is probably it. And not different fluids necessarily. System design and maintenance procedures have to start with some number. And then certify the design/procedures. So it could be as simple as the same fluid with different limits set for moisture absorption.

You could go to the manufacturer and request recertification to new limits. But every system will have to be investigated (fuel, lubrication, etc.) at the new numbers. That won't be cheap.

Could be fuel control components. Some seals and o-rings materials used in the fuel system don't work well below -40 and can result in excessive fuel leakage.
There are different seal/o-ring materials that work fine at -40, but wear out much quicker. So the engine companies sometimes give an operator option of the seal/o-ring materials in the fuel control - with different temperature limitations.

737-8 that Conoco flies is good to -50.

Probably the manufacturer only certifies down to a temperature that is required for what they expect sales for.

The ATR-42 had -40°C as its lowest OAT for takeoff(this is what I found on an internet search anyways) but I flew ones that had a lower temperature certified down to -54°C as it was operated in colder conditions. What exactly had to be done to achieve this? I'm not sure but I think our company paid the expenses to certify the lower OAT as they were purchased used.