Q: Engine oil leak only when temperature goes below 12 degrees F.

Hello, Unfortunately, in extreme cold weather the fluids in your car are not thin enough in their cold state to be forced through internal seals, which can cause them to tear the seals. When this happens, various fluid leaks develop in places where a particular seal may have been a bit weak or on the verge of failing. Where specifically underneath the car the leak is coming from, will determine how to proceed in terms of repairing the leak as there are many different places this may be coming from. I would recommend having a professional from YourMechanic come to your location to take a look at your oil leak and make the necessary repairs.