Given that all other variables that effect corrosion remain the same, the answer should be YES. Typically, for every 18 degrees F increase in temperature, the corrosion rate should double in reaction speed.
Most corrosion mechanisms are galvanic in nature (even if just on material is involved). These relationships are usually exponential with temperature.
The one thing to watch our for in cold conditions is what is happening at the warmest place in the system. If the whole system isn't frozed some locations may still be corrosing activly.
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Rust never sleeps
Neither should your protection
I was wondering if it was better to keep my car outside in very cold weather (0F-20F) when there is ice etc on the bottom, rather than putting it in the garage!
From what you say there would be less corrosion right?
Correct! If you live in a winter climate leaving your car out will slow down the rate of corrosion from road salt. However, exposure to your battery and other devices is not good, this is why most people garage their cars (plus a warm car is better then a cold car with snow or ice on top of it).
When it is zero F outside I don't care about the car, I am more worried about ME.
Many of us have leared the hard way that a heated garage in the north will destroy cars. Gets them warm enough for the slush to melt and then the salt has its way with your bodywork.
An unheated garage is the best compromise. Warmer than out doors and no snow, but not warm enough to encurage corrosion.
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Rust never sleeps
Neither should your protection
If you are going to leave your car outside to prevent corrosion then why not go the extra mile and leave the heater off and the windows down when driving. This will help to keep snow accumulations from icing up on the under carriage.
Even after driving the car for a 1/2 hour the ice was still on TOP of the hood, there is no way anything I did would affect underneath! Yes it's very cold. I guess rust does sleep occasionally.