cold starting is hard on starter to begin with and when it gets down to 15 or under its better to bump starter for a second or two and let it sit for 5 seconds and repeat and do it 5 times or so maybe 10 times if it's below 0 . what that does is the compresin of the engine will heat up things enough to start a little easier with a lot less wear and tear on the starter and engine. shouldn't need starting fluid at all