45 as in farrenheit? so about 7 degrees celsius? not too bad
(i like the cold)
i'm in brisbane (east coast) and in the middle of winter most of the time you get an average minimum of 8 degrees or so.. with day time temps in the low-mid 20's.
in summer here its very humid and most days are high 20s up to 40 degrees celsius. minimum overnight temps in the summer are probably around 18-20 degrees.
i used to live in melbourne and first day i was there it was around 20 degrees with a really chilly wind, and the next morning it was -1 lol.. i love melbourne's weather.. low single figure temps over night in winter, to around 15 degrees in the day from memory.. summer is much the same as brisbane, but its not humid, its really dry. highest temp i've experienced was in melbourne, 46 degrees and by midnight it had dropped to 43!! from memory though, average temps are low to mid 20's in summer.
the most obvious way it affects the cars is with cooling. you really need adequate cooling to keep engine temperatures under control. a lot of cars that were imported in the early days failed miserably here because their radiators were too small and overall couldnt cope at all and engines were seriously damaged.