Yeah........... don't leave that in the winter though....
poppin' freeze plugs is bad.
especially if its on the rear.... you'll have to pull the motor to replace 'em.
Its that rare chance that it dips below 5*F that you might run into issues.
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you should always use antifreeze, it keeps the block from rusting, (rusty blocks clog radiators) lubes the water pump, and raises the boil temps, and keeps the coolant from freezing. your car will thank you in the long run.