Heater placement

Mr Heater makes several types of heaters. I assume you are talking about the radiant heater. If so, two things to consider. They give off water vapor. They give off poisonous gas, carbon monoxide. Therefore a little ventilation is necessary. Don't make your garage air tight!

This type of heater is popular and works well. Positioning it is important. Radiant heat is directional - and not affected by air movement. Depending on what the work you are planning on doing, you could position the heater to aim at the front of your car(engine bay) or at the work bench.

I have a pellet stove in my garage, but I also have a Mr Heater tank mount radiant heater. The tank mount heater can be moved around to where you want the heat; where you are working.