Q: Cars overheating but engine is cold and the heater blows cold air

Hello...the simplest option is to just request an engine overheating diagnostic and the responding certified mechanic will identify the root cause(s) of the troubles you are writing in about and get the repair estimated for you. Repairs can be commenced right away, too, of course. If the vehicle is overheating, or you have suspicion that it is, continuing to drive it could warp the heads and block. On your own, once the engine has fully cooled, you can check the coolant level. If low, add the appropriate mix of antifreeze and distilled water, and be sure to fill the recovery tank, too. If it is low, you might have a leak and a leak diagnostic would be the appropriate service if you suspect a leak. If an engine "feels" cold, or "normal" but the dash gauge shows overheating, you could have a faulty temperature sensor and/or gauge. No cabin heat could be due to low coolant, blocked passages, faulty heater control valve and/or faulty blend door(s) in the dash ventilation network. Your best bet is to commence with the engine overheating diagnostic and the responding certified mechanic will be able to guide a resolution to all of your concerns from there.