If a car is using antifreeze, but there is no visible leak, then where is it going?

You might have a head gasket issue and the coolant may be going into your oil. This would be very bad. Of course it might be a small leak as the other answer had.

Are you using water to fill, or 50/50 antifreeze-water mix? Never use straight water and don't use tap water to mix with antifreeze, it contains lots of dissolved minerals. If you refilled the reservoir and not the radiator the first time it overheated, then when the car cools down, it will pull it from the bottle.

Wait until the car engine is cold, then add 50/50 to the radiator. Then also fill the bottle.

If you keep losing quarts of fluid, check your tail pipe when the engine has been running a while and warm. If there is water coming out the tail pipe, you have a warped/cracked head.

Check for leaks again but leave the car running. When the coolant heats up it gets pressurized to 12 psi. Then it will come out the smallest hole. So your car only leaks going down the road. When the car is cool there are no leaks cause there is no pressure

You may have a small leak in one of the hoses so it will only leak out when the cooling system is under pressure.Try the same thing but with the motor at operating temperature ..

sometimes as the water pump gets tired, it starts to leak, water pumps usually have a weep hole on the bottom, and when the bearing gets play beyond specifications, the antifreeze may leak once the car is up to operating temperature, you had the right idea though this time drive the car for 20 minutes or so, and park, if fluid starts leaking directly under what seems to be the front of the motor, this could be the problem. there should be nothing in the motor oil, contaminated motor oil is milky white, and there should not be a lot of white smoke out the tailpipe, these are signs of a head gasket leak. if you cannot figure out where the coolant is from, more than likely a head gasket problem. but the easy stuff we eliminate first, so the water pump or a split hose is my first guess hope this helps

Coolant Loss No Leak

Informative topic, just what I was searching for.

I was wondering much the same thing