Something to be aware of is if your cooling system froze you may have an internal leak as well, if that's the case you will have coolant in your engine oil causing your oil level to be high and discolored as well (possibly milky looking if the engine has been cranked over or run). This can turn dangerous to your engine if you run the engine because even though it may seem like it's running OK the crankcase can fill up with coolant and over heat the engine from the cooling system getting low, cause a reduction or loss of lubricity to your bearings / cylinder walls / cam lobes / etc, or if enough coolant gets into the crankcase the pistons could start hitting the fluid in the crankcase and possibly cause a catastrophic failure.
There's a tool called a 'cooling system pressure tester' which has a small hand held manual bicycle type pump with a built in pressure gauge that's connected by a hose to a radiator cap type of connector that you lock onto your radiator, once connected you build up pressure in the cooling system by using the pump and watching to see if the pressure stays in the system. If the leak is substantial you could always use compressed air (thru a regulator that allows you to reduce the air pressure down to whatever your radiator cap pressure is rated for) to supply a constant source of air, this way you can try and identify where the leak(s) are at in your engine thru listening and using your hand to feel for leaking air if external. Be cautious if you do this though because too much air pressure (much beyond your radiator cap pressure) could potentially cause damage to your cooling system including blowing out the radiator, hoses, and or gaskets.
