IF you got a car from the 60's or 70's. You could run a straight 20,30,40 motor oil in the hot summer without a problem. The oil will help keep your engine cooler in the summer. Also go down to a 165 thermostat. A trick you can also do is get an old thermostat & punch out the plunger of it. You'll run an open system & still have the proper back pressure in your cooling system. Many people don't realize how important the fan cowl really is. If you don't have one on you should. That piece of plastic can be very important for cooling off the engine. Do you have a flex fan or a clutch fan? Your fan clutch can be bad if you have that. Or you can have the wrong flex fan. Or is it an electric fan? Yes I posted many things here but it's sort of a general question. So I tried to address as many as I can. As for the best way to cool it off when running hot. Time is your best answer. I wouldn't put cold water in a hot engine. Blocks & heads are known to crack that way...