1. Look at both the lower and upper radiator hoses located at the top and bottom of the radiator on the back side and held by hose clamps. Make sure the hoses are securely clamped to the radiator and aren’t leaking
2. Check under the car, inspect the radiator and look around the engine compartment for telltale signs of a coolant leak: Coolant is usually greenish, slippery and sweet-smelling
3. Inspect water pump for signs of coolant leak it may have bad gasket .
4. Check the radiator cap neck for signs off leak you may need to change your radiator cap
5. Freeze plugs . These are the casting plugs or expansion plugs in the sides of the engine block and/or cylinder head. The flat steel plugs corroded from the inside out, and may develop leaks that are hard to see because of the plug’s location behind the exhaust manifold, engine mount or other engine accessories
6. Inspect Intake Manifold gasket for leak by outside leak or internal leak in outside leake you will see coolant sign around it and if inside you will see in exhaust white smoke
7. Internal engine leak like bad head gasket or cracked head or block make car performance very bad and make white gel or creamy in your oil stick or may see it inside radiator coolant and you open the oil cap and check for this signs also beside blue smoke come from oil cap while engine running to know it is internal engine leak you have to make compression test for each cylinder and measure the reading if tow cylinder have low values that mean the head gasket between them have problems and it must the different between max compression and lower not more than 70%
8. Heater core hoses and the core itself it hard to diagnose and may let you doughty having internal engine problem but there is a solution to test your car