Your Cadillac Deville radiator is your main line of defense against overheating. As you drive, your engine heat builds up, and if its temperature gets too high, then it could be bad news for your engine. Good thing your radiator is there to ensure proper coolant flow and engine cooling. If this component malfunctions, then you're bound to see that overheat warning light on your dashboard blinking in no time. Keep in mind, though, that overheating can be caused by other components related to the radiator, so be sure to check them as well when diagnosing the root of your problem.
Having low levels of coolant is actually the most common cause of overheating. While your engine is cool, open the radiator cap and see if the radiator has enough fluid in it. If necessary, fill the radiator with a 50/50 mixture of water and coolant.
Make sure to check for any coolant leaking from outside the vehicle. If you notice a sweet smell or a green liquid puddle on the ground, then you might have a leaky radiator or hose. Seal or replace leaking components accordingly.
It's important for you to check your engine temp when you hit highway speeds. If your engine begins to overheat when you hit 55 miles per hour or more, then your coolant or water is not circulating properly. To check if coolant/water is circulating properly, start the engine with the radiator cap off. If the water pops over the top smoothly while still retaining its amount, then you're all good.
Hoses can become brittle or cracked over time, so be sure to check their condition after a while. Also check for leaks in the seams or in the fittings. If you spot damage, have these hoses replaced immediately.
If your thermostat is open and clear, then the water will be able to pass through it. However, if it is clean yet the water isn't circulating, then you might have a leak in the water pump.