Check out the entire cooling system: radiator, coolant, belts and hoses , cooling fans, heater core and water pump.

1a. The Radiator

First, make sure that the radiator core is in good shape. In areas of the country where roads are salted, the core of the radiator can literally rot away. Even though the radiator may not be leaking now, it will be leaking soon. That means bad overheating. And when your engine isn't cooled properly, it can easily blow a head gasket, or crack or warp a cylinder head. In technical jargon, your engine is going to "melt."

What is the radiator core, and how would you know if it's rotten? The core is the little tubes through which the coolant flows so that it can get cooled by the air flowing past it.

But, it takes some experience to recognize a radiator that's rotten, so we recommend that you ask your mechanic to check it out. He'll look at it and touch it to see how hard it is to get it to crumble. Unfortunately this is a destructive test — if it's rotten it will fall apart. But better it happens in the shop than on the highway, no?

Another common radiator problem is a plugged radiator core. If this happens, you'll notice that your engine is running hot when you're driving at sustained high speeds or, as a strictly hypothetical example, while you're climbing a long hill on a hot summer day with your mother-in-law in the trunk.

A plugged radiator core can be the kiss of death for an engine. How do radiators get plugged? Simple. If you haven't had your cooling system flushed since, say, Gerald Ford was vice president, it's likely that many of the little cooling tubes within the radiator core are clogged with rust. And those cooling channels are mucho importante.

Remember — that's how the radiator cools the engine coolant... by passing the coolant through those channels and blowing cool air across them. So, if your radiator is plugged, it will still work, but not as well. And you'll be most likely to notice the problem when the car is under the greatest load (i.e., when you're halfway up Pike's Peak, with your mother-in-law in the trunk).

The bottom line? If your car ran even a little hot last summer, have your mechanic find the cause of it right now before it's too late. If there's any question about the core, he'll do a "flow test" to see if the right amount of fluid is passing through the tubes.

Main Body of Radiator—the
“Guts” of the Cooling.

1b. Belts ... Hoses

Visually check the hoses and belts related to the cooling system. Squeeze the hoses and look for small cracks in the rubber. Make sure the hoses are tight (grab the hose near the hose clamp and make sure it doesn't rotate), and check to see that the belts have the proper amount of tension. To check the tension, push down on the belt. It should deflect about 1/2 inch. On some cars — mostly older ones — a belt turns the fan. On other cars, the cooling fan is electric. (See COOLING FAN below.)

1c. Coolant ... Thermostat

You should be using antifreeze in your radiator, even in the summer. Why? Because antifreeze contains corrosion inhibitors, and actually has a higher boiling point than water. (Remember your high-school chemistry? When you mix two chemicals together, you end up with a boiling point that's higher than either one of them separately.) Should you change your coolant before the summer hits? Most coolant these days is what's called "lifetime" coolant, which means it's good for 60,000 to 100,000 miles before it needs to be changed. So, check to see when you last had your coolant changed. If it’s close to the recommended interval, go for it before overheating season arrives.

If you haven't had your thermostat replaced and your car is well into middle age, we recommend to our customers that they get a new one when they're having a cooling system repair done. A stuck thermostat is a common cause of engine overheating. Replacing the thermostat is relatively affordable and it could save you a meltdown somewhere between Boise and Laramie.

1d. Water Pump

Water pumps break — and when they do, they usually allow all the coolant to leak out. Luckily, a good mechanic can predict when the pump will die. (He does this by jiggling the pump to see how much "play" there is in the bearings. If it's loosey goosey, replace it. Lots of pumps, by the way, are driven by the timing belt, and are difficult to check in this manner. If your car is in this category, have the water pump replaced when you replace the timing belt.)

1e. Cooling Fan(s)

Most modern cars have an electric cooling fan--and some have more than one. The fan is controlled by a thermostatic switch. That is, the fan comes on when the temperature of the coolant rises to a predetermined temperature. You can check the operation of the fan yourself. It's simple — just turn on your car's AC. Then, open the hood, with the engine running (please, take off your ascot before you do this), and listen for the cooling fan. If the fan isn't running, it's not working. Have it fixed — sometimes the fan has gone south, and other times the problem is the coolant temperature sensor.

There are a few signs to look for, if you think your cooling fan might not be functioning. These include overheating while stuck in traffic, overheating with the AC on, or if your AC won't come on at all. If any of these problems are happening to you, the cooling fan could be a likely culprit!

1f. Heater Core

The heater core is part of the cooling system, because the coolant runs through it. If the heater core leaks, the coolant drains out and you're in deep doo-doo. Your mechanic will put a pressure tester on the cooling system to find all the leaks — including this one.

The small tubes in the heater core can also get plugged with rust, over time. If that happens, you might notice that hot air is no longer available from your climate controls. On some model cars, repair or replacement of the heater core can be expensive. Be ready to pay for a full boat payment!