How to Find Leaks in Your Vehicle's Cooling System

By Deanna Sclar from Auto Repair For Dummies, 2nd Edition

In addition to keeping the water and coolant level where it needs to be, you can prevent trouble in your car's cooling system by keeping an eye out for leaks and replacing old or damaged hoses. The common trouble spots in the cooling system — the places where you should check for coolant leaks— are shown here.

Check for cooling system leaks and other problems.

Look under your vehicle: Look under your vehicle in the morning to see if there’s any liquid on the ground below the under-the-hood area. If you see liquid, stick your finger in it and smell it. If it’s coolant (green, red, blue, orange, or rust-colored), get a flashlight, look around under the hood at the parts of the car located over the puddle, and feel around for wetness. Be sure to check the hoses leading to the coolant recovery reservoir and the radiator.
Check the radiator: Feel the underside of the radiator to see if it’s leaking, and look around your radiator for whitish deposits or rust-colored stains. These indicate old leaks that have dried, but they may not be all that old; water tends to evaporate quickly on a hot radiator. Also check the front end of the radiator to see whether the surface is befouled with dirt, leaves, and bugs. If so, wash them off with a brush and a garden hose.
Check the pressure cap: If your vehicle overheats easily, the cheapest remedy is to buy a new safety cap — or ask a mechanic to pressure-test your cap to see if it’s functioning properly. If you need a new one, give the salesperson the make, model, and year of your vehicle and check the pressure limits (psi) on the new cap against your owner’s manual to make sure you get the right one.
Check the hoses: Regularly check all the hoses under the hood of your vehicle, whether you’ve been having trouble or not. For instant panic, there’s nothing like having a hose burst while you’re driving. If it’s a radiator hose, the resulting shower of steam is frightening at best and dangerous at worst. If a vacuum hose goes, the sudden loss of vacuum can stop your vehicle in the midst of traffic. Checking your hoses and replacing the funky ones before they leak can save your nerves and your pocketbook in the long run.

If you find a hose that’s soft and squishy, bulging, hard or brittle, cracked, leaking, or marked with a whitish deposit where stuff has leaked and dried, replace it immediately before it breaks.

If you find a hose that’s collapsed when the engine is cold but springs back when you remove the pressure cap, the cap or coolant recovery system — not the hose — is at fault.

If your car starts to overheat and you suspect that the bottom radiator hose is collapsing, park in a safe place away from traffic. Make sure that the car is in Park or Neutral with the parking brake on. Then open the hood without shutting off the engine. Take a look at the bottom hose (be careful not to get your hair or clothing caught in the fan or the accessory belt) and see whether the hose has collapsed. If it has collapsed and you have a spare hose with you, replace it.