Troubleshooting Cooling System Leaks

8 of 9 in Series: The Essentials of Checking and Maintaining Your Vehicle's Cooling System

When you find a leak in your engine's cooling system, you must decide whether to handle it yourself or to take it to a professional. The following sections cover the different types of leaks and give you a few pointers to help you decide:

Radiator leaks: If the radiator is leaking badly, go to a reliable radiator shop. If they say it’s cheaper to replace it than to repair it, do so.

At the radiator shop, ask the radiator specialists what they intend to do and request a written estimate before they do the work. If the estimate seems high, call another radiator shop, tell them what needs to be done, and ask for an estimate.
Leaks in the engine-block core plugs: On the sides of some engine blocks are little circular depressions called core plugs or freeze plugs. If you see leaks or rusty streaks leading away from the core plugs on your engine block or signs that leaks from them have dried, and you’ve been losing liquid lately, you may need to have the core plugs replaced. Your best bet is to seek professional help on this one.

Check the core plugs on the sides of the engine block.
Internal leaks: Sometimes a leak right under the cylinder head can be the result of an ill-fitting head gasket or the fact that the bolts that hold the cylinder head on the engine block are too loose or too tight. If you try to tighten these bolts yourself, you may damage the gasket if you don’t have a torque wrench. The best thing to do is to get professional help here. If a mechanic only has to tighten the bolts, the cost should be minimal, whereas replacing the head gasket is much more expensive.

The head gasket lies between the cylinder head and the engine block.

With today’s aluminum cylinder heads, it’s quite possible that your cylinder head may have small cracks that are allowing coolant to leak internally. If this is the case, usually you’ll notice thick, white smoke from the tailpipe and/or engine oil that looks like a mocha milkshake when you inspect the oil dipstick. Also, vehicles with automatic transmissions have a transmission cooler inside the radiator that can leak. When it leaks, coolant mixes with the transmission fluid, making the transmission fluid on the dipstick look like a strawberry milkshake. Both problems require professional help.
Leaky water pump: Often, a water pump that’s about to break down sends out noisy warning signals and then starts to leak before it fails completely. On some overhead cam engines, the water pump is behind the timing cover and is driven by the timing belt, making inspection difficult. Leave those to a professional. If the water pump on your vehicle is visible, you can check your pump by looking around it for leaks or signs of rust or corrosion around the seals.

If the pump is leaking in the front where it rotates with the belt, the pump probably needs to be replaced. If the leak is around the gasket that lies between the water pump and the engine, you may be able to stop it by tightening the bolts that hold the water pump in place. If tightening the bolts doesn’t do the job, then you probably need a new pump.
Locating leaks by pressure-testing the cooling system: If you can’t locate the source of a leak and your vehicle is regularly losing liquid from the cooling system, drive to your service station and ask the attendants to pressure-test your cooling system. The test involves very little time or labor, so a friendly technician may do the test free of charge. While you’re at it, have the technician pressure-test the radiator pressure cap as well.