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Auto Repair: Repairing Leaks in the Cooling System

Man underneath engine repair.

When you find a leak, you must decide whether you can handle it yourself or you need to see a professional.

Radiator Leaks

Tip: If the radiator is leaking badly, I recommend going directly to a reliable radiator shop. If they say it's cheaper to replace it than to repair it, do so.

A Word About Sealer

If you find a small leak in your radiator or engine block (a couple of drops a day, with no need to add water more frequently than once a week), you may want to try a sealer, or stop-leak as it's sometimes called, before you head for a repair shop.

You add sealer to the liquid in your cooling system. It circulates around with the water and coolant, and when it finds a hole where a leak is occurring, it plugs it up.

You can purchase several kinds of sealers. The trick is to choose the one that does the best job without gumming up the cooling system. Ask for advice at the dealership or auto supply store. It's especially important that the sealer be compatible with your coolant (the label should tell you).

Sealers are usually added through the radiator fill hole. Some coolants have a sealer built in, but these are rarely strong enough to deal with established leaks. If you try a sealer and the leaks recur in a couple of days, get professional help. On the other hand, if the leaks occur in any of the hoses, replacing the hoses yourself is quite simple.

Remember: 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 (use the yellow pages to find one), tell themwhat 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 (see Figure 12-9). These plug the holes where sand was removed when the engine block was cast. 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. If replacing them is a high-ticket item, get a second estimate. If that's high, too, check the bluebook value of your vehicle's make, model, year, and accessories on www.kbb.com or www.edmunds.com to see whether it's worth putting the money into it.

Figure 12-9: Core plugs in 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 (see Figure 12-10) are too loose or too tight. If you try to tighten these bolts yourself, you may damage the gasket because the bolts have to be tightened to specifications and you probably 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 more costly.

Tip: You're always ahead of the game if you go to a professional with a good idea of what's wrong and the possible ways to correct the problem. (If you're told that the head gasket has to be replaced before the technician has really checked the head, don't tell the technician what to do; just ask whether it would be wise tojust try tightening the bolts first instead of replacing the gasket immediately.)

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.

Figure 12-10: The head gasket lies between the cylinder head and the engine block.

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 lookingaround 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.

Car Smarts: Originally, the water pump operated in connection with the fan and there was a single fan belt that ran around a pulley connected to the alternator. Almost all fans today are electric and thermostat-controlled, not hooked to the engine or water pump. These fans are mounted to the radiator and only come on when they need to, so they're not part of the water pump system anymore.

Tip: If your water pump needs to be replaced, instead of paying top dollar for a new one, ask your mechanic about installing a rebuilt or remanufactured pump (the glossary explains the difference between these two terms) if such a pump is available for your vehicle and if it's considerably less expensive than a new one. Professionals usually prefer to obtain these parts themselves so that they can make a little profit on the part, but if your mechanic is okay with you providing the pump, there are a few things to keep in mind: Make sure that the pump is designed for your vehicle's make, model, and year; comes with a gasket that matches the old one; and comes with at least a 90-day written warranty or guarantee. If the service facility provides the pump, they should be willing to guarantee it for the same amount of time.

Locating Leaks by Pressure-Testingthe Cooling System

If you can't locate the source of a leak and your vehicle is losing liquid from the cooling system on a regular basis, drive to your service station and ask theattendants 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. Whileyou're at it, have the technician pressure-test the radiator pressure cap as well.

Caution: If you have an old vehicle that hasn't had its cooling system serviced or rebuilt in a long time, pressure-testing the system may dislodge the deposits sealing the weak spots, causing the system to leak. Before the technician starts testing the system, ask whether the procedure is worth the risk.

From Auto Repair for Dummies, copyright © 2009 by Wiley Publishing, Inc., Indianapolis, Indiana. Used by arrangement with John Wiley & Sons, Inc.

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