Rick's Free Auto Repair Advice

Fix a coolant leak

How to fix a coolant leak

Can you fix an antifreeze leak with an off-the-shelf stop leak product? Sometimes. But radiator stop leak products work for small leaks, but only if they’re used properly.

More radiator stop leak is NOT better

Most people think that more is better—that if a single dose didn’t stop the leak, a double dose will. Not true. If you use more than the label recommends, the stuff can do more harm than good. Keep in mind that radiator stop leak works by circulating a certain dosage of small particles throughout your cooling system. Since the cooling system is under pressure the particles are supposed to plug the small leak, like a finger in a dike.

But if you overdose, the concentration of particles is so high, that they tend to settle in the smallest spaces, and that’s usually in the heater core. If you’ve ever had a clogged heater core on any vehicle made since 1980, you know that it’s usually a $1,500 repair. A radiator costs about 1/3 that price. So why risk ruining a perfectly good heater core to salvage a $300 radiator?

Stop leak won’t fix a leaking water pump

Don’t even think about using a stop leak product to fix a leak in a water pump. It won’t work—at all. That’s because water pumps leak due to a worn seal. And the shaft is always rotating against the seal. Bottom line, stop leak products don’t seal moving parts. So don’t even try it.

Best radiator stop leak products

For small leaks, I like Bar’s radiator stop leak pellets.

stop leak, radiator stop leak, cooling system stop leak

Radiator stop leak pellets

Just follow the dosing instructions for the number of pellets to use with your system. Then crush the pellets inside a rag and dump them into the radiator and drive the vehicle. Just keep in mind that if you change the coolant down the road, you must re-dose the system or the leak will return.

For medium leaks, use one of Bar’s liquid products. But read the label and get the right formula for your particular coolant. All coolant formulas are not the same and the stop leak must be compatible with your coolant.

Finally, in case you skimmed this article and didn’t get the message, don’t overdose your vehicle. More is NOT better. If the stop leak doesn’t work, quick screwing around and replace the leaking part.

© 2012 Rick Muscoplat


Posted on by Rick Muscoplat

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