Top Tip: Weep Holes Extend the Life of Your Muffler

Who knew that this little hole could save you hundreds of dollars in costly repairs

A few weeks ago I left my truck running while I quickly ran into the bank. Ten minutes later I left and as I approached the truck, I noticed there was a pool of liquid on the ground directly under the muffler.

I crawled underneath and tentatively put my fingers into the liquid and then to my nose. I thought, why would my muffler be leaking water? Upon further inspection, I noticed a small pin hole at the bottom center of the muffler surrounded by soot. Since my truck is 14 years old, I just figured that I needed a new muffler so I added it to the list of repairs I needed to make.

When I got home, I Googled "muffler leaking water" and came across the term "weep hole". In what appears to be common knowledge to everyone but me, a "weep hole" is a hole that is drilled or punched into the bottom a muffler so that water vapor that condenses can exit. This helps to prevent a steel muffler from deteriorating from the inside out and thereby extending its life.

A closeup of a properly drilled weep hole

Typically, water vapor in a muffler burns off when a vehicle is used for prolonged periods. On shorter commutes the engine may not have enough time to reach normal operating temperature. As a result, the exhaust may not get hot enough to burn off any residual water vapor. When this occurs, the water condenses and pools within the muffler causing rust and eventual failure.

Unfortunately, weeps holes are not an industry standard. Some OEMs have introduced them, some have not. Aftermarket mufflers and exhaust systems are inconsistent as well. I'm fortunate that my 2002 GMC Sierra not only has a weep hole, but that the majority of the exhaust system is constructed of stainless steel.

Even older mufflers will thank you when you extend their life

If you'd like to add a weep hole to your muffler, it is fairly easy to do. Simply grab a drill and carefully bore a hole just 1/16" to 3/32" in size. Done correctly, the weep hole won't damage the muffler and won't change its acoustics. Keep in mind that if you do this, you may void any manufacturer's warranty on the muffler.

If you do have to replace your muffler, look for stainless exhaust systems from Borla, Flowmaster, Magnaflow or Walker. And make sure that anything you buy features a weep hole. Watch the video below to see just how much water your mufflers might be retaining.