Why Lug Nuts Swell and What You Can Do About It

To be honest, even with over 50 years in the automotive repair industry, I never heard of the expression “lug nut swelling.” When I asked one of my automotive experts, ASE master technician Tom Diamond, he explained what it was. It was only then I realized I’d dealt with this problem hundreds of times.

Living and working in the “salt belt,” the northern sections of our county where tons of salt is spread on the roads during snowstorms, causes the metal in our cars (particularly metals exposed to the elements) to rust and corrode, leading to issues like lug nut swelling. Lug nuts are as critical a safety item on our cars as brakes and steering and should never be taken for granted. Over my career, I have seen firsthand the damage that failed lug nuts and wheel studs can cause and the havoc they can wreak.

Read along to learn about lug nut swelling, what to do if your lug nuts suffer from this malady, and how to prevent lug swelling from happening in the first place from ASE master technicians and industry experts.

Are Swollen Lug Nuts a Thing?

Yes, swollen lug nuts are a “thing,” and yes, they are a real problem. To enhance a vehicle’s appearance, many lug nuts come covered with a separate piece of finely finished metal, usually chrome. Rust and corrosion can build up between the ornate cover and lug nut, causing the covers to swell. Once swollen, lug nuts can be exceedingly difficult to remove using basic tools. If you’re lucky, your mechanic will have to deal with them before you have to change a flat tire, attempt a DIY tire rotation or replace brakes on your car.

It’s not just the lug nuts that rust attacks, either. The exposed threads of wheel studs that the lug nuts screw onto can also rust. So, even if the lug nuts themselves are in good condition, their threads can become damaged and ruined as they pass over the bloated and crusted wheel stud threads during removal.

• PRO TIP: Always replace lug nuts or wheel studs; never attempt to repair or rethread them. Additionally, Don Sutliff from Permatex Inc., one of the world’s leaders in automotive chemicals, sealants and adhesives, says that due to the “extremely low coefficient of friction, Permatex does not recommend using any lube or oil, including anti-seize compound, on lug nut threads.”

What Causes Swollen Lug Nuts?

Electrolysis (or galvanic corrosion) causes swollen lug nuts. Electrolysis is a chemical reaction that generates an electrical current, which passes between dissimilar metal parts through rain, dirt, salt air or saltwater releasing corrosion-causing oxides.

Lug nuts are steel while the attractive fancy covers are made from chrome. The oxides cause metals to corrode and then swell (think of rusted rebar cracking through concrete), which causes the chrome cover to expand, deform, and become rusty, most likely caused by overtightening or using the wrong tools. “Over-tightening lug nuts is just as dangerous as under-tightened [lug nuts],” says Diamond, and he recommends always using a torque wrench to tighten lug nuts.

Are Swollen Lug Nuts Dangerous?

Yes, swollen lug nuts can be dangerous. Once the outer cover expands due to rust, the factory-supplied lug wrench will no longer properly fit over the swollen lug nut.

COLIN TEMPLE/GETTY IMAGES

I have seen where rust buildup was so severe that the chrome covers fell off the lug nut. This is equally problematic because, without the cover, the lug nut itself is smaller than the factory-supplied lug wrench. This can cause the lug nut to round off or the lug wrench to slip off the lug nut during loosening or tightening, potentially resulting in an injury.

Immediately install new lug nuts if you see the covers missing from your car’s lug nuts.

How To Remove Swollen Lug Nuts

Jody Connelly, ASE master technician and MAC Tools distributor, recommends using an 18.5 or a 19.5mm half-size socket (instead of a 19mm/3/4-inch) designed for chrome-covered lug nuts. Diamond suggests using a half-size 17.5mm socket designed specifically for lug nuts with missing or distorted chrome caps.

If the lug nuts are in really poor condition, you may have to use twist sockets that are hammered onto the lug nut. If you are using twist sockets and you have a 1/2-inch drive impact gun, now is the time to use it. Several times I have had to use an air hammer to chisel off really damaged lug nuts. Leave this to the pros. One slip, and you’ll be looking at a deeply gouged wheel. Diamond added, “I always install new lug nuts if I have to use a half size or twist socket to remove lug nuts.”

• SAFETY NOTE: Always wear safety glasses when hammering on a twist socket or using an impact gun.

How to Prevent Swollen Lug Nuts

With proper care and the use of tools designed specifically for removing and installing lug nuts, they should easily last for the life of your car. However, using the manufacturer-supplied lug wrench, chrome (non-impact) sockets, or low-quality 6- or 12-point sockets can loosen or damage the chrome lug nut cover. This damage allows water, dirt, or salt to get between the two parts, promoting corrosion and rust buildup.

Diamond recommends “using 1/2-inch drive, thin wall, deep impact sockets with plastic sleeve lug nut cover guards sockets.” These sockets are designed to protect the lug nuts and covers, as well as the wheels, from getting damaged when removing and installing. “Although it’s tempting to use an impact gun to remove and install lug nuts, it’s best to use the protective sockets with a breaker bar to loosen lug nuts. [When installing] snug the lug nuts by hand with the wheel off the ground, and finish tightening with a torque wrench [in a “star” pattern]” said Diamond.

The Experts

• Tom Diamond has over 35 years of experience in the automotive repair industry as a technician, certified original equipment manufacturer (Mazda) trainer and shop supervisor. He has been an ASE Master Technician for over 25 years, including ASE L1 advanced automotive engine performance certification and is a PA Department of Transportation certified state safety, emissions and reconstructed vehicle inspector as well as a certified welder and now is the automotive technology instructor for the Faulkner Institute at Father Judge High School in Philadelphia PA.
• Jody Connelly has over 20 years’ experience in the automotive repair industry, is an ASE, Mazda and Chevrolet Master Technician, served as service manager and is a PA certified emissions and safety inspection inspector. Jody left the “car wars” to become a professional tool distributor for MAC Tools (Gold Level), providing technicians with the latest tools, technology and training to diagnose and repair today’s complex vehicles.

Resources

• Don Sutliff is the senior product specialist at Permatex Inc., in Solon, Ohio and has firsthand experience with automotive compounds from working in the specialty chemical industry.
• William “Bill” Guzenski has produced hundreds of how-to videos for the automotive community. He’s an ASE Certified Master Automobile Technician and is affiliated with the Specialty Equipment Market Association (SEMA) and is the contact center manager and director for analytical skills at CarParts.com.