Is a weird smell and fluid on your tires a major car problem? Here’s what you need to know!

Dear Mike,

I need some car advice. Lately, I’ve been smelling a weird odour coming from the back of my truck. On top of that, I’ve noticed some kind of fluid on the inside of one of my tires. I’m not sure what’s causing this, but I’m worried it might be a major problem. Can you help me out?

Thank you,


Dear Brendon,

First of all, let me congratulate you on your keen sense of smell and observation skills. Many people wouldn’t have noticed these subtle signs, but you’re clearly a sharp-witted car owner. Now, let’s get down to business.

Based on the symptoms you’ve described, the most likely cause of your issue is the differential fluid leaking through the vehicle’s rear axle seal. Don’t worry if you’re scratching your head and thinking, “What the heck is differential fluid?” I’m here to explain it to you in plain English, without all the fancy jargon that mechanics like to throw around to sound impressive.

Differential fluid is basically a special oil that lubricates the gears and bearings in your truck’s differential, which is a fancy name for the part of your car that transfers power from the engine to the wheels. Think of it like a middleman that helps your wheels turn smoothly.

Now, the rear axle seal is a tiny rubber ring that sits at the end of the rear differential at either wheel, to keep the differential fluid inside. But over time, thanks to factors like wear and tear, this seal can get damaged and start leaking fluid. When enough differential fluid leaks through the seal, it can get onto the rear brake friction material, which is a fancy name for the pad that helps your brakes stop your car.

If this goes unnoticed, the brake friction material will become saturated and will require replacement. And trust me, that’s a lot more expensive and annoying than just replacing a simple seal.

But the good news is that this is a very common issue, especially on modern trucks and vans. Most dealers and proactive service providers, like my own Urban Automotive, will have an inspection process when the vehicle comes in for service to look for just such a condition with the intent to proactively resolve a potential issue before it happens. So if you bring your truck in for a regular check-up, they’ll be able to catch any seal leaks and stop them from causing bigger problems down the road (pun intended).

So Brendon, don’t panic. This is a fixable issue, and one that many other car owners face from time to time. Just bring your truck in for a check-up with a reliable mechanic sooner rather than later, and you’ll be back on the road in no time.

In the meantime, try to enjoy the unique smell of differential fluid. It’s kind of like a mix of burnt toast and old socks, with a hint of motor oil. Who needs air fresheners when you can have that in your car, right?

Yours in automotive odor,

Mike Urban
Founder of Urban Automotive