Exhaust smell inside car remains a mystery

By Doug McAllister

Q. We have a 2009 Cadillac DTS we bought in 2012 when it had 50,000 miles on it. My wife loves a big sedan as we're all 6-footers and have three grandsons. The DTS was in great shape, but when we test drove it, my wife smelled the odor of combustion gas when she was in the back seat.

My sense of smell is lousy and the salesman wasn't going to say anything, so we bought it as our 2006 (car) had been totaled. Shortly after, the exhaust/gas smell would come and go.

We took it in to a Cadillac dealership and they worked on it twice, for several days. They replace a cowl gasket, the cabin filter and I forget what else. No change.

We took it to our regular mechanic, and the shop couldn't find anything, either. My wife's theory is that being around the smell of gas and exhaust, these mechanics are "nose blind" to it.

The other problem is the smell isn't constant. Sometimes it's terrible, sometimes it's fine. It's always worse when we have the heater on. We find some relief when we have the air on recirculate, but that setting closes down after a couple of minutes and we're back to outside air.

We've looked everywhere to see if there's an exhaust leak, and no luck. I've talked to Cadillac and also no luck. At times, the car actually sickens us, so we crack a window, or drive with the heater off. We'd look for another DTS, but they're hard to find in the first place, and there's no assurance we wouldn't have the same problem.

Any light you can shed on the subject, or referral would be most appreciated. Sorry for the lengthy email.

- Matt

A. Matt, thanks for reading the paper and my column. The problem you are experiencing is a bit challenging and mysterious.

The first thing that would help is to really identify what the smell is. Is it raw fuel? Exhaust? Perhaps the smell of burning oil, either from a leak or a breather tube? A breather tube would give off more of an oil/combustion smell.

I have even seen where a plastic bag got caught under a vehicle, melted to the catalytic converter and the burning plastic smell comes and goes.

Once you can discern what exactly the smell is, a technician should be able to track down the source. Sometimes certain models of cars are prone to having the same problem, but I have not experienced or heard about this concern with the DTS.

I don't know if this helps much but I believe the first step is to tell your service tech exactly what you smell.

• Douglas Automotive is at 417 W. Main St., Barrington; 123 Virginia Road, Crystal Lake; and 416 Northwest Hwy., Fox River Grove. For information, visit douglasautomotive.com. Send questions to underthehood@dailyherald.com.