A couple of weeks ago on the first cold morning of the fall, I started my R56s and it sounded like a diesel for about twenty minutes of driving in the cold. This kept happening on cold starts. While driving with the windows open on this beautiful afternoon, I noticed that the diesel sound was coming from below the driver's seat and that it went away after about five minutes of driving.

I've concluded that I probably have a small crack somewhere in my exhaust system, or maybe a bad seal that is sealing the exhaust leak when it warms up. Is this probable based on the symptoms I've described?

I have to take my car in for a state inspection before the end of this month. I was planning on taking the car into the dealer to get the inspection, but now I think that 1) it probably won't pass a state inspection with a crack in the exhaust and 2) the exhaust repair will probably be pretty expensive. Does anyone know what these kinds of repairs cost?

At first I thought an exhaust repair would be a pretty simple matter of taking the old exhaust off and putting the new one on. After reviewing the Bentley manual, however, I see that it is likely to be a long and complicated repair. The fact that the repair is likely complicated pushes me toward taking it to the dealer instead of a independent shop, as anything that the dealer messes up will be a lot easier to resolve.

Is repairing the exhaust complicated? Any other thoughts?

 

You've confirmed it's coming from under the car and not the engine bay area? A leaky exhaust system is usually far noisier than an intact one so if you noticed an increase noise from that area it could be the an exhaust issue. I'd maybe put the car up and get under it and have someone start it to see if you can determine where it's coming from and if it's indeed an exhaust leak. If it is, we have a DIY here that can help with the removal. Let us know what you find!

 

It's a tough call, because the engine bay and the front end are so close together. The noise doesn't really affect performance, however, so that seems to cut towards an exhaust issue.

I don't have a lift, so I guess the dealer will have to get to the bottom of it!

Would there be a seal if it were coming from the exhaust, or is that more likely going to have to result in replacing the entire underbody exhaust assembly?

 

Usually when people describe their MINI as sounding like a diesel I've seen it be a timing chain guide issue. Check this thread here, but it was more apparent for him once the car was warmed up. May not be your issue at all. If you have a jack and stands, you can get under your MINI this way. Or maybe at cold start, walk around your MINI, pop the hood and investigate further, and even maybe get down on the ground and listen towards the center of the exhaust for the sound you're hearing. Any MINI indy shop should be capable of a diagnosis for you as well if you don't want to go to a dealer. For the exhaust it could be a gasket or maybe a hole somewhere. If there is a hole you might be able to get it welded, depending on where it is, or you could just possibly replace that section of the exhaust. I'd be surprised if you had to replace the full exhaust. You can see the sections of the exhaust from the first image in that link I posted above.

 

I thought about the timing chain. However, my initial timing chain was replaced in October of 2013, along with the guides and tensioner, as a warranty repair. Do you think that it would need replacing again?

 

Do you have a sound clip ?