How to tell a mechanic that you'd like to do a repair yourself?

I can tell the difference between an exhaust leak and a rod bearing failure, thank you very much.

They can sound very,very similar at the beginning.

I either do the entire repair myself or I let my mechanic do the diagnosis and the job. I think this is really only the fair thing to do.

Just be honest up front. Tell him up front that you’ll be happy to pay for his time and expertise and if it turns out to be something you can do yourself you’d prefer to do so.

There are some problems that are not conducive to making a clean, definitive diagnosis and then returning the car to the owner for repair. Searching for an electrical short or open circuit or intermittent problem often requires trial and error efforts and dismantling to gain access to a harness connection. Once found the repair is sometimes quite simple. But then, there are often melted insulation that must be repaired and then efforts made to track down the high current draw that damaged the wires. On the other hand play in the steering or knocking in the engine or a miss fire may be pinpointed may be definitively diagnosed with a great deal of certainty and the customer do the repair. It is well within reason to ask that a shop only diagnose the problem and let the owner take the car to do as he pleases with it but many shops would frown on doing so. Shop owners seem to prefer that cars come in ailing and leave cured.

I do all of my own repairs that I feel like doing for the same reasons you do. I started doing my own repairs because I could not afford to pay anyone,now I enjoy doing them If the weather isn’t too bad. However I can’t imagine laying on a frozen garage floor with the rust dropping in your face is worth saving what any good shop makes on exhaust work. Besides, what are you going to do if you pay a diagnostic fee and they put it on the lift and the diagnosis is “it has an exhaust leak” ?