It's true. Working on your own stuff can cause other problems (I recently, while fumbling around with vacuum lines, broke one of the valve nipples: now my tranny doesn't shift right...).

But, I like to think (and I'm almost entirely positively absolutely sure about this) that mechanics do the same thing. The only difference is that a mechanic may not tell you about it for a variety of reasons. Like:

A. The mechanic factors it into the cost up-front ("I know I'm probably going to break that part getting that one off, so I'll add that to the estimate")

B. The mechanic tells you that "due to unforseen factors the bill now has to be higher." (oops!) Or "this or that was also broken, do you want me to fix it? ($)"

C. The mechanic deems the new problem not worthy to repair: like, it won't cause a problem for say, another few thousand miles and you'll never trace it back to their shop.

D. The mechanic is an honest one who owns up to their own mistakes, respects that it was they who messed up, and fixes the problem without you being any the wiser.

Hopefully, your mechanic is "D," or a variation on "D," who tells you all about his mis-haps, service gratis.

When you are your own DIY mechanic, you (usually) know exactly what you've screwed up and can be 100% responsible for it, which is better than playing mechanic roulette, if you ask me. And in the end, even with the mistakes I've made, I'm still paying less than I would to have the job done right in the first place. Furthermore, the knowledge one gains by working on their car is invaluable: for example, just think how much more you know about exhaust systems and the work required to repair them now? That knowledge is not worthless, in my book.

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marshall

1982 300TD (220,000 mi.)

This is why I don't work on other peoples MB's. My friend wants me to do a brake job on his S320 and change the serp belt and oil, all easy stuff.

However if I break something I am responsible, and I am not a mechanic nore do I want to be.

Just for this reason I don't work on other peoples cars. Its bad enough when I screw something up on my car, I don't want to have someone else yelling at me.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200