Could Laura's cascade of problems be related-- or is it just bad luck?

Dear Car Talk

Dear Car Talk | Mar 01, 2009

Dear Tom and Ray:

Love the column, hate that I now have a reason to write to you myself! I have a 2001 BMW 325xi, which I have serviced regularly at a local independent BMW mechanic (and I do mean regularly -- that stupid car always has some "little" $400 thing wrong with it). The shop came highly recommended, and I've never had reason to question that. But then ... last week, the coolant light came on. I took it in to get it topped off. They told me my water pump needed to be replaced, so I did it -- $450. Two days later, while idling in a parking lot, the car went boom! The shop now tells me that the coolant expansion tank blew, and that it's not related to the work they just did. That was $600. Now I'm thinking, wait a minute: No problems with the cooling system for seven years, then two in two days? But the shop says there's no connection, that they see this fairly frequently on BMWs after they hit about five years old, that they pressure-tested the system after they finished and that there were no problems. Sounds reasonable, and they're going to cut some of the labor costs for the second repair. But I have no mechanical knowledge to know if they're legit or just blowing smoke (like my car). So, which one's the lemon -- the car, or the mechanic? (Please tell me it's the car --that's a lot easier to replace.) -- Laura

RAY: I don't think this is necessarily a crisis of car or mechanic, Laura. The most common reason a coolant expansion bottle explodes is because the car overheats.

TOM: And it's possible that the overheating was your mechanic's fault. That may be why they're eating some of the labor cost -- guilt. Or maybe you're just cute.

RAY: If they didn't bleed the cooling system correctly after replacing the water pump, they could have left air in it. Air doesn't do nearly as good a job of cooling the engine as coolant does. That could have led the engine to overheat and blow up the expansion tank.

TOM: But that's not necessarily what happened. Your thermostat could have gotten stuck after the water pump was replaced -- just a coincidence. Or the thermostat may have been the reason the coolant light came on in the first place, and they just happened to notice that your water pump was leaking and assumed that was the issue.

RAY: The worst-case scenario is that all of this overheating is due to something like a blown head gasket. But we rarely see head gaskets fail on these cars. On the other hand, we do see a cracked cylinder head every so often. Hmm.

TOM: Here's what I'd do, Laura. Keep an eye on the temperature gauge for the next few weeks. If it's normal, I think you're all set.

RAY: But if you notice that the engine is running hotter than usual, take it back and ask your guy to investigate a little further. And if nothing else, have him throw in a new thermostat, which is cheap.

TOM: But I wouldn't give up on him or the car over this. Look at it from his perspective: You've been a very good customer for him. Why would he risk losing your business over a few hundred bucks when, during the next 10 years, you could be worth a 28-foot Sportfisher to him?

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