What could be causing this Caddy to go through a new water pump every 12k miles?

Dear Car Talk

Dear Car Talk | Jul 01, 2001

Dear Tom and Ray,

I have a 1993 Cadillac, and my problem is water pumps. Including the original pump, I have had four pumps on this car since buying it new -- an average of 12,000 miles per pump. The first three pumps were new from GM. The last pump, which was installed last week, is an aftermarket pump with a lifetime guarantee for the part only. I wrote to GM and asked why these pumps keep failing (always a failed bearing), and the only advice they gave me was to buy some water-pump lubricant at the auto-parts store. Any thoughts? -- Pat

TOM: Well, that's pretty lame advice, Pat. I guess they want you to lubricate your wallet so you'll be ready to spring for another pump in 12,000 miles.

RAY: Clearly, something is causing these pumps to go bad, and my guess would be a belt that's too tight. If the belt that drives the water pump is too tight (or if it's the wrong belt and it's too short), it could be pulling too hard on the water-pump shaft. That would put extra stress on the shaft's bearing and cause it to fail too soon. And that's exactly what's happening.

TOM: So before this new pump gets ruined, I'd go to your Cadillac dealer and ask the mechanic to do several things. First, I'd ask him to check and see if there's a technical service bulletin (TSB) about this problem. My guess is that you're not the only one it's affecting, and perhaps the dealer has a bulletin by now on how to fix it.

RAY: If nothing turns up, I'd ask him to change the serpentine belt (assuming that it hasn't been changed recently) and have him check the automatic belt tensioner. A faulty tensioner could be pulling the belt too tight. And if it's the fault of the tensioner, you'll lose another water pump, even with a new belt. Good luck, Pat.

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