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I sprang a leak in my radiator about a month ago... and I simply did not have time to replace the radiator myself, so I took it to a mechanic. The mechanic replaced the radiator but he reused my old cap.

Two weeks later my water pump broke (basically the bearing broke and the pully was flopping around). Upon replacing the pump (what an ordeal) I saw/read in the instructions that I should also replace my radiator cap along with the new pump!

Now I'm wondering if re-using my radiator cap precipitated the failure of my water pump. Also, how common is this problem? Should I expect a mechanic to replace the cap with the new radiator (I know that should have checked it myself)? I didn't even think about it until I read the water pump instructions, at which point I looked and found my old radiator cap was still in use.

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No. Reusing the radiator cap (almost certainly) didn't cause the water pump failure. The advice to replace the cap is probably based on the logic that the cap is a relatively inexpensive part and renewing it helps to ensure the integrity of the pressurized cooling system. An independent mechanic will often try to use her/his judgment to balance cost and likely benefit. If the cap tested good a reasonable mechanic might decide against replacement.

If the water pump was original you got a good run out of it.

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  • Actually, I replaced the water pump about 5 years ago... so this is the second pump. I guess that sometimes a coincidence is just a cigar. – Ben Welborn Jul 28 '16 at 14:30
  • I think so. If the mileage on the pump seems reasonable (say 100,000+ miles) I'd be inclined to say it was due. – dlu Jul 28 '16 at 14:35
  • I'd put the mileage on the pump at about 55,000. The first pump lasted about 80k mi. – Ben Welborn Jul 28 '16 at 14:37
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    That seems low to me. But I can't see how the radiator cap, which, may well have been good, could lead to a bearing failure. But if the belt were too tight. That could do it. – dlu Jul 28 '16 at 14:39
  • Well, perhaps the cap wasn't good... and the pump was getting old. Now I'm thinking that a bad cap may have been the reason for the radiator leak. – Ben Welborn Jul 28 '16 at 14:40

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