Troubleshooting a Heavy Rattle Sound in a 6.5L Diesel

Written by Bill Heath Thursday, 17 December 2009 17:05

Volume 2 Issue 1 - 6.2/6.5 Issues and Answers

Our 1996 K-2500 GMC diesel has many mechanics stumped; maybe you folks have the answer. Last summer, while traveling through Oregon, we began hearing a rattling sound under the hood. A shop diagnosed it and replaced the air conditioner pump. No change and he threw up his hands and sent us on our way. Another shop in California, decided it was a bad water pump which they replaced. Again, no improvement and in fact, it had gotten louder as time passed by. Of course, the shop couldn’t very well switch the old pump back on, so we were stuck with yet another unnecessary and costly repair. Then, another shop in Mexico diagnosed the problem as being the alternator and this time, the mechanic ‘proved’ his diagnosis by removing the drive belt so we could listen. Sure enough, the rattle was gone when he did that little test, so on with the new alternator. Same old deal. When the drive belt is on the rattle is there and it is getting worse all the time. The engine runs well and has good oil pressure, so we are hoping it gets us back home to northern New Brunswick next September. Can you offer any help?

Most commonly, a heavy rattle, one that sounds like marbles rattling in a tin can is caused by