Isolating a Diesel Engine External Rattling Noise

Usually means something is broken or loose in the engine compartment

Here is a list of the possible causes. These are also the most common.  Finding the problem will require a very close visual inspection.  If you think the noise is coming from one of the front accessories on your diesel engine you may have to remove the V or serpentine belt and run the engine BRIEFLY to isolate the noise. With the belt off you can spin the alternator, idler pulley, water pump, air compressor clutch, etc. by hand to see if any are loose. 

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Problem & Solution

Common among these chassis:


Here are a number of things to check

  • Alternator fan pulley or broken bracket
  • Fan clutch worn out
  • Serpentine belt tensioner shock on 601 602 and 603 engines
  • Collapsed rubber motor mounts
  • Broken air filter housing mounts or bolts (common on 617 turbo engines)
  • Loose or broken exhaust outlet pipe
  • Throttle linkage bushings
  • Fuel injector nailing 

The last one on the list is not external, but the sound of a bad injector knocking can fool you.  You might think it is an "external noise".  Be sure to check out Kent's video instruction on isolating diesel engine knocking sounds.

We have other resources available to help you isolate and repair the problem. See related products.