Hello Everyone....
Have a '96 LC with just over 150K on the clock.
Well, i've been searching for about 2 hours and found lots of threads on engine noises but nothing is leading me in a path that seems like my issue.
Starting about 2 months ago, I noticed a rattling or slightly muffled knocking sound coming from what seems like the front of the motor. The sound is random...meaning it seems to start and stop intermitantly as the engine warms up from a cold start. It only happens on cold starts and takes at least five minutes to go away completely with the engine just at idle. Sometimes, even with a cold engine, it does not make the sound at all, and all sounds normal. If you start to drive the truck immediately, the sound is NOT noticeable inside the truck. At idle. if the sound is occurring AND I increase throttle, it IS affected by RPM of the motor....meaning its rhythm increases.
I initially thought it was the water pump, which I just replaced and the sound persists. I also just did an oil/filter change and it had no affect.
Now, I have tried to isolate the sound by using a mechanics stethescope and listening on various parts of the motor or attached accesssories and do not hear the rattle through the stethescope on anything that i've listened to, which include:
the front of the valve cover
the rear of the valve cover
the water pump
the alternator
the a/c compressor
the front of the block
From reading other posts I became convinced that it was either the alternator/water pump belt idler pully, or the a/c belt idler pully, but with the stethescope (carefully!!) touching each of thier mounting bolts with the engine idling, I hear no rattle through the stethescope, leading me to eliminate them as possibilities as well.
The noise does not sound good, and I'd be thinking the worst, except the engine seems to run fine and sound perfect otherwise when the noise is not present. Once it warms up it is gone. Oil pressure and temp are all good and normal.
Any thoughts?? (help!)
Have a '96 LC with just over 150K on the clock.
Well, i've been searching for about 2 hours and found lots of threads on engine noises but nothing is leading me in a path that seems like my issue.
Starting about 2 months ago, I noticed a rattling or slightly muffled knocking sound coming from what seems like the front of the motor. The sound is random...meaning it seems to start and stop intermitantly as the engine warms up from a cold start. It only happens on cold starts and takes at least five minutes to go away completely with the engine just at idle. Sometimes, even with a cold engine, it does not make the sound at all, and all sounds normal. If you start to drive the truck immediately, the sound is NOT noticeable inside the truck. At idle. if the sound is occurring AND I increase throttle, it IS affected by RPM of the motor....meaning its rhythm increases.
I initially thought it was the water pump, which I just replaced and the sound persists. I also just did an oil/filter change and it had no affect.
Now, I have tried to isolate the sound by using a mechanics stethescope and listening on various parts of the motor or attached accesssories and do not hear the rattle through the stethescope on anything that i've listened to, which include:
the front of the valve cover
the rear of the valve cover
the water pump
the alternator
the a/c compressor
the front of the block
From reading other posts I became convinced that it was either the alternator/water pump belt idler pully, or the a/c belt idler pully, but with the stethescope (carefully!!) touching each of thier mounting bolts with the engine idling, I hear no rattle through the stethescope, leading me to eliminate them as possibilities as well.
The noise does not sound good, and I'd be thinking the worst, except the engine seems to run fine and sound perfect otherwise when the noise is not present. Once it warms up it is gone. Oil pressure and temp are all good and normal.
Any thoughts?? (help!)
Last edited:
You came in too late!
