Noise at Cold Start - Idler Pulley? (5 Viewers)

[taylort232]

Well, I was wrong about the AC clutch. After a day or so of not having the AC engaged, the noise came back. I replaced all 3 belts, both idler pulleys, and still have the noise. In the second video I posted above, the sound is super clear - it's light a low knock sound that comes and goes. When the engine is making that sound, the lights dim and power is weak. It honestly sounds like it's coming from inside the engine.

Edit: My oil was low about a quart, and I've been reading about the hydraulic timing chain tensioner. I just filled it back up - could that be a contributor? Will see if it goes away tomorrow.

 

[mudgudgeon]

Well, I was wrong about the AC clutch. After a day or so of not having the AC engaged, the noise came back. I replaced all 3 belts, both idler pulleys, and still have the noise. In the second video I posted above, the sound is super clear - it's light a low knock sound that comes and goes. When the engine is making that sound, the lights dim and power is weak. It honestly sounds like it's coming from inside the engine.

Edit: My oil was low about a quart, and I've been reading about the hydraulic timing chain tensioner. I just filled it back up - could that be a contributor? Will see if it goes away tomorrow.

A quart low on oil is not gonna make a difference. You still have 7 or 8 litres of oil.

 

[taylort232]

For anyone who finds this thread in the future, it was the harmonic balancer. It mostly only made that noise when the AC compressor was on. After reading a few of these that ended with the same problem, that sounds like a common thing.

Based on the condition of the rubber and the lack of oil leaks in the area, I think this is a preventative maintenance activity on these trucks at this age.

 

[Kernal]

In 20:20 hindsight (after watching all the videos) that low rumble rattle sounds like a large chunk of metal intermittently sliding/rotating/wobbling. So wondering if when the AC compressor was engaged the AC belt was now pulling more in the opposite direction (torque) from the alternator belts which may have made the wobble of the separated harmonic balancer more pronounced??

Glad you figured it out, good info for the hive mind.

Agree about considering this a PM after 25 years, do it at the same time as the oil pump cover and front crank seal replacement.