2000 K3500 Silverado questions 7.4L V8 hog

[MoJoRisin']

Have some questions about my single axle 1 ton beast which has 95k miles:

1) Seems to potentially have an exhaust manifold leak. When cold no problem, drive for short distances with light load - no problem. Drive heavily loaded and hot then I get what almost sounds like a heat shield rattle. This goes on at certain RPM ranges more than others (think resonant frequency vibration). Any ideas on troubleshooting this if it is manifold?

2) Cold weather whine - ONLY when pretty cold (at or below freezing) I get a high pitched whine which moves with RPMS - both in paprk and when driving. I'm leaning towards needing to get tranny drained and filter serviced. Anyone experienced this and had it clear with tranny service? I'm approaching the 100k service point on the tranny fluid so soon I will be having that completed.

 

[mrphoenix80]

For your first question check the Cat. Convertor. When it gets warm I have seen some of these make noise like that. Often the only way it makes the noise is when under load so free reving won't help to isolate it. Use a soft hammer or the like and hit the Cat. if you get the noise then there you go. Normally the manifold breaks off the bolts that hold it to the head and then you get and exhaust leak when cold that goes away when warm. You can do this check by eye.

The whine noise is harder. What kinda noise is it? Does it make that "FORD" (power steering) noise? If iheard it I could tell Ya. The other option is a cheap stethoscope or a loooooooong screwdriver. Touch the various moving parts and find the loudest one that sound like your noise.

Be quick about the Cat. Convertor cause the warranty on it runs out @ 100k

 

[MoJoRisin']

After having the transmission fluid changed and the filter serviced my cold weather whine has been eliminated.

On the CAT I believe it has an 80k mi warranty and therefore is out of warranty. I'll be keeping an eye on it - as said it only seems to be an issue when hot and under significant load.

Thanks!!

 

[Bartonmd]

I've had exhaust heat shields make noise like that, at certain RPM/loads. You might make sure none of the mounting tabs of any of your exhaust heat shields are fatigued and broken.

Mike

 

[deekster_caddy]

FWIW the muffler on my '05 Yukon had the internal baffles break loose and they would vibrate like crazy at idle. It was almost hilarious it was so loud. Ended up replacing the muffler, but the large dual inlet dual outlet muffler was hard to find in something that was quiet like OEM.