Diagnosis of ugly noise at start up (1 Viewer)

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H

hadmatter

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Nov 23, 2011
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Lately I have noticed a "rumbling" sound that lasts for about 5 seconds when the truck is started (never occurs during cold starts). Used to happen about one in twenty times, seems to be much more frequent now.

'97 w/ 195k miles on the vehicle.

The sound is low and "rumbly".
At first I thought it was exhaust, but ruled that out because it goes away.

Could it be a belt that's too loose? Have replaced all three and they're within spec from what I can tell.

Could it be water pump?? Have replaced all other cooling system components - skipped the pump because the bearings felt time at the time.

Could it be the fan clutch??

Idle is smooth, rpm's are normal - during the rumble and after.

Thanks!
 
My $0.02.
If someone starts the vehicle for you (with you observing the engine) and it makes the rumble you should be able to hear if it's the water pump, IMO. But, that's a decent suspect, though I'd call that sound, when bad, more of a rattle. And they have a weep hole to indicate leakage if that's associated with the failure.
With the engine off, try to wiggle the fan clutch. If it has any axial play, that's not a good sign. An Aisin replacement is very cost effective, as is the official OEM part.
Back to your exhaust suspicion: don't rule that out. Cracks (which I just discovered on my otherwise spotless muffler) or manifold leaks are affected by engine run-time/temp. As metal expands leaks/cracks change.
With you down listening to the underside of the vehicle (in a safe position), have someone in the driver's seat slowly increase revs and then let it drop right off by chopping the throttle. Repeat. The exhaust vacuum created will reveal different sounds from cracks or leaks.
 
ditto on having someone start it as you watch. Also, after you do this a couple of times, take a video and post it.
 
arcteryx said:
actually mine started doing this recently, haven't had a chance to investigate.
Click to expand...
Yeah mind sounds like of like little rocks being thrown around. Never sticks around long enough for me to poke around, nor does it happen often enough to chase it down
 
Park it on downslope and see if it's worse. Curious.
 
Mine does this too... and it is worse when I park downhill... Whats that mean? :/
 
scrowley said:
Park it on downslope and see if it's worse. Curious.
Click to expand...

I'm curious as to why this would matter. What are you thinking Scott?
 
Not sure what it means. Just figured it was same noise. I think something with strainer/oil pickup. but that is a guess.

Mine has done it for awhile. Always very noticeable when cold and park down hill. my rig also smokes worse on startup when parked downhill....not sure if it's related. Worn valve stem seals.
 
Mine does it too, just rebuild and didn't own it prior to rebuilding (bought it blown up)

I was thinking the starter...

Mine also has a tapping noise (like a heat shield or tin) but the weird part is that it's coming from inside the bell housing?!

Doesn't happen all the time, but when it does and you put it in gear it stops? Hmm
 
Thanks Scott. I briefly looked tonight and it happens after running awhile too. Haven't tried a hill . I am wondering if it's a pulley or belt, no squealing though. More investigation needed. But it does sound like rocks being tossed around .
 
I remember reading a thread about it and saying it wasn't big deal so I forgot about it. My 80 didn't make the noise 25 k miles ago though. when listening around its def. in lower engine/ bellhousing area.
And I replaced oil pump cover seal and there was no change in noise.
 
Yes I did the oil pump seal and crank seal and no difference. I use about a half quart of oil every other week. Always felt it was just that but nope.
 
Mine sounds like something's in the bell housing and the flex plate hits it sometimes...hard to explain but it's driving me nuts!!

I've taken the cover off and there's nothing in there, and no sign of any interference or dings on the flex plate...

One of these days I'll find it..if it's the last thing I do!!!
 
Nothing but oem filters here so no dice on that possibility.
 
No more developments on this topic? I was thinkin someone woulda figured this out by now...
 
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