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Username Post: 97 5.7 Vortec (knock)        (Topic#219999)
Senior Member
Posts: 335

Loc: Mn, USA
Reg: 03-10-05
06-25-09 02:05 PM - Post#1723267    

Today my "97" 5.7 Vortec Tahoe (160,000) started to reveal what seems to be a lower end knocking sound.
The past 6 month's I have noticed at times during start up it would knock once or twice and appear to be bottom end. Was not frequent and very quick to stop. This knock at day's end today was constant and easy to notice.
It ran all day in 95 degree heat, with ac on. I noticed a high end tap or knock for a hour or so, but this has gone down below now.

Oil Filter change just a week ago. Level is correct and pressure good.? ? ?

Posts: 381

Loc: Saskatoon, CANADA
Reg: 04-14-09
06-25-09 02:30 PM - Post#1723281    
    In response to 19hoe97

Hi another 97 5.7L Vortec owner here... never had lower end noise, but in the winter cold mornings I would have a top end ticking for up to 20 seconds... my mechanic said it was likely a lifter... but everything would settle down and no problem while driving... and no noise at all now that the weather is nice and warm/hot.

I have heard of lower end noise like this being the 'ultimate final bad news' that a head gasket has leaked, contaminated the oil with coolant, and toasted the crank bearings .... I hope that's not your problem

Senior Member
Posts: 335

Loc: Mn, USA
Reg: 03-10-05
06-25-09 02:36 PM - Post#1723285    
    In response to rodram

Oil look clean from oil change last week and free of any anti freeze or smell.
I would get that "winter" knock @ start up for a few seconds but this is something all together different.
Seems a deeper tone and lower end.
To darn hot, I was gonna get my trusty sawed off broom handle and start listening to areas.

Senior Member
Posts: 1400
Loc: Edmonton, Alberta
Reg: 05-11-03
06-25-09 08:00 PM - Post#1723529    
    In response to 19hoe97

Audio of the noise would help.

If your inclined to do so, remove your oil filter and cut it open all the way around the ring near the top. Pull it apart and see if you have excessive metal in there.

Josh R.L.
Licensed Automotive Mechanic
1966 Buick Special 2 door
1961 Chevrolet Apache 10 panel van
1995 GMC K2500
2011 VW Jetta TDI

Senior Member
Posts: 335

Loc: Mn, USA
Reg: 03-10-05
06-26-09 03:10 PM - Post#1723992    
    In response to 19hoe97

Little update on yesterdays post.

According to my crew this truck was left running all day (6 hrs) with A/C on while pulling their lawn route of 12 stops.Truck did not move but every 30 minutes.

The truck itself never came close to having a heat problem, and the oil pressure they said was @ or just under 40.

Can a "piston" be heated up and scored under these conditions from under lubrication and heat ?
That's the diagnosis they gave me
Took to a local garage today as it's know is getting worse and can actually hear it thru the exhaust as well.Comes & goes every fifteen seconds.

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