2000 Tahoe Limited 5.7l Engine Knocking!

hhsrunner1 · December 11, 2009

Hey guys new to this forum. I have a 2000 tahoe limited 5.7l 350 with 150,000 miles. Recently bought this truck and have begun to notice a loud knock in the rpm range between 1500 and 2000 and gradually diminish if going below 1500 or above 2000 rpm. It seems to occur when under load. If i accelerate very slowly and don't allow rpms to go to high...no knock at all. Recently replaced plugs, wires and distributor cap. plugs are gapped correctly. I had a misfire situation in cylinder 3 prior to the replacement of the cap wires and plugs. I have also had a high pressure injector clean done and new fuel pump. No other check engine lights. I love this truck and would really appreciate any suggestions.

Nytemare · December 11, 2009

That's the sound of a bad rod bearing....sorry to say....well it most likely is. I would have to hear the noise to know for sure. It could also be a wrist pin knocking.

I know guys that have driven for 30K miles or more with bad rod bearings...but it will only get worse...and it will get a real pounding on the highway..as you are in the 1500-2000 range at highway speeds.

Try using 10W40 oil and see if it gets any better...sometimes this will help. Also a quality oil filter, ensuring it has an anti-drainback valve.

If you want to get rid of it, you are looking at a rebuild...at least dropping the crank having it reground, you than get new under sized bearings and put it all back together.

I would just pull the engine and do a complete rebuild...If I was getting that far into it.

hhsrunner1 · December 11, 2009

That's the sound of a bad rod bearing....sorry to say....well it most likely is. I would have to hear the noise to know for sure. It could also be a wrist pin knocking.

I know guys that have driven for 30K miles or more with bad rod bearings...but it will only get worse...and it will get a real pounding on the highway..as you are in the 1500-2000 range at highway speeds.

Try using 10W40 oil and see if it gets any better...sometimes this will help. Also a quality oil filter, ensuring it has an anti-drainback valve.

If you want to get rid of it, you are looking at a rebuild...at least dropping the crank having it reground, you than get new under sized bearings and put it all back together.

I would just pull the engine and do a complete rebuild...If I was getting that far into it.

Thanks for the reply, I had feared that something serious like that was the culprit. I Will probably drive it into the ground and rebuild at that point. I was anticipating a rebuild in the future...looks like it will be sooner than expected. I think the truck is worth the rebuild and a second chance at life. Thanks for the response, it is much appreciated.

rodram · December 11, 2009

... given the age and miles on the odometer one might guess that the 5.7L had previously experienced some kind of head gasket, or more likely intake manifold gasket leak that caused coolant to contaminant the engine oil.... then poofff... your rod bearings are gone...

... so check your oil to make sure it is not currently contaminated.... a chocolate milkshake look, or streaks of white and creamy looking substance on the dipstick would be the dead giveaway

... maybe the gasket leak has been fixed by the previous owner without fixing the end result of the leak (worn rod bearings and crank shaft)

Nytemare · December 11, 2009

... given the age and miles on the odometer one might guess that the 5.7L had previously experienced some kind of head gasket, or more likely intake manifold gasket leak that caused coolant to contaminant the engine oil.... then poofff... your rod bearings are gone...

... so check your oil to make sure it is not currently contaminated.... a chocolate milkshake look, or streaks of white and creamy looking substance on the dipstick would be the dead giveaway

... maybe the gasket leak has been fixed by the previous owner without fixing the end result of the leak (worn rod bearings and crank shaft)

True that

Bearing material and Coolant don't like each other.

Nytemare · December 11, 2009

That's the sound of a bad rod bearing....sorry to say....well it most likely is. I would have to hear the noise to know for sure. It could also be a wrist pin knocking.

I know guys that have driven for 30K miles or more with bad rod bearings...but it will only get worse...and it will get a real pounding on the highway..as you are in the 1500-2000 range at highway speeds.

Try using 10W40 oil and see if it gets any better...sometimes this will help. Also a quality oil filter, ensuring it has an anti-drainback valve.

If you want to get rid of it, you are looking at a rebuild...at least dropping the crank having it reground, you than get new under sized bearings and put it all back together.

I would just pull the engine and do a complete rebuild...If I was getting that far into it.

Thanks for the reply, I had feared that something serious like that was the culprit. I Will probably drive it into the ground and rebuild at that point. I was anticipating a rebuild in the future...looks like it will be sooner than expected. I think the truck is worth the rebuild and a second chance at life. Thanks for the response, it is much appreciated.

Yeah...just try using 10W40 and see if it helps....not 15W40...thats diesel Oil.

hhsrunner1 · December 11, 2009

... given the age and miles on the odometer one might guess that the 5.7L had previously experienced some kind of head gasket, or more likely intake manifold gasket leak that caused coolant to contaminant the engine oil.... then poofff... your rod bearings are gone...

... so check your oil to make sure it is not currently contaminated.... a chocolate milkshake look, or streaks of white and creamy looking substance on the dipstick would be the dead giveaway

... maybe the gasket leak has been fixed by the previous owner without fixing the end result of the leak (worn rod bearings and crank shaft)

I have been through a couple oil changes with it and everything looks good. Nothing out of the ordinary there. I think it is a fairly recent thing, because when we test drove it, it sounded fine. The other thing about it is though, is that in neutral i can run it through the entire rpm range with no problem and sounds great...no knock. it is just when underload inbetween 1500 and 2000 rpm that it knocks. it gives out plenty of power and has good gas mileage. just the annoying lound knock.

Nytemare · December 11, 2009

... given the age and miles on the odometer one might guess that the 5.7L had previously experienced some kind of head gasket, or more likely intake manifold gasket leak that caused coolant to contaminant the engine oil.... then poofff... your rod bearings are gone...

... so check your oil to make sure it is not currently contaminated.... a chocolate milkshake look, or streaks of white and creamy looking substance on the dipstick would be the dead giveaway

... maybe the gasket leak has been fixed by the previous owner without fixing the end result of the leak (worn rod bearings and crank shaft)

I have been through a couple oil changes with it and everything looks good. Nothing out of the ordinary there. I think it is a fairly recent thing, because when we test drove it, it sounded fine. The other thing about it is though, is that in neutral i can run it through the entire rpm range with no problem and sounds great...no knock. it is just when underload inbetween 1500 and 2000 rpm that it knocks. it gives out plenty of power and has good gas mileage. just the annoying lound knock.

Yeah thats pretty common with rod knock...if you give it a shot of gas, than let the throttle go and hit it again...like a "double pump"...you should hear the noise there too cause you will cause a little load. Again...heaver oil will help a little to quiet it down.

I wouldn't worry about it personally...I know lots of guys that have had rod knock for years and still have good strong running engines...and like you said....rebuild when it gets really bad. Or pick up another block and rebuild that one...so that when this one finally bites the big one...you can just pop it out...Install the intake and accessories on the new block, and drop it right in there. This way you can spend a little money here and there instead of the whole cost of a R&R in one shot.