Engine Knock. Is It Rod Bearing or Lifter?

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ChevyGuy3100

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Hi. First of all this may or may not be in the right place, and really has nothing to do with oil... But in a way it does.
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I have a 99 Chevy Malibu with the 3100 V6. It has 221,000 miles on original engine and transmission. The engine has a knocking sound coming from the bottom (oil pan area) and it doesn't go away when it warms up. I've tried a thicker oil, and the noise got extremely worse. It is really bad, then towards the end of the oils life, the noise lightens. But when I change the oil, the noise is back. I'm running Pennzoil 5W-30 with a Wix oil filter. The noise was somewhat going away. That was when I floored it every single day. Well I started trying to drive it easier and ever since the car sounds like a diesel on a hot restart, but the sound fades a but after it runs a while. The oil pressure was 35-40 Psi on a cold engine. I haven't checked it hot. When I start it in the morning, the noise isn't there, but after it runs for 30 seconds the knocking noise comes. It sounds like marbles or something. I can get a video in the morning if you guys need to hear it. Sorry this is so long and thank you guys so so much for your help!
 
If the noise isn't there cold and then starts when the engine warms that is usually rod knock. It may not be, but it is a relatively safe guess.
 
35-40 seems kind of low when cold. My guessing is that the bearings are shot. They are getting enough oil to compensate for the "worn out"/low pressure when at high speed.
 
I had a bearing issue in an engine. It was horribly loud at start up, then went away after about 5 seconds. When warmed up, I heard it only in specific RPM bands.
 
I've seen 3100 engines break the cranks into 3 pieces.Early 2.8s had terrible lower end oiling systems(I know,I had a horrid 83 Camaro 2.8).Seriously,you are fortunate to get 221K out of the "X Car" V6 engine.
 
Hey thanks guys!! Well, no thanks for the bad news!! Hahaha. Yeah the noise isn't there until it runs for about 30 seconds. Then it'll come. Mine is in only specific RPMs also. At idle until warmed up, then above idle. Oh [censored]!! I forgot to add something! When I take the car for a very long trip, and I drive it hard, the noise completely vanishes. But comes back after restart. Why would a Rod knock go away after driving for an extended period of Time? If I run the [censored] out of it, the noise will go away. Weird.
 
Oh wow. 3 different places? Did you mean the camshaft instead of crankshaft? That's insane! Thanks for the kind word. It has 221,000 miles and still can do 0-60 in under 8 seconds. The engine runs so well, it's hard to believe it has a major internal problem!
 
Originally Posted By: ChevyGuy3100
Hey thanks guys!! Well, no thanks for the bad news!! Hahaha. Yeah the noise isn't there until it runs for about 30 seconds. Then it'll come. Mine is in only specific RPMs also. At idle until warmed up, then above idle. Oh [censored]!! I forgot to add something! When I take the car for a very long trip, and I drive it hard, the noise completely vanishes. But comes back after restart. Why would a Rod knock go away after driving for an extended period of Time? If I run the [censored] out of it, the noise will go away. Weird.


No, rod knock is normally pretty pronounced once the oil thins and stays that way. Though often it does only become loud at specific RPM or during a particular RPM range.

If yours goes away, with a hot engine, it may be something else.
 
I have a 2000 Lesabre with a 3.8 V6 in it; 195K. Also a 2004 Impala with a 3.4 V6 in it; 150K. Original everything. You have the same engine. http://en.wikipedia.org/wiki/Buick_V6_engine

On both of these cars, after draining the oil, I can jack the car up onto jackstands (safely supported), lay underneath and remove all 20 of the 8mm pan bolts, the three 10mm bolts on the driver side securing the black plastic flywheel debris shield, and the two 15mm bolts in the front of the pan.

Unplug the electric oil sensor in the front of the pan and drop the pan straight down, wiggling it to the drivers side to clear the oil pickup tube from the pan baffle. There are no further obstructions. I replaced my leaking pan gasket on a Saturday afternoon. You CAN replace bearings from underneath without further engine disassembly. You WILL need a large socket and breaker bar to turn the crankshaft nut and position the crankshaft where you need it. A buddy would be a big help; but not totally necessary.

If I were in your shoes, I'd go to your favorite parts store and splurge about $14.00 on a mechanics stethoscope. Come home and play. Within a few minutes, listen to your power steering pump, alternator bearings, water pump, air conditioning compressor, intake manifold, oil pan front, back and sides. Do the same on your wife's car, kid's car, neighbor's car, work buddie's car, anywhere.

In less than an hour, you'll be an old pro at automotive noises. Rev your own engine and listen to various parts. You CAN figure this out, and probably fix it yourself for less than $100.00

Do you own a torque wrench?
 
With your descriptions, it doesn't sound like a rod knock. What it really is, is anybody's guess. Worn wrist pins, perhaps?
 
Originally Posted By: NHGUY
I've seen 3100 engines break the cranks into 3 pieces.Early 2.8s had terrible lower end oiling systems(I know,I had a horrid 83 Camaro 2.8).Seriously,you are fortunate to get 221K out of the "X Car" V6 engine.


really? I had an 84 s-15 with the 2.8 and it had around 500000km when I sold it. team perfectly and didn't even burn oil. I put 1.6 rockers, a bigger carb, intake and headers. went pretty good.
 
That's awesome. I was wondering about just replacing the Rod bearings. I'm glad that it's easy to do. Yes, the 3400 and 3100 and pretty much the same engine, just a bigger bore? Yes sir, I do own a torque wrench. It's a cheap one so id feel better getting a more high quality one.
 
Maybe a cracked flywheel. It sounds just like a rod knock.

Go start your car, put it in drive, stand on the brake and give it some gas. If the knock suddenly appears or gets noticeably louder, it's probably a cracked flywheel.

Let us know what you find when you do this.
 
You know, I was thinking that. Another thing I was thing was that the piston to cylinder wall clearance was exessive and wasn't expanding enough when hot. I should make this clear. If I drive it for less than 50 miles, the knock is still there, but if I go WOT every time I pull out for 50 miles, the noise is almost gone, if I drive it from Virginia to West Virginia in the big mountains, the noise is nearly gone. The harder I push it, the quiter it gets... Makes me think lifter, but that doesn't explain the noise coming from the bottom of the car.
 
I've tried that. The knock doesn't exist when reving under load. Only when letting off the gas in drive. Really bad in neutral or park.
 
Hey guys. I already have a video on YouTube of the knocking noise, but that is from a long time ago. Would it help you guys out if I get another video and post it? I can do that tomorrow afternoon. You guys are so awesome and helpful!!! I couldn't thank yall enough!!
 
Right after I made that post; I went out into the garage and double checked. The oil pan bolts are 10 mm, not 8.

And zzperformance, Milzy Motorsports, and Hinson Motors sells bearings and all kinds of aftermarket parts for these engines. I had no idea that they are raced. And the bottom end is solid enough that the factory offers them in turbocharged versions; same engine internals.

http://www.zzperformance.com/
http://www.milzymotorsports.com/
http://intense-racing.com/Merchant2/merchant.mvc?
https://www.hinsonsupercars.com/default.aspx

Hope this helps!
 
Thank you so so much! Yes, anything helps! So if I decide to do the bearings, what size should I get? Is there anything else I should do to it? My aunts 99 Century makes almost the same rattle Knock noise, but it does go away after it warms up. It has 75,000 miles. I really do appreciate it man!
 
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