Ticking/Knocking Sound 2005 Tahoe z71

[bradyjames]

Hello,

I'll start off with how much of a resource this site has been to me in the maintenance of my own vehicle. Thanks for all the contributions that have given me much insight. I read a lot, but haven't made too many posts.

I drive a 2005 Tahoe z71 with a 5.3l that has about 170k miles. I purchased the truck a year ago and had it inspected by a third party mechanic and purchased the one owner vehicle after it checked out. Also, the transmission is strong.

On Sat Feb, 1 at 7am in the morning, about 50 degrees outside, when I started my engine I could hear a loud knock or rattling sound. I immediately turned the motor off and let it sit until this morning, Mon Feb, 3 when I drove it on the flatbed tow truck. This morning it was about 45 degrees outside, and the knock/rattle didn't sound near as bad as it did on Saturday.

According to the forum, the knock/rattle could be a rod, a stuck valve, loose heat shield. Any more ideas on what this knock or rattle could be?

Also, as of lately, I've been noticing a slow coolant leak. The truck has never over heated on me, but one bit of maintenance I did when I first purchased the truck was replace the water pump, thermostat, and radiator. Where could my coolant be going?

Looking forward to any responses that could shed light on what's going on with the truck. Also, what questions should I be asking my mechanic?

Thank you,
Brady James

 

[rockola1971]

Theres a big difference between "a loud knock or rattling sound". Which is it? A true knock sound could be a rod bearing getting ready to spin. Typically a main bearing getting ready to spin make a loud growl grinding noise. What you are most likely experiencing is either piston slap or lifter noise. Which is very common on the LS series engine design. If it goes away totally or almost fully then its most likely lifter noise. Run a quart of tranny fluid mixed with your oil right before an oil change (If you do your own changes). *NOTE* Do not drive with tranny fluid mixed with your oil. Just let idle in driveway and warm up for 15mins or so and then drain. Its possible the lifters need replaced. Unless engine was abused I highly doubt you have bearing problems. Piston slap is just a product of the tolerances and piston skirt taper and harmless but can annoy the hell out of some people. Could also be an exhaust leak at the exhaust manifolds. Check for broke of exhaust manifold bolts.
As for the coolant leak you will need to find out where its wet. It takes alot of coolant to leak out before overheating starts especially in the winter. First place id check is the heater hose T's behind the engine up on the firewall. This is a very common leak culprit.

 

[Fless]

Check all of your exhaust manifold bolts. Exhaust leaks up by the engine can sound like lifter noise.

 

[OR VietVet]

Good recommendations but it sounds like it is at a shop since it went on a flatbed. What have they determined is wrong with it, if anything at all? Are they waiting to inspect till you report back from here? My guess is piston slap but as Mike said, a knock is way different than a rattle. May well be an exhaust leak too. If you have read threads here, as you stated, then you know we try to really pin the noise down from the owner, you. You should do a cooling system pressure test to determine the coolant leak location. Mike also mentioned the tees at the firewall. many threads here about them. Any recent engine work done on it? Fluid levels and age?

 

[bradyjames]

I just spoke with the mechanic. He claims that the noise I’m hearing is rocker noise and is common to Chevy. I’ve been driving the truck for a year and I’ve never heard it. How serious is this and how concerned should I be? Could this lead to bigger problems down the road?

As the oil begins to circulate from a cold start, it goes away. I just listened to it and it sounded like it did before I hear the loud noise that I’ve described as a knock or rattle. He also said I was using a cheap oil filter - microguard and that it might not have the check valve required. I’ve been using Mobile 1 Full Synthetic Dexos 2 oil. My most recent change was about 2 weeks ago and the mechanic said the oil level looked fine.

Tomorrow they will put it up on the rack and look for coolant leaks and do a coolant pressure test. The oil looks clear and consistent and the motor is not over heating so the mechanic doesn’t suspect a bad head gasket or cracked block/head.


I will know more tomorrow and report back.

 

[OR VietVet]

What oil filter do you use. I think when he says rocker noise he is actually talking about the common lifter noise we talked about. You can leave the oil in it and change the oil filter and top off oil level as needed. Let us know about the coolant leak test results.

 

[Fless]

He also said I was using a cheap oil filter - microguard and that it might not have the check valve required.

If you're using the recommended MicroGard oil filter it has the check valve.

 

[bradyjames]

Update. Mechanic called after the coolant pressure test and said I was leaking at the thermostat housing. Easy fix. Visually, I never saw coolant dripping or leaving a trail - I guess the engine was hot enough to evaporate it, keeping it from view. Anyhow, I told him to fix it while I'm sitting here at work.

Mechanic also claims that the knock/rattle is just a noisy lifter - said he put a stethoscope on it and couldn't really hear any noise. Suggested I might use some MMO, Lucas Oil, or Rislone to quiet it down. I think I'll change out my oil before I try any oil additives. I'm going to use a WIX filter and switch from Mobil 1 5w30 to Castrol Edge 5w30.

What say you guys?

Thanks

 

[OR VietVet]

Full synthetic oil at all times. Yes, change the oil and filter first and go from there. I have never been a fan of additives, even though I know that some do work, at times and can save a headache.

 

[HiHoeSilver]

Update. Mechanic called after the coolant pressure test and said I was leaking at the thermostat housing. Easy fix. Visually, I never saw coolant dripping or leaving a trail - I guess the engine was hot enough to evaporate it, keeping it from view. Anyhow, I told him to fix it while I'm sitting here at work.

Mechanic also claims that the knock/rattle is just a noisy lifter - said he put a stethoscope on it and couldn't really hear any noise. Suggested I might use some MMO, Lucas Oil, or Rislone to quiet it down. I think I'll change out my oil before I try any oil additives. I'm going to use a WIX filter and switch from Mobil 1 5w30 to Castrol Edge 5w30.

What say you guys?

Thanks

Agreed on oil change. @iamdub has reported a disappearing lifter tick with penzoil platinum.

I run M1, but the new Rotella Gas Truck is in the spotlight lately with some impressive numbers. I will probably try it next.

MMO or Lucas wouldn't hurt if its still ticking after new high quality oil.