engine knock noise inside cabin

[leonuchi817]

Hi everyone. Ive been getting help and info here on tahoe forum for years already and i could really use some help right now.

About a two weeks ago i started hearing a knock/tapping noise coming from inside the cabin out my 2001 Tahoe LS with the 5.3 with 162,476 on the odometer. I put ear up to the radio head unit and i could make out a faint knocking. I opened the hood but i couldn't hear anything.

Some time passed and the noise seemed to get louder. I keep opening the hood and checking but to no success. I finally bought a cheap mechanics stethoscope from Harbor Freight. After a whole morning of trial and error i finally put the scope on the rear passanger side spark plug heat shield and i found the noise! It sounds like someone tapping a pencil on a table. It's not fast. Its more of a steady tap, tap tap, tap. But i can only hear it from inside. It's even worse in the mornings on a cold start. Especially with this cold weather we've been having. Then it turns into more of a loud clanking that you can hear from far away. If i gently press the gas pedal i can hear the noise getting faster. It doesn't sound or feel like a misfire from the spark plug seeing as how i replaced them with AC delco plugs and new not refurbished Bosch wires about 4 months ago.

I'm by no means ASE certified. Just your regular tree shade mechanic. Im guessing the noise is coming from deeper inside the engine and its resonating off the plug.

Im just wondering if its an issue i can fix or have a pro fix it or if its finally time to put her down. I'm really hoping it's not the latter. Hearing a engine knock from inside the cabin can't be good. I'm hoping there are a few master mechanics or some self taught pros that can help me out. I would really appreciate any and all help before i finally take it in for a diagnostic.

Thanks.

 

[Jeff M]

The 5.3 is a push rod engine and therefore uses hydraulic lifters. When a lifter fails to extend a tapping noise will start and will become louder and faster as the engine RPMs increase. This could be the cause of your noise and might be fixed by flushing the engine, I would start with an oil additive (I like Rislone) and try that. You can also use a solvent flush that is designed to only run in the motor for a few minutes and then removed with an oil change. It is also possible that a lobe on the camshaft is failing and in that case it is time for a rebuild but I doubt that is the cause. Also make sure you are using a high quality oil filter, it makes a big difference in getting the fine debris out of the system, I prefer Purolator or Wix. I had a similar noise in my 2005 Tahoe with 155,000 miles on it earlier this year and the Rislone solved the problem. I hope this helps, good luck.

 

[leonuchi817]

Thanks for the speedy reply.

I usually buy quaker state synthetic blend and a fram tough guard filter for $2 more at autozone. I'll try the Rislone. If that doesn't work, do you recommend a flush with diesel? A few people have recommended that that'll fix the problem because of the diesel high cleaning detergents. Also what am i looking at money wise, worse case scenario failing camshaft?

Thanks.

 

[Jeff M]

I personally do not like the Fram, I would highly suggest avoiding them. In my opinion they have great marketing but not a great filter. I have not used diesel fuel to flush with but in the end it probably is about the same thing as the engine flush you buy at the auto-parts store. You do need to be careful if you do use a flush, don't drive with it in the engine just idle it. I have had great luck with the Rislone, I really think that will do it for you.

If the cam fails then you are really looking at a rebuild. While the cam by itself can be replaced, the metallic debris it introduces to the engine will have likely caused other damage to the lifters and engine bearings. Depending if you do the work or take it somewhere will determine the cost.

 

[Hockman]

Engine Knock

I own a 2005 Suburban with 5.3L V8 Flex Fuel - 173K. I have been running Mobile 1 full syn 5w30 and began noticing the knock a while back. When the engine is cold, the knock is not present. As engine approaches normal operating temperature, the knock begins and is RPM related as you mentioned. Mine has progressively become louder and longer before it goes away. Which after running at operating temperatures for a little while (depends but maybe 10-15 minutes) the knock goes away. No performance variation before, during, or after the knock period. I have been told everything from typical Chevy motor, to short piston skirts (i.e. piston slop), sticking lifters, hydraulic lifters, camshaft, etc. I did notice that upon a fresh oil change, the problem seemed better or non-existent. I have to agree that it would seem that the engine flush might help. I am going to try the Rislone product. Was curious if any results has been determined for you. I know it is not the topic of this thread but I would agree on the filters. Napa gold is made by Wix and they are both excellent filters. I read an article where some guy bought a bunch of different brand filters and dissected them looking at the quality and so forth and in the end Napa gold and wix were at the top of his list. You may try googling it. If I find it I might post here.

 

[Hockman]

Here is a good write-up on engine oil filters. Not the one I was thinking about but still good information none the less. Thanks.

http://www.300cforums.com/forums/ge...ble-shooting/31190-oil-filters-dissected.html

 

[Jeff M]

Hockman,

Something else to look at...

I had a noise that sounded almost like a knock but more like a loud tic and only happened when it was cold and it went away when the engine was at temperature. After a lot of looking I found that I had a broken exhaust manifold bolt... so what I was hearing was a rather large exhaust leak located next to the firewall on the driver side. When the manifold and head warmed up the gap closed and the noise was gone. Apparently this is a very common problem with the 5.3.

 

[Hockman]

Thanks Jeff. I will keep that in mind.

What I have done is put approx. 1 OZ to 1 GAL ratio of sea foam in gas tank as well as 1.5 OZ to 1 QT oil ratio sea foam in crank case. The motor oil is fairly new, last oil change around 300 miles ago. I picked up some house name oil filters from O'Reilly Auto and some new oil from Wally world. I am going to do the sea foam in the crank case a few times where I run it in there for about 100 miles or so on new oil change and watch the clarity of the oil on the dip stick (using white rag or napkin). What I think I want to see is a longer period of time before it goes black. Ultimately, I want to clean all the (supposed) gunk out of the engine. When I have another chance, I am going to run sea foam through the vacuum booster line as directed by MFR. This should be the conclusion to the triple point carbon/gunk out process. I am wanting to wait a little on the final step to try and isolate which step solved the problem.

I will keep posting information here about the results throughout the process. If I can remember to take pictures I will try to post them as well.

A little tidbit of news, I talked with the man behind the counter at O'Reilly Auto and he told me that the house brand oil filter is no longer made by Fram but is presently made by Wix! I was surprised but after I thought about it I started to understand. Seems like everything is made by a few MFR companies and than multiple different companies put their stickers on it and repackage it as their own product. He also gave me a little history on motor oil. Supposedly, Pennzoil was the first to come out with synthetic oil!? Also, he said that if you dig through the laws state/federal, you will find various rulings that govern truth in labeling for motor oil. His statement was "in order to put full synthetic on the label, it must be a minimum of 65 - 70 percent synthetic oil"...the rest is just conventional motor oil. The only brands that are truly full synthetic oil according to him are Amsoil and Royal Purple. I have used Royal Purple before and liked its performance but pricey. I have never used Amsoil as it is hard to find around here. I may dig a little to see if I can locate a distributor of Amsoil here in the Dallas area.

 

[Hockman]

Engine Knock

So, follow-up to the use of sea foam in crank case. I ran the oil in the crank case with the aforementioned ratio of sea foam to motor oil for around 250 miles. The oil was new prior to addition of the sea foam. I was surprised how clean the oil still was after running it for that long. I did not notice an improvement though in the knock condition. I feel that my engine is cleaner now on the inside though. I would stress that older engines could develop gasket leaks and lower compression readings if to much cleaner is used and if the engine has been "gunked" up inside for a long time. If you use engine cleaner faithfully since the day the engine is new, than should not be a problem. But as the engine gets more "gunked" the gaskets, which need motor oil to keep them swelled and lubricated, get covered over and no longer have motor oil in contact with them. They shrink and get brittle. Once the "gunk" is removed, the oil leaks in various locations. The compression issue can be explained best by soft metals inside the cylinder, I.e. rings and sleeves. These soft metals are designed to sort of absorb some, i repeat, SOME, of the foreign debris in the motor and when aggressive motor flushing or internal cleaning is performed these "absorbed" debris may get removed and thereby leaving small gaps and holes where the piston combustion chamber is to be sealed off.

 

[Hockman]

How to fix the knock

So, I was perusing through you tube the other day and came across this shade tree mechanic that happens to do a variety of videos. BriansMobile1, here is the link http://www.youtube.com/watch?v=4RecrxxLT4s.

So, he is working on a clients 5.3L V8 and it has this knocking noise similar to what I have and what has been described in this link. Sticking lifter is the culprit here in this video. He takes the valve cover off along with various other accessories and exposed the valves and lifters. Seems like any interesting project for me to try. He uses a motor flush which is used for only a few minute prior to an oil change along with spraying some carb cleaner into the sticking lifters. See video for directions and chemicals used. I think I am nervous to try this as it appears to be quite involved. I am imagining that if you were to really get after it, you should be able to do this at your home in about 3 hours maybe 4 hours tops.

If I get brave, I may try this. The other possibility is rod knock which is much worse. Based on the noise that is heard in the video and the description the person making the video narrates to the viewer and comparison to my problem, I feel comfortable it is a sticking lifter. This may be a more common problem than realized for this motor.

 

[Jeff M]

I have seen the same video in the past and I agree that it is very likely the culprit in your case. The way the engine is built you cannot get the lifter out without pulling the cylinder head so you are correct the best you can do is spray it down and hope it breaks loose. The Rislone did it for me but took a few thousand miles to work. Good luck and let us know how it turns out.