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fdryer 01-07-2020 11:18 AM

Re: Unknown engine noise when cold
I have two flex pipes on my L300. Both cracked their internal corrugated section with black exhaust covering the stainless braid used in flex pipes. The outer rings rusted then broke away leaving a ring to vibrate. I simply jacked up the car, removed a wheel then started the cold engine and felt the flex pipe by hand. A cold engine won't heat up the exhaust system for at least a minute or two, enough to feel for exhaust blowing past a hole in piping. The upstream flex pipe is just past the first bend on a downpipe. The second flex pipe is further downstream, before the catcon. It was found leaking the same way, corrugated section broken and leaking exhaust thru its stainless braid cover. Exhaust pressure pulses are felt before the pipes get hot. Same sounds at startup then lowering as the pipes heat up, expanding to close off the cracked section. Mine's a 3.0L V6. The rest of the exhaust pipes are fine. GM was smart to use stainless exhaust to prolong exhaust systems as emissions creates water that can corrode from the inside out. Unfortunately the corrugated section of flex pipes are not stainless.

bumpdraft 01-07-2020 11:47 AM

Re: Unknown engine noise when cold
fdryer, Are you sure the flex section is not stainless? On my SC2, when the original downpipe corroded at the clamp, I bought a very expensive O.E. ([I]Hecho en Mexico[/I]) downpipe and cat.
Some Einstein at the shipper made the unit much more shorter by folding it at-the-flex 180-degrees and taping it. As a result, the wire braids all broke and the flex section is unsupported. It is jumping around under the car and, 8 years later, is still unmolested and intact.

Start-up noise: When my car sat for a year after it was wrecked (while I was stopped for a school bus), some on-line Einstein suggested I pack the oil pump with Vasoline just like a rebuilt 1974 Chevy small block. I did, (like a f-iní idi:drool:t), and a lifter has ticked ever since.

can0fspam 01-07-2020 01:42 PM

Re: Unknown engine noise when cold
Alright, sounds like it probably is an exhaust leak then. I'd be okay with that (although I want to track it down when I can).
I've looked at my flex pipe before when I was diagnosing a noise caused by my belt tensioner. It doesn't seem to be loose at all although I wasn't exactly sure what to expect from it.
With that being said, I wouldn't be surprised if the exhaust manifold was cracked, warped, or improperly sealed. That would explain why the noise comes from the front of the motor and can't be heard on a stethoscope.

I really was mainly hoping it's not timing chain. Does a bad chain *need* to have slack in it (visible under the valve cover) in order to be going out? Because mine looks and feels just fine.

fdryer 01-07-2020 02:30 PM

Re: Unknown engine noise when cold
bumpdraft, the outer braid is stainless, not the inner corrugated section. Each of mine went at different times with the front one going first after around 12-13 yrs/85k miles. The second one about a year later. I do almost all maintenance and under the car for most service so I tend to see things but wasn't expecting exhaust system problems until similar startup noises began followed with quiet after engine warm-up. The rings on each end of the stainless wire braid rusted and broke of its weld as the beginning tell tale as it rattled freely on the pipes. Once noises got louder from repeated startups, I began to suspect the flex pipe damage. Verification from feeling the flex pipe on cold engine startup before the exhaust system heated up. Both were found this way. Stainless is harder than regular steel so it may not lend itself to being formed into corrugated tubing for flexing. It's my suspicion only and I can be wrong as I haven't researched it to prove otherwise.

I never suggested packing the oil pump with Vaseline to prime an empty oil system. I've never come across this suggestion in factory engine assembly so the idea may be from engine rebuilders as a way to get oil pumped into the system sooner. With serious engine rebuilders, my guess is they lube everything for initial protection against dry metal to metal wear. The thick prelube assembly grease may be all that's needed, applied to the oil pump gear and housing as the initial seal to promote suction when the engine is turned over the first time. My understanding of hydraulics is that grease, oil or water act as seals in enclosed volumes; water pumps, shock absorbers, hydraulic cylinders used in light to heavy duty equipment, brake systems, etc. Engine oil pumps only need some lube oil to create a temporary seal to draw in fresh oil from the sump a few inches below. Monitoring the oil pressure gauge is all that's needed to observe when oil is picked up and pressurised to open the pressure switch, turning off the oil light. A genuine oil pressure gauge fed oil from the pressure fitting will show the same but as actual pressure.

fdryer 01-07-2020 02:46 PM

Re: Unknown engine noise when cold
can0fspam, I would suggest a cold engine startup with hood open and feeling the exhaust manifold before it gets hot. To have a good idea of your exhaust system, feel it before starting to see if there are any sharp edges that may cut skin so you can determine how quickly to move your hand over the exhaust manifold. If a thin cotton glove fits and won't interfere with feel into tight areas, you'll need to be a little more sensitive to exhaust leaks blowing onto fingers. Don't just listen for noise as your hand aren't ears but can feel moving air. In this case you're feeling for escaping exhaust from anywhere on the exhaust system that's supposed to be sealed against exhaust leaks with the only opening at the end of the muffler. Moving your hand over the exhaust system doesn't mean just sliding it as you can home in by touch then moving to another spot. If you summon your inner 'Zen', imagine blowing exhaust from a crack and knowing it how it should feel on your fingers before getting burned. Listen and feel. It's not rocket science to use the senses we are borne with.

can0fspam 01-07-2020 05:08 PM

Re: Unknown engine noise when cold
I went and felt for an exhaust leak before driving today. Nothing yet, nothing was obvious.

I did however get this video of the noise reacting to some throttle input, tell me what you guys think:

onlinebiker 01-07-2020 05:35 PM

Re: Unknown engine noise when cold
The flex pipe just before the catcon can exhibit these symptoms... You may have a crack in the flex that gets smaller when it heats up and expands....

fdryer 01-07-2020 05:48 PM

Re: Unknown engine noise when cold
I'm inclined to believe noise is initial loss of hydraulic pressure from clogged valve lifters, making noise from metal to metal contact until hydraulic pressure develops to separate lifters from cams to silence the noise.

Thanks for taking the time to video. It helps to put anyone reading your post almost next to the car to see and hear what you're observing.

There are good suggestions about temporarily coping with valve lifters clogging. Xmission or heavy weight motor oil may provide a temporary solution and help diagnose whether or not its valve train noise or not. Similar to suggestions to run your hand over a cold exhaust system as a cold running engine won't heat up quick enough to feel parts of the exhaust for pressure leaks.

can0fspam 01-07-2020 06:31 PM

Re: Unknown engine noise when cold
Maybe it could be, but I'm still worried it's a chain noise. However I don't see how a chain could fluctuate like that based on temperature alone.

Waiex191 01-07-2020 06:55 PM

Re: Unknown engine noise when cold
I would think the chain would get looser with temperature.

billr 01-07-2020 07:25 PM

Re: Unknown engine noise when cold
[I][B]"I would think the chain would get looser with temperature."[/B][/I]

No, the aluminum block and head have a greater thermal expansion rate than the steel chain. The center-to-center distance between sprockets increases faster than the chain length. Plus, the (steel) sprockets are also increasing slightly in diameter, taking up more chain. Yeah, even the plastic guides expand and push in a bit further on the chain...

can0fspam 01-07-2020 10:02 PM

Re: Unknown engine noise when cold
Since I can see it in person, I can tell the noise is coming from the chain-y area of the engine block. Thank you for all of the advice and ideas of course -- I'm glad we could (mostly) rule out lifters and that I know it's not the belt drive.

Luckily, the noise is gone when the engine's warm which means I think I'm good to keep driving it as long as I take it easy until it warms up. It's survived 7 months and 14,000 miles of me doing that so far with no change in the noise, and I'm sure it's been doing this for much longer with the past owner.

I'll plan to get a chain kit and redo it once I get a break from college, but unfortunately classes start tomorrow and I commute, so I need to drive the car daily.

fdryer 01-07-2020 10:35 PM

Re: Unknown engine noise when cold
Checking the exhaust system for pinhole leaks by hand is free. Mixing in a quart of xmission or thicker motor oil costs a few dollars to find out of the lifters are clogged and silenced with some xmission or thicker oil. I think its much easier to spend a few dollars to find out rather than put all your eggs in one basket presuming the timing chain is the problem. Personally, a timing chain that's worn continues to make noise whether the engine is cold or hot. My opinion but I can be wrong if others can explain how heat can make a noisy timing chain disappear after the engine warms up. You did state the chain was tight and I presume this was checked on a cold engine? In my mind a tight timing chain checked cold can't loosen as the engine heats up. The automatic chain tensioner also comes into play as it adjusts automatically for chain slop with hydraulic pressure from the oil pump to take up slack.

can0fspam 01-07-2020 11:39 PM

Re: Unknown engine noise when cold
I'll keep trying your suggestions in the meantime. Hopefully it's a simple issue but I'm going to be prepared to replace the chain -- and it would be good preventative maintenance anyways.
Car has 188k on it, no idea if it's been changed before.

Thank you for the help!

billr 01-08-2020 12:38 PM

Re: Unknown engine noise when cold
Those chains are not a "maintenance" item that needs to be replaced periodically, and they are not that much fun to change. It should last until the engine needs to be opened up for some other common problem (like a burned valve) or until bearings/rings are shot; probably over 300K miles.

Have you removed the valve cover and inspected the chain and upper sprockets with the engine cold? Be sure to rotate the engine several revolutions to see [I]all[/I] of the chain length.

can0fspam 01-08-2020 02:08 PM

Re: Unknown engine noise when cold
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I have inspected it with the valve cover off. I didn't turn the engine with it off, but the chain had almost no slack in between the cam gears up top. However i think it's still possible for it to generate slack when the engine is ran.

billr 01-08-2020 03:03 PM

Re: Unknown engine noise when cold
Did you push down hard on the chain, did you rock the engine back-and-forth to try maximizing any slack at that top point (the valve springs will often try to move the cams and take up slack right there)?

If there really is little slack up there, and no other obvious problems like badly worn sprockets or broken chain link or missing chain bushing, then I would [I][B]for sure[/B][/I] leave that chain alone!

I gotta say... noises are notoriously hard to pin-point the source. They can often sound like they are coming from a [I]completely[/I] different place than they actually are.

fdryer 01-08-2020 03:05 PM

Re: Unknown engine noise when cold
With spark plugs removed, compression is lost so turning the engine over by hand using an appropriate socket and long pry bar is easy. Even bump starting will work; momentarily flicking the ignition key to START for less than a second to turn the engine over. Either method allows moving the timing chain for inspection. A magic marker or nail polish paint can be applied on the chain link plates so you can gauge how far the chain moves. Wipe off oil before applying magic marker or paint spots.

I too do not think the timing chain is stretched or damaged. If you believe the timing chain is damaged, put plugs back in, connect plug wires and startup. A cold engine will idle higher until it warms up but you only need to run the engine less than a minute to listen for chain noises. Some oil will spatter, to be expected with the valve cover off.

can0fspam 01-08-2020 04:40 PM

Re: Unknown engine noise when cold
I pushed up and down on the length of chain visible between the cam gears.
I was barely able to move it in either direction -- it was almost unnoticeable.
I always try really hard to diagnose noises because i pick up on them easily. I am not worried about anything going bad at the moment -- but i am prepared for the worst.

The saturn needs an oil change soon so i will try running a quart? of ATF before draining and maybe adding a zinc additive with fresh oil.

toggenburg 01-08-2020 05:38 PM

Re: Unknown engine noise when cold
I also pour in a full quart of ATF in each oil change on all cars since the 1970's.
It won't hurt a thing, but it will clean up an engine, better and cheaper than Marvel Mystery oil, or Rislone products. Never had any engine opened up for any reason yet. That's on many engines and cumulative mileage easily of over 1M miles. It won't hurt your engine to keep ATF in the oil year round.

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