Engine noise during warmup

[enslow]

For the last few years I noticed my wife's 97 Lesabre was rather noisy while warming up. It was mainly engine noise, not knocking. I cannot rule out all vacuum leaks, although I have already replaced a number of the hoses. I remember reading either here or on another forum that some have complained about engine noise during the warm up as well. Some have it, some don't.

I recently discovered that I had some very slight exhaust manifold leaks. Not enough to smell exhaust, but enough I could feel a slight breeze on my hand when I held it in certain areas by the manifold. (And, no, it wasn't the fan). I tightened the exhaust manifold bolts and the engine is quieter now. All I have to do is get rid of the power steering whine and an alternator chatter.

Some have blamed the IAC, vacuum leaks, etc. Those are possible sources of noise. I'm posting this because if you have engine noise during warmup, you may wish to try tightening your manifold bolts about 1/16 of a turn. Also make sure the donut gaskets at the crossover are sealing too.

[Tech II]

They are known for the exhaust "doughnut" between the manifold and the exhaust pipe coming apart, and creating a noise......

[edwinn]

Originally Posted by enslow

For the last few years I noticed my wife's 97 Lesabre was rather noisy while warming up. It was mainly engine noise, not knocking. I cannot rule out all vacuum leaks, although I have already replaced a number of the hoses. I remember reading either here or on another forum that some have complained about engine noise during the warm up as well. Some have it, some don't.

I've had a grinding-sucking noise in my Riviera 3800 engine during warm-up in COLD weather ever since purchasing it in 1998. It's understood to be a passage in the intake/throttle body that functions as a choke or fuel enrichment circuit? {cannot remember the correct terms} and was told that it's normal. It sounds like running a knife around inside an empty glass mayo jar of slightly more noisy!


-Ed

[enslow]

I've done some further looking into the issue. The problem is definitly with the exhaust manifold. I stuck a vacuum on the blower mode through the exhaust pipe and felt around the exhaust manifolds as best I could. I still felt air coming out from the manifold right near the #5 cylinder. I tightened the manifold bolt a little more and I think I stopped the leak, and the engine is a fair bit quieter.

I had trouble with the donut gasket before, but this is definitly the exhaust manifold. I can't fit my hand in around the rear manifold from above, but I wouldn't be suprised if the rear had a leak too. I suppose both manifolds should be changed soon.

Ed, you may wish to look at your exhaust manifolds too. I thought it was a vacuum leak at the intake for over a year, because that's exactly what it sounded like. Turns out I was wrong.

[edwinn]

Originally Posted by enslow

I've done some further looking into the issue. The problem is definitely with the exhaust manifold. I stuck a vacuum on the blower mode through the exhaust pipe and felt around the exhaust manifolds as best I could. I still felt air coming out from the manifold right near the #5 cylinder. I tightened the manifold bolt a little more and I think I stopped the leak, and the engine is a fair bit quieter.

I had trouble with the donut gasket before, but this is definitely the exhaust manifold. I can't fit my hand in around the rear manifold from above, but I wouldn't be surprised if the rear had a leak too. I suppose both manifolds should be changed soon.

Ed, you may wish to look at your exhaust manifolds too. I thought it was a vacuum leak at the intake for over a year, because that's exactly what it sounded like. Turns out I was wrong.

This is a revelation, because the Buick dealer who "found" the lo-miles Riv for me said the noise, which was VERY prominent in winter weather, was the intake system. Not easy to diagnose because you only have a few mins in COLD weather to find the problem.

I'll state it again.. the noise is described as "running a table knife around inside an empty glass mayo jar" and there's a "clanking" or grinding component to the sound as well, almost like very rapid drumstick tips. It goes away in a few minutes. I've lived with this for 15 years and have normalized it.

Concerning the manifolds.. are you talking about where they bolt to the heads? Wouldn't there be evidence of a leak with black soot or carbon deposits nearby?


-Ed

[Tech II]

Sure you are not confusing the noise with the air pump?

The air pump comes on, on a cold engine....the length of time is determined by the startup temp of the coolant.....

[enslow]

Ed,

I suppose there would be a black spot, although the newer cars burn far more completely than the cars of 25 years ago. Keep in mind I'm looking from above so I cannot actually see the spot, just feel it when I reach in there.

Your noise could be intake, but it could be worth checking the exhaust manifolds. They head up within a minute. I know that sometimes when the dealership doesn't know, they will feed you a line to answer your question. These lines usually come from the "service advisor", not the actual mechanic that works on your car because the mechanic is often conveniently hidden behind the service techs. (Nothing bad against the mechanics, more a comment about the dealership structure.

[enslow]

Originally Posted by Tech II

Sure you are not confusing the noise with the air pump?

The air pump comes on, on a cold engine....the length of time is determined by the startup temp of the coolant.....

Could be on Ed, but not mine. I have no air suspension, and I have confirmed it is leaking at the exhaust manifold.

I am considering changing the front exhaust manifold. Is it worth considering the Dorman? Should I get GM? If I get Dorman, they come with manifold gaskets. GM didn't use gaskets at the factory, and doesn't supply gaskets with their manifolds.

[HotZ28]

Originally Posted by enslow

Could be on Ed, but not mine. I have no air suspension, and I have confirmed it is leaking at the exhaust manifold.

I think what TechII was referring to was an air pump on the engine, which neither of these have. Obviously, the rear air ride compressor has nothing to do with engine start up temp.

I am considering changing the front exhaust manifold. Is it worth considering the Dorman? Should I get GM? If I get Dorman, they come with manifold gaskets. GM didn't use gaskets at the factory, and doesn't supply gaskets with their manifolds.

Gaskets make imperfections such as warping and uneven surfaces more forgiving, hence the use of header gaskets when used in conjunction with tube headers. I would not hesitate to try Dorman for this purpose, especially if cost is a factor.

[edwinn]

Originally Posted by enslow

Could be on Ed, but not mine. I have no air suspension, and I have confirmed it is leaking at the exhaust manifold.

I am considering changing the front exhaust manifold. Is it worth considering the Dorman? Should I get GM? If I get Dorman, they come with manifold gaskets. GM didn't use gaskets at the factory, and doesn't supply gaskets with their manifolds.

Had normalized the issue and dismissed it, but now since the topic came up.. am hearing the grinding clatter sound on start-up, in the garage in August. Not a cold weather issue (although it's worse in cold weather) but a cold engine issue. It's more prominent with the hood open, and definitely not the air suspension pump. Haven't seen a manifold air injection pump since the 350 CI V8 engines.

The sound (once more) is described as "a blunt dinner knife running around inside an glass mayo jar" together with "screws clattering in a coffee can" and a "drumstick 'tipity-tipity' component." So there's a grinding, clatter and rapping component all combined. It's rather loud, yes!!

I still think if there was exhaust leaking then you'd have a soot residue. Have we dismissed the air induction/cold engine/choke explanation? That's what the dealer told me who diagnosed it. Let's get this one figure it out.


-Ed


Edit: tell you what... I'll endeavor to make a hi-def video of this in stereo, mounting the PowerShot camera on a tripod aimed at the engine compartment and start 'er up.

[enslow]

You may not be able to see the soot. I certainly didn't notice any. If the exhaust leak is on the underside (like mine), you'll be hard pressed to see the soot. The easiest way to find it is to use a smoke machine (which I don't have) or try a shop vac on blower mode through the exhaust tail pipe, then feel around. Mine was quite hard to find. I didn't feel any air rushing for a minute using the shop vac trick. It could only be felt from one angle. A smoke machine would definitely be better.

[edwinn]

Originally Posted by enslow

You may not be able to see the soot. I certainly didn't notice any. If the exhaust leak is on the underside (like mine), you'll be hard pressed to see the soot. The easiest way to find it is to use a smoke machine (which I don't have) or try a shop vac on blower mode through the exhaust tail pipe, then feel around. Mine was quite hard to find. I didn't feel any air rushing for a minute using the shop vac trick. It could only be felt from one angle. A smoke machine would definitely be better.

Anything new on this topic? Would like to get more feedback / input from GM guys or dealer Techs that it's a known issue. I'm more sensitive to the nosie now and noticing the "clatter" at each start-up, even in summer weather. It will be WORSE in cold weather.

-Ed

[Tech II]

An old trick to find ex manifold leaks, was to remove a couple plugs(one on each bank) and add a few drops of oil in the cylinders...replace plugs and start the car.....smoke would come out where the leak was....

[HotZ28]

Originally Posted by edwinn

Had normalized the issue and dismissed it, but now since the topic came up.. am hearing the grinding clatter sound on start-up, in the garage in August. Not a cold weather issue (although it's worse in cold weather) but a cold engine issue. It's more prominent with the hood open, and definitely not the air suspension pump. Haven't seen a manifold air injection pump since the 350 CI V8 engines.

The sound (once more) is described as "a blunt dinner knife running around inside an empty glass mayo jar with" together with "screws clattering inside a coffee can," and a "drumstick tip 'rapity-rapity' component." So there's a grinding, clatter and rapping component all combined. It's rather loud, yes!!

I still think if there was exhaust leaking then you'd have a soot residue. Have we dismissed the air induction/cold engine/choke explanation? That's what the dealer told me who diagnosed it. Let's get this one figure it out.


-Ed


Edit: tell you what... I'll endeavor to make a hi-def video of this in stereo, mounting the PowerShot camera on a tripod aimed at the engine compartment and start 'er up.

Ed, do you have a supercharger coupling clatter? Take the S/C belt off and check for back/forth play in the snout coupling.

[edwinn]

Originally Posted by Edwinn

Tell you what... I'll endeavor to make a hi-def video of this in stereo, mounting the PowerShot camera on a tripod aimed at the engine compartment and start 'er up.

Originally Posted by HotZ28

Ed, do you have a supercharger coupling clatter? Take the S/C belt off and check for back/forth play in the snout coupling.

No sir, it's a L36 engine with a single accessory belt. The two explanations I have are:

1) Induction/intake noise with cold engine - worse in winter,

2) Exhaust leak with cold engine.

It's a clatter all right.
See post above where I've clarified the description of the sound (with underlines.)


-Ed