What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

What's an exhaust leak sound like?

dremu

dremu

Officious Thread Derailer
GMOTM Winner
Joined
Feb 27, 2000
Posts
16,370
Reaction score
1,128
Location
East of San Francisco
I'm chasing a mystery noise in my truck that might be an exhaust leak, but I'll be damned if I can locate it.

The really annoying part is that it doesn't occur at idle, or at least is much quieter. Only off idle (under load) does it get noticeable.

The scary thing is that it reminds me of the fweem that air cooled VW's make, which makes me wonder if it's valve clatter or pinging. I swear the timing is good so I don't *think* it's detonation. Base timing is 8* and total timing at ~3000RPM is maybe 30*, which if anything is too little advance, but it's a stock motor... I digress.

If it was valve clatter, would I hear that more once the secondaries on the Q-jet open up or something? :dunno:

I've tried running about with my mechanic's stethoscope, but since it really only happens while driving it's hard to nail down.

I also tried recording it on my phone and the damn auto-volume-level means I just end up with recordings of road noise and my hairy legs. :(

Any thoughts as to possible causes, diagnostic methods, whatever -- let's hear 'em!

-- A
 
Exhaust leak sounds like a heavy lifter tick, only under load. If the leak has been around for a little while you can usually find where it's coming from visually...a little blackened around where it's leaking from.
 
^What he said. In really extreme cases, I've hooked up an air hose to the cylinders and used a piece of paper with one end cut up (to form tiny little fingers that will wave when air hits it) to find it. Most of the time it's the manifold/header gasket. Or if you still have manifolds, it might be cracked. Pretty common.
 
The noise could be coming from your hairy legs.


-G
 
It sounds like ticking or spitting and you usually only hear it under load. If you hear it about once for every 2 revolutions, it's probably one cylinder leaking at the manifold. The rear bolts love to come loose so that #7 or #8 is making noise. If it sounds more like twice for every revolution, that's likely the donut gasket (or collector). Sometimes you can feel the leak by putting your hand close to every joint (at idle). Better yet is an open hose stethoscope. The little bit of wind across the open tube is quite loud. A piece of hose to the ear will work if you don't have a stethoscope.

The more fun way to find leaks is letting the engine suck in seafoam. When the smoke screen starts you can usually see some coming from the leak. I've also heard of running a lit candle all over the exhaust to look for the flame flickering, but it seems like a lot of places would be hard to reach.
 
Greg72 said:
The noise could be coming from your hairy legs.


-G
Click to expand...

At least I have hair. Some. :doah:

I'm feeling a bit of relief that exhaust leaks are more audible under load, so it's less likely that the motor is somehow about to explode. (Because that would Might As Well morph into a big block transplant :haha: )

I'll see if I can locate it with a stetho-hose-scope.

Thanks all!

-- A
 
Last edited:
I have had multiple exaust leaks on the old crap we have bought and resurrected. I find before wasting to much time trying to find it physically I just replace the manifold to pipe donuts and it fixes it 75% of the time. I think it is a total of $5-8 bucks for them and can be 10 min to 3 hours to replace (depending on crust and how frozen the bolts are). I some times save the trip and get new exaust bolts to.

Once you have that done then you can start sourcing the pinhole rust spot if the problem keeps up. Luckily we don't live in rust belt regions where you start with the donut and replace every thing behind it.:D:haha:
 
dremu said:
At least I have hair. Some. :doah:

I'm feeling a bit of relief that exhaust leaks are more audible under load, so it's less likely that the motor is somehow about to explode. (Because that would Might As Well morph into a big block transplant :haha: )

I'll see if I can locate it with a stetho-hose-scope.

Thanks all!

-- A
Click to expand...


I have only two more ideas for you:

1. Ratchet strap yourself tightly to the underside of the truck just below the exhaust and have a friend drive slowly around the neighborhood while you look and listen for noises/leaks. This is a good one, but only really works while the engine and exhaust are relatively cold.

2. Lay in the engine compartment with the hood open. Bungee cord your iPhone to the front core support.... then have your friend do a "FaceTime" call to you while they sit in the driver's seat. This way, they will still be able to drive with the hood open and see the road. PLUS, they can also listen to your girlish screams for help while they drive you around... or possibly even offer a second opinion on any odd noises you locate.


You're welcome.



-G
 
Greg72 said:
I have only two more ideas for you:

1. Ratchet strap yourself tightly to the underside of the truck just below the exhaust and have a friend drive slowly around the neighborhood while you look and listen for noises/leaks. This is a good one, but only really works while the engine and exhaust are relatively cold.

2. Lay in the engine compartment with the hood open. Bungee cord your iPhone to the front core support.... then have your friend do a "FaceTime" call to you while they sit in the driver's seat. This way, they will still be able to drive with the hood open and see the road. PLUS, they can also listen to your girlish screams for help while they drive you around... or possibly even offer a second opinion on any odd noises you locate.


You're welcome.



-G
Click to expand...

There would be many odd noises during either of these events. While they might start with that most greatest of man phrases, "Hey y'all, watch this!" they would likely end in that most depressing of sounds, "Whirrrrrrrrr bip bip", followed by "What's the problem, officer?"

However, I am now thinking about engine burritos. Gives me a good excuse to fix the leak :D

-- A
 
The "smoke test" often works well...do it after a cold start,as sometimes a cracked exhaust manifold will "seal" itself up after it warmed up and expanded after running it awhile...you should see the smoke escaping from any suspect areas..

I've seen garages use an emission tester probe to detect the unburned hydrocarbons the exhaust leak lets escape too..

I used a piece of 1/4" vacuum hose in my ear to pinpoint a "leak" the other day on a friends Ford Ranger he'd bought used recently..sounded like a loose spark plug--turned out someone evidently stripped the plug hole and used a heli-coil,and it wasn't installed all the way fully,and he had to buy another heli-coil insert and install it..leak corrected!..

By the way,I nearly got myself electrocuted using that hose to pinpoint the noise--while I was probing with the hose around the spark plug hole to find the source of the "fft-fft-fft" noises,I found out the hard way the carbon black in rubber hose makes a dam good conductor of the 20,000+ volts the coil provides to fire the spark plug!..you haven't lived till that kind of voltage ZAPS you right in the ear drum,direct to your brain!..:eek1:
 
diesel4me said:
By the way,I nearly got myself electrocuted using that hose to pinpoint the noise--while I was probing with the hose around the spark plug hole to find the source of the "fft-fft-fft" noises,I found out the hard way the carbon black in rubber hose makes a dam good conductor of the 20,000+ volts the coil provides to fire the spark plug!..you haven't lived till that kind of voltage ZAPS you right in the ear drum,direct to your brain!..:eek1:
Click to expand...

I'll go and listen to the spark plugs.

But, umm, I am SOOO tempted to response to your electrocution story with "This would explain a few things" ... :doah:

I've only ever zapped myself with 110 and rarely 220. Higher than that is bad for the ... well, everything.

-- A
 
I'm just glad the Ranger doesn't have HEI with a 50,000 volt coil --I've had a bad plug wire on one of my Gm's zap me good,one day when it was raining my engine started skipping,I ran my hand along the plug wires where they went under the air cleaner and I got jolted good when I found a spot that rubbed thru on one wire..--the spark went up my arm,thru my torso,and used my penis for a ground rod,to the zipper on my jeans,then to ground the spark to the front fender..THAT HURT!..:eek1:..felt like someone stuck an ice pick in my nut sack for hours afterwards..

Luckily an ignition system doesn't produce much amperage,thats what'll kill you--but some people have died after getting zapped by an HEI system,who had heart troubles or were exceptionally sensitive to electrical shocks..
I had a friend who "tested" house wires for current by using 2 fingers--he'd just feel a good tingle--me,I put a 9 volt battery to my tounge to see if its "good" and it'll knock me on my a$$!..
 
You must log in or register to reply here.

Latest Posts

Top Bottom