Loud Squeal Engine

RavenMocker

Well-known member
Jul 25, 2015
45
4
PNW
2000 Discovery 4.0 with almost 157K. There is a loud squeal coming from the engine somewhere. It sounds like from the left hand side towards mid to rear engine. It is some what intermittent and fluctuates during idle or it can remain constant. Same issue when driving and when you reach road speeds then left off the gas pedal so you stay at the posted speed. It goes away when you rev the motor or during acceleration at any rpm. It just totally disappears but comes back after you let off the gas pedal. The sound is similar to hearing a bearing going out on a pulley although much louder. As soon as you give the engine a little gas the noise goes away. The noise was going on before I did the work on my truck which I listed in another post.

Things I've done to troubleshoot.
- Re-torqued the intake manifold. As always in a proper sequence and specs. (Still Squeals)
- Removed the serpentine belt to test everything on the front of the engine. (Still Squeals)
- Sprayed carb/intake cleaner around the gasket of the intake manifold and the RPM remained the same. Didn't drop nor increase.
- Sprayed carb/intake cleaner around the throttle body, all vacuum hoses, the SAI, around the heads, Everyplace I could think of with a vacuum. No decrease/increase of rpm.
- All coolant and oil levels are good with no mixture. There are no leaks from either.
- A few years ago on another truck I had a champion spark plug pop a hole in the ceramic and made a somewhat similar noise. When you looked at the plug it looked normal. But it was leaking. So I checked them and they seem fine on both sides of the engine.

Zero issues with starting the engine. It has always started and ran great. The transmission works as it should. I thought maybe the torque converter or pump but then again the transmission works great.
Bad lifter? I would think the noise would get louder with rpm. Wouldn't it just get louder with rpm? Maybe it pumping up at higher rpm gets rid the noise?

Ok that's what I've checked into. I did the internet search and no cigar. I could use some help. Appreciate any.
 

boxster

Well-known member
Jun 1, 2009
253
31
Fallbrook Ca.
Do you have a mechanics stethoscope or a length of hose to listen and isolate the noise? You mentioned the noise is still there after removing the belt, is it a air noise or a metallic noise? Also is it louder when at idle? I assume you have help listening to isolate the noise.
 

Blue

Well-known member
Mar 26, 2004
9,511
538
AZ
With the serp belt off and no accessories running it still squeals?
 

RavenMocker

Well-known member
Jul 25, 2015
45
4
PNW
With the serpentine belt off it still squeals. When you rev the engine up the noise is eliminated. But as soon as you let off the gas pedal it starts to squeal again. Its only squealing when at idle. The sound is like when a persons fan belt needs to be replaced minus the oscillation. Or a bearing going bad. It’s pretty loud too. Otherwise the engine starts fine and runs fine. I’ll pull codes as soon as my tablet gets fully charged.
I had a stethoscope but I found it broken. Looks like a new one is in order.
 

discostew

Well-known member
Sep 14, 2010
6,774
649
Northern Illinois
I bet it’s a vacuum leak. It doesn’t happen often but sometimes the leaks just right. Makes a hell of a whistle.
Get a spray bottle and fill it with water. Turn the nozzle till it’s a stream of water like a squirt gun. Spray the shit at your intake gasket areas. Both upper and lower. Don’t skimp on the water. You want to fill that leaking area with water and it will stop whistling until it pulls all that water thru.
 
Last edited:
  • Like
Reactions: RavenMocker

RavenMocker

Well-known member
Jul 25, 2015
45
4
PNW
I bet it’s a vacuum leak. It doesn’t happen often but sometimes the leaks just right. Makes a hell of a whistle.
Get a spray bottle and fill it with water. Turn the nozzle till it’s a dream of water like a squirt gun. Spray the shit at your intake gasket areas. Both upper and lower. Don’t skimp on the water. You want to fill that leaking area with water and it will stop whistling until it pulls all that water thru.

Thank you! Thats another tool in the bag of tricks for troubleshooting. I will try this later today. Ive always just used the spray carb cleaner until a change in rpm. Ill report back with my findings. Now that my tablet is charged I can pull codes and watch sensor outputs.
 

RavenMocker

Well-known member
Jul 25, 2015
45
4
PNW
I bet it’s a vacuum leak. It doesn’t happen often but sometimes the leaks just right. Makes a hell of a whistle.
Get a spray bottle and fill it with water. Turn the nozzle till it’s a dream of water like a squirt gun. Spray the shit at your intake gasket areas. Both upper and lower. Don’t skimp on the water. You want to fill that leaking area with water and it will stop whistling until it pulls all that water thru.

Ok I followed your advice and it worked. Front intake gasket. Time to take the intake off, clean, and install it again.
 
  • Like
Reactions: Spark6

discostew

Well-known member
Sep 14, 2010
6,774
649
Northern Illinois
Awsome. One thing to think aabout if your doing the lower intake. The end clamps can get in the way of the intake fully seating. If you torque the end clamps before you do the first torque on intake bolts, it can interfere with the intake manifold. We also used to grind a little off both ends of the endclamps to make sure manifold didn't contact it.