Jeep has whistling noise under the hood

[Donald]

Its more noticeable when its cold. First I thought it was a vacuum hose that was leaking. A slight change in RPM will make it go away.

Now it sounds like it is or is near the alternator. Not a squeal, and not a bearing grinding noise, but a whistle.

Jeep 4.0 engine.

 

[old1]

Belt??

 

[Lyman]

Brake boosters going bad are a common on these. I just had to do mine because it was whistling at me.

 

[Olas]

A wooden spoon is your friend

 

[SwampSurvivor]

The alternator is getting tired. Chrysler alternators seem to really whistle when they are tired or being overworked.

 

[whaleinafishbowl]

A supercharger like whistle is usually the fan clutch.

 

[Donald]

Originally Posted By: whaleinafishbowl
A supercharger like whistle is usually the fan clutch.


I believe its got an electric fan.

 

[Pop_Rivit]

Just take your mechanics stethoscope (or a screw driver if you don't have one) and find out where the noise originates. Once you do that, it should be pretty easy to figure out the cause.

 

[440Magnum]

Originally Posted By: Donald
Its more noticeable when its cold. First I thought it was a vacuum hose that was leaking. A slight change in RPM will make it go away.

Now it sounds like it is or is near the alternator. Not a squeal, and not a bearing grinding noise, but a whistle.

Jeep 4.0 engine.


Probably IS the alternator. Its a Nippondenso, so nothing special about it and they generally last a LONG time, so it may not acutally be a problem. It could be the belt making a noise at the alternator pulley due to temp/humidity changes, too. The alternator is the fastest-spinning thing driven by the serpentine belt, so it tends to make the highest pitched whine.

Does the whistle change when you turn the headlamps or rear defogger or some other heavy load on or off? If so my bet would be a belt noise.

 

[anonobomber]

Probably the idle air control valve. Your Jeep has almost the same one my Dodge truck has with the 5.2 motor and the idle air control valve is always pretty whistly when it is cold.

 

[KCJeep]

Mine did the exact same thing this last winter when started cold and the temp was just right. I also assumed it was a vacuum leak. Had not gotten around to looking into it further.

I would not have thought an alternator could make such a whistle. Interesting.

 

[yvon_la]

Alternator can make a ruckus. Not adnormal. Most mechanic wont notice.check wiring for induction. Basicly nothing steel should be within an inch of any wire. Get pine cone zip tie holder the go where screw hole are avail. Plastic is your friend. Lastly check battery. Charge it.: SLOWLY.. This is my diagnostic wthout knowing exactly where the noise come from Precisely

 

[Kawiguy454]

I recently had a whistle/whirring that went away when revved. Suspected vacuum leak or alternator bearings. Take off the belt and spin the spinny things you should be able to feel which one is off note.

Turned out to be the idler pulley bearings. Ordered new Canadian made Gates pulley and belt and purrs like a kitten again.

 

[JHZR2]

Originally Posted By: 440Magnum
Originally Posted By: Donald
Its more noticeable when its cold. First I thought it was a vacuum hose that was leaking. A slight change in RPM will make it go away.

Now it sounds like it is or is near the alternator. Not a squeal, and not a bearing grinding noise, but a whistle.

Jeep 4.0 engine.


Probably IS the alternator. Its a Nippondenso, so nothing special about it and they generally last a LONG time, so it may not acutally be a problem. It could be the belt making a noise at the alternator pulley due to temp/humidity changes, too. The alternator is the fastest-spinning thing driven by the serpentine belt, so it tends to make the highest pitched whine.

Does the whistle change when you turn the headlamps or rear defogger or some other heavy load on or off? If so my bet would be a belt noise.




+1

I've heard alternators that make a faint whistle/whine under changing rpm. I've also seen poor enough quality of "quality" rebuilds that I'd probably leave alone...

 

[HM12460]

Originally Posted By: anonobomber
Probably the idle air control valve. Your Jeep has almost the same one my Dodge truck has with the 5.2 motor and the idle air control valve is always pretty whistly when it is cold.




Yes. My now gone 2 weeks ago 2003 Dakota did that too. It was much more noticeable in the winter time. It would stop if you let up on the gas pedal.

 

[Kruse]

You may have found your problem by now, but if not, check the vapor canister purge valve. I've got three 4.0 Jeeps from the late 90s era and I've heard the vapor canister purge valve vibrating on on each of them on a cold morning. It goes away after the engine warms up. OEM has the best quality, but pictures of the replacement valves are shown on RockAuto.

 

[Nick1994]

My mom's 2012 Jeep Patriot just got the alternator replaced this week at the dealer, it had a whining noise while driving and they said it had bad bearings. I haven't driven the car yet to see if it still has the noise. Something to look into definitely.

Pop off the serpentine belt and spin everything, then start it and see if the sound is there with the belt off for just a second, belt runs the water pump so don't run it real long.

 

[Olas]

Originally Posted By: Pop_Rivit
Just take your mechanics stethoscope (or a screw driver if you don't have one) and find out where the noise originates. Once you do that, it should be pretty easy to figure out the cause.


Originally Posted By: Olas
A wooden spoon is your friend