4.0L suddenly very loud - JeepForum.com
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post #1 of 8 Old 05-17-2011, 08:59 AM Thread Starter
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2002 WJ 
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4.0L suddenly very loud

I haven't had my Jeep for very long so I'm new to this world, but I've noticed the engine suddenly got very loud. It's a stock 2002 Grand Cherokee Limited w/a 4.0L inline six w/175,000 miles on it. No codes are being thrown. I'm wondering if it has something to do with the fan. I noticed while driving on the highway on a 70-degree day that there was a strange "hiss" (almost like an electrical sound...kinda' sounded like when you barely open a pressurized bottle of soda) and then it suddenly got really loud - even at cruising speeds I could notice the difference in sound. It's not overheating - staying consistently to the left of 210-degrees. I got home and put it in the garage. The next day, I went out to turn it on to see if it still sounded loud and I noticed the fan was on - like "on" hard enough to create wind in the engine bay. I thought that was odd too since it had sat for over 12 hours in a 60-degree garage. It's not idling rough, no knocks, pings, etc. Just significant HP loss and a loud roar @ W.O.T. Thanks in advance!

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post #2 of 8 Old 05-17-2011, 11:44 AM
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I'm assuming it's a mechanical fan? If so, sounds like the fan clutch is bad and locked up.

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post #3 of 8 Old 05-17-2011, 11:59 AM
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When i start My WJ up either hot or Cold it sometimes sounds like a leafblower, hard to explain this but i Will try My best.

Yeah like a leafblower/big fan loud sound, dosnt happens every time but seems to happen more often due to outside temp. More in summer, almost never in vinter.

When it is like this, its seems like it revs up and dont have the power, but still driveble.

Its like this on idle and when i start to drive, after a couple of 100 meters its suddenly goes away and it act normal again.
It only apears when i start it up and never wile driving.

This come and goes and i Really cant understand it because when it dosnt happens or Go away everything is normal.
Only thing i can say i noticed is That it seems to be affected by outside temp.

This is What happend to mine surch My, wj acting weird thread, There you can read about the fan clutch, How to check That out.
Havent fixd mine yet but they say its easy and cost about 55$ for the part.

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post #4 of 8 Old 05-17-2011, 12:04 PM
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sounds like an intake leak to me, maybe the manifold gasket? take some carb cleaner or any other similar spray and spray it near the intake manifold (not directly at the air intake)...if the idle goes up thats what it is.

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post #5 of 8 Old 05-17-2011, 12:58 PM Thread Starter
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I went out and popped the hood and before starting it or anything, tried to spin the fan by hand (gently) and got maybe an 1/8 of a turn from it before I hit resistance (both directions). So, I got in and started it up and the airplane noise was gone. Drove it home watching the temp gauge the whole time and never went past 210 (even saw where the thermo opened up and temp dropped) and still no loud noise. Didn't think to check it when it was hot though but I ended up leaving it at home since I could hear a cyclic metallic scraping sound kinda' like I bent a blade (hoping that's not the case).
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post #6 of 8 Old 05-18-2011, 09:38 AM Thread Starter
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Update: Replaced the clutch and voila! Airplane noise is gone.
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post #7 of 8 Old 05-18-2011, 09:55 AM
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glad to hear everything is all set! my 01 WJ has the towing package with mech fan. when i start it the fan is typically engaged and then disengages a few hundred feet down the road from my driveway. i have never had any over-heating issues with the vehicle at all even in the most extreme conditions so i assume all is well. prob have to change the fan clutch anyway though.

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post #8 of 8 Old 05-19-2011, 08:15 AM Thread Starter
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My new one is the same way. From what I've read it has heat activated fluid that causes the fan to engage/disengage. It starts off loud but once I can see the gauge is close to 210, the thermo opens and the engine quiets down. Hasn't gone past 210 yet (knock on wood).
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