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Unread 04-07-2008, 10:20 AM   #1
speedbird1229
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Weird engine sound when cold (spark plugs?)

Hey!

Recently I've began to notice that when the Jeep has been stopped overnight or for just a longer period, the engine will sound inside much louder and abnormal when I rev it above idle. I'd compare the sound to an old Volvo diesel car which always sound terrible. My sound goes normal just after a few minutes of driving or today when I had more time, I kept the RPM in neutral gear at about 2000 and suddenly it just switched over to normal sound. The RPM also wanted to swing about +/- 500 units while the sound was bad. RPM stopped swinging with the sound change.

I thought that perhaps one or some of the spark plugs are dirty or on their way out? It seems exactly like after a few minutes the plug cleans itself out or something and starts working properly. I haven't changed the plugs yet, they could be quite old on it.

Thanks!

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Unread 04-07-2008, 01:46 PM   #2
tbm5690
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This happened with my buddy's WJ...I believe it was a cracked manifold but I'll check up on that
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Unread 04-07-2008, 01:57 PM   #3
CMARJEEP
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its the mechanical cooling fan... once you start driving it kicks off. its normal. the thing you want to watch for is when it is always sounds like that even when its warm. when that happens the fan clutch has gone bad. but for a minute or two on a cold morning that is normal. mine does that until i drive a block or two after i leave it out on a cold night.
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Last edited by CMARJEEP; 04-08-2008 at 01:20 AM..
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Unread 04-07-2008, 02:04 PM   #4
tbm5690
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I don't think his is hydraulic, though?
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Unread 04-07-2008, 02:09 PM   #5
CMARJEEP
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i think ZJ's came with mechanical fans. im not 100% sure. but his description sounds exactly like the fan.
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Last edited by CMARJEEP; 04-08-2008 at 01:20 AM..
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Unread 04-07-2008, 02:15 PM   #6
JG_Canuck
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Quote:
Originally Posted by CMARJEEP View Post
i think ZJ's came with hydraulic fans. im not 100% sure. but his description sounds exactly like the fan.
I was thinking exactly the same thing...
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Unread 04-07-2008, 02:32 PM   #7
alexo1us
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He discribed as a diesel sound.
but for the record zj did not have hydrolic fans 5.9 had electric the rest were belt driven
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Unread 04-07-2008, 02:41 PM   #8
Windowsrookie
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It's the fan. Completely normal, the fan clutch is full of fluid that needs to warm up.
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Unread 04-07-2008, 04:28 PM   #9
alexo1us
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if it is a roar he is talking about then yes the fan
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Unread 04-08-2008, 01:03 AM   #10
speedbird1229
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Thanks for all the answers. Never thought this was the case! Yes it's kinda like a roar, if I have time I will try to record it with video camera just to be sure. So the fan is belt driven I believe but what does the fan clutch exactly do? How does it work?
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Unread 04-08-2008, 01:13 AM   #11
CMARJEEP
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it engages when the jeep comes to an idle to provide more airflow. but as soon as you start accelerating the clutch will disengage and the fan will stop spinning because air is now naturally flowing through the grill so the fan is not needed anymore. when the clutch goes bad it will always be engaged and will always be spinning which is what will give you the roar. or it will not spin at all and will overheat when you come to stops....
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Unread 04-10-2008, 10:30 AM   #12
speedbird1229
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I see. Thanks, will keep my eyes on it just in case...
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Unread 04-10-2008, 11:02 AM   #13
98ZJ_USMC
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I was wondering about the same thing. My 98 does this in the cold. Makes sense.
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Unread 04-10-2008, 05:30 PM   #14
JKot55
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I always wondered that too. Thought it had to do with the transmission but never looked into it. Thanks!!
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Unread 04-11-2008, 01:16 AM   #15
speedbird1229
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But if a spark plug went out, how do you notice it on a V8 engine? Does it add vibrations or loose a lot of power?
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