3.7L Knocking when cold

SD-KJ · **Posted:** Sun Nov 21, 2010 12:27 am

Ok, another one for you next gen guys.. my old 2002 kj with the 3.7 would knock on start up and for a bit when cold but it seems my new one does it more.. could be just my imagination but is this something i need to have the dealer address? I'm having some trouble wrapping my brain around some of these stupid little issues that i don't think should be happening on a current year model jeep with 17k on it...

nightdrv · **Posted:** Sun Nov 21, 2010 12:51 am

Mine does it too. Been slowly getting louder since 20k or so. I change my oil frequently, use good filters, good quality gas, etc. No improvement. It's a bummer that my warranty is up in like 500 miles... 'cause you know that when it's finally up it'll happen.

Marlon_JBT · **Posted:** Sun Nov 21, 2010 1:36 pm

Mine does it too. No concern.

jon153 · **Posted:** Mon Nov 22, 2010 3:07 am

It's hard to say what it is without actually being there and hearing it. One thing you may want to check is the main bearings on the crankshaft. They can make a knocking noise on start up if they are going bad. I also wouldn't look at the mileage as a factor in excluding this because it's possible that some bad ones could have come from the supplier. If your warranty is almost up I would definitely be heading over to the dealer to make a complaint about the noise. Leave it with them if you have to so they can crank it up cold if they need to. Better to get it documented now than try to get something done after the warranty expires. You will have better legal standing if something happens and they can pull it up in their computer and say, "Hey, you did complain about that back in November!".

SD-KJ · **Posted:** Mon Nov 22, 2010 10:40 am

I heard it again this morning and I'm starting to think my issue is not the knocking i'm used to. This is more of a intermittent knock, i'm planning to get an oil change here in the next month or so, i will have the dealer look at it then.

Marlon_JBT · **Posted:** Sat Nov 27, 2010 4:35 am

UPDATE: I haven't heard it all week?

Amazing. Cold start, warm start, no knocking at all. Maybe you're right SD, it's an intermittent issue. I'm still not worried about it because IMO it sounds like the typical 3.7L startup knock.

At The Helm · **Posted:** Sat Nov 27, 2010 12:37 pm

Mine does it all the time upon initial morning startup.

tools113 · **Posted:** Sun Nov 28, 2010 12:08 am

could actually be your injectors.

ups4 · **Posted:** Sun Nov 28, 2010 6:15 pm

What is this "cold morning" you speak of?

If it gets below 70 here, it's cold

Paul

JojosJeep · **Posted:** Mon Dec 06, 2010 8:43 am

Mine does it too, seems kind of random but had become more frequent so I brought it in before my 36k was up and they said they couldn't reproduce it....whatever...but it was normal for a 3.7. I don't like that answer. He said he recommended changing the plugs, they could do it for around $140 :-)r

My husband took care of it this weekend and so far it is running a lot smoother and it's been around 20F in the morning.

Maxxis · **Posted:** Mon Dec 20, 2010 12:44 am

I just found this forum. I have a 2011 KK 4x4. And I've noticed this noise myself. I picked up the Liberty with only 10 miles on it. And I didn't notice it until I had about 150-200 miles on it. I'm taking it to the dealership this week to have it looked at.

Serge A. Storms · **Posted:** Thu Dec 23, 2010 12:01 am

My 2011 (4200 miles) does it too, seems to quiet a bit after a half minute or so but still makes some noise. One of the Tech Advisors for MOPAR tells me its normal injector noise. I am currently on assignment at a dealer, maybe I will start a couple on their lot to see what they sound like.

BTW, Cool forum, I have read a bunch of useful info. Glad I found it!

tjkj2002 · **Posted:** Thu Dec 23, 2010 12:05 am

Serge A. Storms wrote:

My 2011 (4200 miles) does it too, seems to quiet a bit after a half minute or so but still makes some noise. One of the Tech Advisors for MOPAR tells me its normal injector noise. I am currently on assignment at a dealer, maybe I will start a couple on their lot to see what they sound like.

BTW, Cool forum, I have read a bunch of useful info. Glad I found it!

Yep and all due to the plastic intake manifold that amplifies the noise.My KJ's 3.7 has done it since mile 3 whne I bought it 9 years ago.

3.7L Knocking when cold

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