Rattle on cold start

Hi There, First post.

I am the new owner of a 2002 Renegade in Dog Vomit green. Bought her at 13750 miles. I've put about 75 on her now and I'm noticing in the morning on a cold start she lets out a soft rattle. It's only there for about 30 seconds and then it's quiet for the rest of the day. No hesitations, shifts smooth as butter, no heat issues. I did see a post from ShafferNY from 2009 that seems to exactly describe the noise. (FYI, Mods I'm making a new one to avoid Necroposting) under "Rattle at startup".

I was just curious if anything new had been found about the source of the noise and, well, if i should be scared of her exploding, dying or catching on fire since she's less than 7 days off the lot. People seemed to go both ways in the other post so I was unsure. Now is when I could go back to the dealer and say rude things until they helped me, so now is the time to do it.

I'm tempted to bring her to a Jeep dealer in my state (NH) for a once over, but that leaves me without a car for X days and they'd have to have her at least overnight to replicate the wonderful morning song of her people. Not to mention I'm in the middle of nowhere and the only dealers near me are an hour plus away.

Beyond that, I have to say I'm absolutely in love with her. I'm going to happily invest a few thousand in aftermarket toys...once I'm sure(ish) I won't have to sink it into an engine or ****** any time soon first.

Wouldn't worry about it, these engines are a little knocky on cold starts. Maybe send the oil for an analysis.

HoosierJeeper said:

Wouldn't worry about it, these engines are a little knocky on cold starts. Maybe send the oil for an analysis.

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where would i send it? I'm new to the area and am going from a Caddie to a Jeep so I haven't picked a new mechanic yet.

Blackstone labs I think is the place, or at least the most common one.

My 12kk has a cold start rattle. I just thought it is normal. Now my 06kj only rattles when it sits for a week or more.

Have you guys tried running some seafoam through the brake booster vacuum hose? It will clean up some of the carbon deposits and could fix the noise. There's a thread on here somewhere that describes the process to seafoam.

I had a rattle that seemed more prominent when cold and it turned out to be the heat shield on the driver side catalytic converter. Put a hose clamp around her and never rattled again.

Definitely check the vehicle for rattles on exhaust ^ as mentioned.
Mine sounds like this in the AM, click on image to hear/see video:
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Use a good quality filter & synthetic oil and I found that Bio-Tech really quiets her down.
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I have a slight piston slap at cold start. The problem is the knock sensor picks it up as an ignition knock and tries to correct it and makes it worse. Turn the key off then start it up the knock is gone till the knock sensor kicks in. Then it's back.

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CalcityRenegade said:

I had a rattle that seemed more prominent when cold and it turned out to be the heat shield on the driver side catalytic converter. Put a hose clamp around her and never rattled again.

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Had the same thing on the 04, now the 03 has it every now and again

Do you have a video of this? I've dealt with every rattle/tick/clunk this 3.7 has. Sounds like timing chain rattle by the way you're describing it. The tensioners are bleeding oil out when it's sitting causing it to rattle until pressure is achieved


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