Greetings JKU,

Not sure I am over thinking this but lately I've noticed that when I go out to start the JK the engine rattles for a few seconds then stops. Not a 100% where its coming from but it sound internal engine? If I were to put a description to it it resembles what a dry start up would sound like. I do not recall it doing this when I first bought it but perhaps it did and I am just paying more attention to it now that I've had it a few months.

2017 JKU with stock engine. Oil is fresh and full. Is this a common thing or something I should worry about? I remember having a late 80's 2.9L that did this and never had any real issue other than it sounds terrible. I've done some googling and it appears to be a think on the 3.6 penastar. I'll continue researching but thought I'd ask the pro's.

Thanks in advance,

Cheers

Nem

 

I think it's because we have hydraulic valve lifters in the 3.6.

"Frequently, the valvetrain will rattle loudly on startup due to oil draining from the lifters when the vehicle is parked. This is not considered a significant issue provided the noise disappears within a couple of minutes; typically it usually lasts only a second or two."
https://en.wikipedia.org/wiki/Hydraulic_tappet

There's a good bit of discussion out there on this.
Mine goes away pretty quickly but it's there.
I think to myself 'engine wear +1' every time I hear it.

 

Just the gaps filling in because the oil drained out from when it was last shut off. Just ensure you give it some time when cold starting to warm up and circulate the oil a bit before moving. Something like 30-45 seconds is enough then drive lower power for first couple of miles. My parents in New Zealand bought a Nissan 2.0 car in 1999 when it was a year old and it rattled on every cold start at 20,000kms. Fast forward to last Feb 2020 I was down there again and at 158,000kms the same rattle still there and car runs perfect.

 

Thanks you guys! After I posted this I was able to change a few words and learned pretty much the same as you're telling me now. I am with you go4lo, any type of engine rattle makes me cringe. Otherwise the 3.6 runs well. It only has 33k on it.

Would going to a 5-30 have any improvement? Here in this part of Cali it can get to 110 pretty fast. Although in the winter months its has been as cold as 25.

Cheers and thanks guys

 

I've had a similiar behaviour with my 2007 JK Rubicon. I wasn´t really worried at the begining, but lately I am noticing that the brakes are also diminished for the first couple minutes. After a couple blocks (and very careful driving) the sympthom is gone. I believe this might has to do with the hydraulic fluid, but I'm not sure, as I am not an expert.
Also, I got recently a P0522 code, not sure it's related.
Any advice?

 

My 2 cents here. I had a similar issue on our 2016 JKU. It isn’t driven a lot, so when it started, I could hear a slight rattle. It was just for a second or two, but it drove me nuts! After doing some research I discovered that the oil would drain out of the OEM cartridge filter, so for a second or two you’re “dry”. I solved the problem by replacing the cartridge style filter with a Baxter Performance spin-on oil filter adapter. Noticed an immediate difference on startup! Now, the oil stays up top and when you start the engine, the oil is there. Like I said……my 2 cents, but I have never regretted the swap!
Good luck!

 

Same kind of problem Agent 915 except mine is with a 3.8 with the filter laying in the bottom front of the engine. I read the same type of stories about the filter, one person said use Wix, a couple more said use Mopar from the dealer. I still have the startup noise and I was told by 2 people it is probably the timing chain needs adjusted or replaced...IDK

 

I'd give every thing a good visual and shake looking for something loose. Check the exhaust starting at the engine and look for heat shields that have broken welds. How's the coolant level. Does the level in the reservoir vary from cool to hot. If you have air in the engine,coolant, it makes that sound when cold starting. Try burping the radiator.