5.7L Hemi Ram 1500 rod knock when cold

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Dec 16, 2012
Oklahoma, USA
Hi Everyone,
I own a 2012 Ram 1500 with a Hemi. Now that it's cooler early in the mornings, my truck has what sounds like a rod knock on a cold start. It persists until it warms up. The truck only has approx. 30k miles on it and is still under warranty. I took it to the dealer last winter and, of course, they said they didn't notice anything wrong or hear any noises (they even said they checked the exhaust manifold bolts to make sure they weren't broken). I don't get it, the noise is very obnoxious, and consistent when it's cold outside.
I change the oil every 4k miles myself with synthetic 5w-20 of various brands. Any ideas? Thanks for your time
Rod knock gets louder as the oil thins so it is very doubtful it is rod knock. It sounds like, as Chris stated, piston slap.
I appreciate you taking the time to answer a question that has probably been beat to death, it just has me worried. If it is piston slap, does that mean that the piston skirts have already been worn down? Maybe I should contact Chrysler and try to replace them under warranty. I only buy chysler products, surely they would try to rectify the situation?
You can ask them about it. There were GM engines that slapped like crazy and still lasted and lasted so I wouldn't be overly concerned about it. I think it is an embarrassing sound more than anything.
It could be the infamous "Hemi Tick" that a ton of the 5.7 Hemis have. It could also be the previously mentioned piston slap that the 3.1 and 5.3 GM engines are notorious for.
I would take it back to the dealer. Call corporate about it if they don't do anything. It might be piston slap, but it also might not be. If its not you need to have the issue fixed while under warranty, thats what a warranty is for. If it does end up being piston slap, there isn't much to worry about. My Honda K24 has piston slap year round on every "cold" start, even in the summer.
I have the same engine & same year Hemi. What type of oil filter are you using? I use a Mopar Filter and it's quite quiet upon startup . My truck sometimes sits for weeks on end too!
every piston and every cylinder is slightly different.say the clearance is supposed to be .0025-.0004.a slightly small piston and a slightly larger bore may have .0005-.0007 clearance. wont hurt anything and when things warm up the clearance lessens and the noise goes away.

add in todays short piston skirts and we have many more complaints than we had 20 yrs ago.
There are many Hemi's with the wrong size size pistons causing these problems. Don't let up on them. Yes there is a Hemi "tick", not the same as piston slap. Some almost sound like a diesel as its warming up.
I too have that same model year and engine. I haven't had this issue so far. Bought it used in 8/2013.

Came with some quick oil change place 5W-20 syn blend (Castrol window sticker - means nothing) & who knows (shop) filter. OCI alert came on Jan. 2014, no way I was changing it myself in that weather. Got fresh National (Pinnacle) syn blend & shop filter from AAA Car Care Plus. OCI alert came on again in June 2014, did change myself with National (Pinnacle) conventional & PureOne filter. Learned OCI alert maxes out at 3500 miles in this model. Changed last week to PPwPPT and a M1 filter, this will set my REAL OCI in April & Oct or 8k miles going forward.
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Don't know about the Hemi, but my 4.7 Dakota makes a lot of noise on cold startup-but pretty quiet when warm. Some research led me to an article about how later 4.7s has different lash adjusters that took care of the noise issue.
My old 04 hemi made some noise when cold in the bottom end too. My brothers 08 knocks til warm as well.
I really noticed the knock until I used defy 5w-20 and on the next cold start the knock was barely perceptible.
Is it consuming any oil or any other problems that your aware of?
I have owned many autos, never had that piston slap thing. Never heard anyone in the 50s, 60s, 70s,80s discuss that thru my life travels--- the new generation of drivers have watched played to many of those video games and are now hearing noises that aren't there. If I want to eliminate noise, I just take out the hearing aides and life is good- lot of truth to that.
Someday you might be there.................
I have had 2 hemis, a 5.7 and now a 6.4, and neither had piston slap. I do have a 1999 GMC Sierra with a 5.3, the ones notorious for piston slap, and it does have very noticeable piston slap in cold weather when first started up, particularly after sitting for a few days. I am not worried about it since it is a well known problem and I have never read any reports of an engine failing because of it, even after all of these years.

My understanding of the cause in the GM engines is the use pistons with a short skirt. The hemi uses a similar design, but is not known for having this problem.

I would persist with trying to get Chrysler Corp. to document your problem. You may have to go over the dealer's head and contact Chrysler directly.
It could also be carbon knock. Cadillac N* had this problem and it sounded like rod knock. It went away once the engine was warm.
Don't mess with it take it to the dealer,leave it overnight if necessary.
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As above, it's likely to be piston slap due to the described symptoms.

A local Ford dealer (a big one) was switching 5W-20 for 10W-40 synthetic. Piston slap issues are resolved by this. As are cam phaser knock issues.

In my case, my 5.4L F150 (70K miles) has awful cam phaser knock with the recommended 5W-20 oil. I moved to M1, 10W-30 and the issues is nearly "gone". And, my UOA results show half the wear metals per 1000 miles.

I can't suggest a repair course of action, as I'm not at all sure the dealer will give you a better engine, if you are successful in convincing them to replace or rebuild it.

But, in your location, I'd give Mobil 1, 5W-40 a try. It's a very robust synthetic, will flow well when very cold, yet remain viscous enough to reduce piston slap.

Many, many, many modern engines with short skirt pistons exhibit piston slap when cold. This generally does not reduce engine life at all.
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