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Old 08-26-2014, 08:15 PM   #1
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Engine knock on startup

2011 Automatic Sport DD 51000 miles

I have noticed for a while that on cold starts my 3.8 makes a quick slapping sound for about 2 seconds. Sounds like a dry engine though oil is fine. I use full Synthetic religiously every 5000. I use whatever is on sale at Advance Auto. I typically upgrade to the K&N filter. Current oil is Kentrol. Today when starting for first time in 24 hours the engine made a loud single thump along with the slapping noise.

My searches reveal that this is considered normal. Noise like this tells me that metal is touching metal. How can this be normal? Has anyone else out there experienced this and now are dealing with engine problems as it ages? should I be concerned?

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Old 08-26-2014, 09:14 PM   #2
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It could be the anti drain back valve in your filter is bad. It happens. Try a new oil filter, and pre-fill it as much as possible before installing it. Some engines make start up noise from time to time.

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Old 08-26-2014, 09:17 PM   #3
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Prob not the same thing but my 2012 does this on occasion. Rare and no rhyme or reason to it as far as I can tell.

Edit: just the quick rattle. Haven't had it thump yet.
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Old 08-26-2014, 09:26 PM   #4
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Originally Posted by demarpaint View Post
It could be the anti drain back valve in your filter is bad. It happens. Try a new oil filter, and pre-fill it as much as possible before installing it. Some engines make start up noise from time to time.
I have to admit I've never filled the filter with oil when changing the oil. Just read about that recently. Although I dont get it - I assumed it would fill once I started the motor. What is the mechanical advantage to pre filling?
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Old 08-26-2014, 09:36 PM   #5
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I have to admit I've never filled the filter with oil when changing the oil. Just read about that recently. Although I dont get it - I assumed it would fill once I started the motor. What is the mechanical advantage to pre filling?
You're correct the filter will fill itself. However pre-filling helps to get the oil flowing faster to the engine internals, reducing start-up wear after an oil change. People like myself that are a little OCD prefer to fill the filters, IMO it helps. Some filters hold close to a qt of oil, and pre-filling helps quite a bit, if the filter is situated in a position that allows for pre-filling it.

A bad Anti Drain Back Valve can cause dry starts each time the engine is shut down and left for a few hours. A bad ADBV will allow the oil to drain back into the engine, and you'll sometimes hear start up noise, because the filter has very little oil in it.

The 2012 is a totally different animal, has the filter on the top of the engine and no ADBV.
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Old 08-26-2014, 11:44 PM   #6
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Quote:
Originally Posted by demarpaint View Post
You're correct the filter will fill itself. However pre-filling helps to get the oil flowing faster to the engine internals, reducing start-up wear after an oil change. People like myself that are a little OCD prefer to fill the filters, IMO it helps. Some filters hold close to a qt of oil, and pre-filling helps quite a bit, if the filter is situated in a position that allows for pre-filling it.

A bad Anti Drain Back Valve can cause dry starts each time the engine is shut down and left for a few hours. A bad ADBV will allow the oil to drain back into the engine, and you'll sometimes hear start up noise, because the filter has very little oil in it.

The 2012 is a totally different animal, has the filter on the top of the engine and no ADBV.
^^^This
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Old 03-24-2015, 07:54 PM   #7
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My 2011 4dr Sport Wrangler has been doing this and it started one very cold day in Eastern Oregon. I had no idea what it might be until reading this thread, thanks guys.
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Old 03-24-2015, 10:33 PM   #8
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Normal. My 11 has always done it for 65 k now. Always had a OEM oil filter with replacements, so chances of every one having a defective ADBV? Zero.

Pre-filing the oil filter at oil change time is going to take some luck since it screws on sideways to the engine. Even then that doesn't make a difference on the next start up, or the next, etc.
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Old 03-25-2015, 05:37 AM   #9
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Mine has always done it. The engine will ping under heavier acceleration until warm.
Techron does help some.
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Old 03-25-2015, 06:06 AM   #10
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I don't think the op is talking about valve tap on start up or pinging under load, what he describes is classic lower end issues as in hammering, but as old dogger pointed out this is all speculation and should get it to a reputable mech.

BTW OP, just to speculate a little further. They call it hammering for a reason, it really does sound as though someone is hitting the lower end of the engine block with a hammer, does this describe what you are hearing or is it more of a lighter tapping sound.
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Old 03-25-2015, 06:21 AM   #11
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I don't think the op is talking about valve tap on start up or pinging under load, what he describes is classic lower end issues as in hammering, but as old dogger pointed out this is all speculation and should get it to a reputable mech.

BTW OP, just to speculate a little further. They call it hammering for a reason, it really does sound as though someone is hitting the lower end of the engine block with a hammer, does this describe what you are hearing or is it more of a lighter tapping sound.
I would describe as the sound of a playing card in your bike spokes. Its that fast of a sound. It is only upon startup. It instantly fades to complete quiet within a second. I have no ping or tapping when driving. I'm at 61k miles and no issues to speak of.

After originally posting I realized that my oil was on the low end of safe. I changed the oil and put it to the high end of safe and noticed a decrease in the startup taps. However, it's still there just a little. For all I know this could be the normal sound at startup on the 3.8.
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Old 03-25-2015, 06:33 AM   #12
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my mistake OP, I thought I was responding to a totally different thread about engine noise that was started last night. Please disregard my post above as it has no relevance to your issue, sorry for the confusion.
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Old 03-26-2015, 04:37 PM   #13
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The problem is the oil filters you're using for your 3.8. K&N are actually not good filters to use for dry starts. Over the years there have been a lot of complaints with 3.8 owners using that filter. Use only a Mopar filter or premium Wix. You're actually better off just using the Mopar filters. Some 3.8's I guess will do it on occasion because some in this thread have reported it. Mine has only done it once and I have a 10. Again, there will be a handful of 3.8's that still might do it but I don't agree that it's normal because the majority of 3.8 engines, when a Mopar filter is used, don't give the symptoms of a dry start. Since the filter is horizontal I don't think there will be a benefit to pre-filling. You might get some in there but the position works against you. I know you think you were using a good filter, but K&N filters have had issues with 3.8 JK dry starts. It does have to do with the drain back valve or the lack of one regarding the K&N and many others. Extreme cold weather can cause this at times, even with a Mopar filter.
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Old 03-26-2015, 05:19 PM   #14
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You are not hearing a rod knock.
Probably just lifters and that has nothing to do with filters, except how long it goes on after startup. The lifters sit with valve spring force on some of them whenever the engine is stopped. This allows them to leak down a bit and increase the valve lash from zero to a higher clearance. They take a couple seconds to pump back up with the engine turning and oil pressure. If the filter has drained back it will take a second or two to establish oil pressure at the lifter.

Filling your oil filter is a waste of time on a warm engine that has just been stopped to change the filter. It's not "dry". And it's not oil pressure that keeps the bearings from touching metal to metal. If it was important to do so we'd see failures of engines that have sideways filters, or the manufacturers would recommend filling the filters. But if it makes you happy, do it.

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