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Unread 03-04-2013, 05:00 PM   #1
godfather901
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2008 3.8L problems

2008 3.8L 20,000 miles consumes a lot of oil, after reading the numerous threads I wouldn't care that much since I could just add oil more often - but there's another issue. There is a knocking noise that's slowly getting worse - it only happens under heavier than normal load (i.e. uphill, highway on-ramp acceleration) and it's not rpm based, sounds like knocking (single rock in a coffee can) not lifter tick. I've switched to 5W-30, but there was no change in the knocking frequency or volume. I'm a decent mechanic, but I'm not sure how to diagnose a random noise I can't pinpoint. Any help you guys have would be appreciated.

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Unread 03-04-2013, 05:11 PM   #2
ncb
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Is it knocking or is it pre-ignition pinging? My 2009 pings on warmer days and after researching the issue online I'm planing to use the combustion carbon cleaner that Mopar sells. I've seen a couple reports that the cleaner clears it up.
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Unread 03-04-2013, 05:56 PM   #3
godfather901
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I'll check that out, not sure if it's pre-ignition or not but if an additive can clear it up that'd be awesome.
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Unread 03-04-2013, 07:23 PM   #4
ncb
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It's an aerosol that you spray in the intake while its running. Makes a good smoke screen from the video I watched.
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Unread 03-04-2013, 09:52 PM   #5
JTPhoto
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It could be a cracked exhaust manifold..
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Unread 03-04-2013, 10:00 PM   #6
SkipperTW
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Are you the original owner? My 09 was under (what I thought was the last year of a couple) that they offered the Lifetime PowerTrain War to original owners... Might be worth looking into. If you keep the oil up and it eventually blows, you can get a new engine (or anything PowerTrain related for around a $100.00 deductable. Just make sure you get the regular checkup scheduled in the manual and you may be golden... Just a thought.
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Unread 03-05-2013, 12:42 AM   #7
godfather901
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I am not the original owner, I bought it used with 300 miles on it (who trades in a jeep with 300 miles?) and I change my own oil... which seemed like a perfectly fine idea until now. I don't think it's the exhaust manifold as I would assume it would tick all the time if there was a leak. I'll still pop the heat shield off and take a look though, thanks for the tips.
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Unread 03-05-2013, 06:21 AM   #8
LIJeepJC
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Quote:
Originally Posted by godfather901
2008 3.8L 20,000 miles consumes a lot of oil, after reading the numerous threads I wouldn't care that much since I could just add oil more often - but there's another issue. There is a knocking noise that's slowly getting worse - it only happens under heavier than normal load (i.e. uphill, highway on-ramp acceleration) and it's not rpm based, sounds like knocking (single rock in a coffee can) not lifter tick. I've switched to 5W-30, but there was no change in the knocking frequency or volume. I'm a decent mechanic, but I'm not sure how to diagnose a random noise I can't pinpoint. Any help you guys have would be appreciated.
To me the knock under load is due to dirty combustion chambers or bad gas, or could be a bad o2 sensor.. Etc. one other question for you... You mentioned you burn thru a lot of oil... Have you ever let it run down too low? Maybe when the low oil light came on (is there one?)? I ask because the knock could be main bearings. I can't tell cuz I can't see your truck so I am just throwing that out there... Good luck
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Unread 03-05-2013, 04:23 PM   #9
godfather901
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Quote:
Originally Posted by LIJeepJC View Post
To me the knock under load is due to dirty combustion chambers or bad gas, or could be a bad o2 sensor.. Etc. one other question for you... You mentioned you burn thru a lot of oil... Have you ever let it run down too low? Maybe when the low oil light came on (is there one?)? I ask because the knock could be main bearings. I can't tell cuz I can't see your truck so I am just throwing that out there... Good luck
This was also my assumption. I dumped some injector cleaner in the tank today, just to see if there was any change over the next 15 gallons or so. It's not the gas unless multiple stations across the country all have bad gas. The oil did get very low once, no idiot lights, and it still showed up on the dipstick - but before I knew I had an oil consumption problem, I drove for about 2000 miles without checking the oil and it was about 2 - 2 1/2 quarts low. I got a little time under the hood today at lunch, it is possible there is an exhaust leak and the knock is more from the resonance of the heat shield... I won't know until I can get my tools, and they're not coming in for a week or so. Again thanks for the help guys, if nothing else it at least gives me some things to check out while I'm limited on work areas and tools.

Slightly off topic, but it's not outside my capabilities to rebuild the 3.8... can you check the main bearings just by popping off the oil pan on these engines while they're still mounted?
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Unread 03-06-2013, 08:52 AM   #10
Monstrousmac
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It could very well be a Hydraulic Lifter. What you can do is change your oil and add 5 qts of oil to one quart of Transmission fluid. Transmission fluid has cleaners in it. Run it at idel for about thirty to forty minutes and then do another oil change and see if that helps. I have also seen a bent push rod create a knocking noise that is random. They are simple to swap and rather inexpensive.

Here is a link similar to what I told you http://forum.miata.net/vb/showthread.php?t=193131
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