Jeep Garage  - Jeep Forum

Jeep Garage - Jeep Forum (http://www.jeepgarage.org/forums.php)
-   Engine Performance/Intake/Exhaust (http://www.jeepgarage.org/f183/)
-   -   Knock On Startup (http://www.jeepgarage.org/f183/knock-on-startup-27524.html)

GratefulDeadWK 08-23-2011 02:48 PM

Knock On Startup
 
I noticed sometimes on a cold start I will get a little knock for a second or two. Anyone else have this issue? I have a 3.7 with 106K and It does not burn any oil? Weird....

lll2for3lll 08-23-2011 03:22 PM

Re: Knock On Startup
 
Does it sound like sound like a wrench hitting a pole?

GratefulDeadWK 08-23-2011 03:29 PM

Re: Knock On Startup
 
not really sounds like a little bit of valve train noise

lll2for3lll 08-23-2011 03:36 PM

Re: Knock On Startup
 
Like bad timing?

mrtosh 08-23-2011 03:38 PM

Re: Knock On Startup
 
3.7 and 4.7 do have some piston slap that's prevalent on cold start up. Nothing to be worried about as the noise will subside as the piston expand and warm up.

lll2for3lll 08-23-2011 03:43 PM

Re: Knock On Startup
 
Yeah. I have that noise too. I hear it in a lot of autos on start up. I mostly hear it in Chevy Blazers and Tahoes.

2005JGC 08-24-2011 01:00 AM

Re: Knock On Startup
 
Quote:

Originally Posted by mrtosh (Post 471531)
3.7 and 4.7 do have some piston slap that's prevalent on cold start up. Nothing to be worried about as the noise will subside as the piston expand and warm up.

Yep piston slap can happen, they are 0 tolerance pistons that have a coating on the side of the piston and when that coating wears it can give the piston room to rattle a little till things expand.

Typically some clatter on startup comes from the valvetrain. perfectly normal on hydraulic valvetrain with some miles on it, the lifters can bleed down and have to pump back up after sitting.

Either way, its pretty common and normal. Keep fresh oil in her and so long as one of these is legitamently what it is it will continue plugin along for another 100k.

GratefulDeadWK 08-24-2011 09:16 AM

Re: Knock On Startup
 
Quote:

Originally Posted by 2005JGC (Post 471907)
Yep piston slap can happen, they are 0 tolerance pistons that have a coating on the side of the piston and when that coating wears it can give the piston room to rattle a little till things expand.

Typically some clatter on startup comes from the valvetrain. perfectly normal on hydraulic valvetrain with some miles on it, the lifters can bleed down and have to pump back up after sitting.

Either way, its pretty common and normal. Keep fresh oil in her and so long as one of these is legitamently what it is it will continue plugin along for another 100k.

Yupp, You guys pretty much nailed it. Was gonna reply and say it was like piston slap. It doesn't happen all the time either like y'all said, so I think ill be fine. The 3.7 is a pretty stout motor from what I've experienced. It uses hardly no oil after 3500 miles so that's a good thing for me coming from a Subaru Legacy.

Always keep on top of my oil and change it regularly. Thanks for the help!:)

lll2for3lll 08-24-2011 10:05 AM

Re: Knock On Startup
 
Same here. The oil is clean every time when it's changed. And I don't get the noise all the time.

mrtosh 08-24-2011 11:32 AM

Re: Knock On Startup
 
You should hear a Hemi on startup after sitting over night. Sounds like a sewing machine for about 30 seconds. The liters bleed down pretty quick on the 5.7's. I agree the 3.7/4.7's are pretty stout motors and essentially the same, minus two cylinders. Only thing you want to watch is NEVER let them overheat. Very weak head gaskets.


All times are GMT -5. The time now is 12:40 AM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Copyright 2012 - JeepGarage.Org
The Jeep Grand Cherokee Owners Community