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Thread: Engine has knock when cold
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07-05-2007, 05:26 PM #1
- Join Date
- Jun 2007
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- Baltimore, MD.
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- 728
Bright Red- 2000 Pontiac Trans Am WS6
Engine has knock when cold
I just picked up this 2000 SS Camaro a week and a half ago.
When engine is cold, it has a noticeable "knock" that sounds like a rod knock. It is definitely NOT a valve tap...it sounds much deeper.
When engine is warmed up, the noise is all but non-existent.
Oil pressure reads 60psi at light throttle cruise
Just shy of 40psi at warm idle
50psi at cold idle.
Original owner said he used Mobil1 only.
Engine has 110,000 miles but runs fantastic.
If you rev the engine up, noise is gone...or at least I cannot hear it then.
I tried SEARCH function here and elsewhere and most engine knocks seem to be when HOT, not when COLD....
Any ideas?2002 Silverado Z71 ECSB HPTuners tuned by yours truly
2000 Pontiac Trans Am WS6 6.0, 4L80E, 9" rear
webpage: http://www.fquick.com/rel3rd/
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07-06-2007, 01:14 AM #2
Probably the pistons banging around until the warm up and expand. This is commonly called "piston slap". The good news is that your goes away upon warm-up. Keep a close eye on oil consumption...
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07-06-2007, 06:40 AM #3
- Join Date
- Mar 2007
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- Minnesota
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83 Z28 new project- 98 Formula WS7-sold:(
I have a 98 and it does the same thing. It gets really noticeable when its 5 below zero.
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07-06-2007, 05:09 PM #4
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07-06-2007, 07:37 PM #5
Mine has the slappy slappy too untill she gets warm. It eats no oil. Just start it and go back inside the house for 5 minutes LOL thats what I do.
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07-06-2007, 07:38 PM #6
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07-07-2007, 09:01 AM #7
You could try using different brands/weights of oil and see if any reduce the slap, but I doubt it. Short-skirt pistons, long-ish rods and low tension rings are the culprits...
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07-07-2007, 09:06 AM #8
- Join Date
- Jun 2007
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- Baltimore, MD.
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Bright Red- 2000 Pontiac Trans Am WS6
I plan to try that soon. I drove it to work this morning...loud as heck when I first started it, quiet as a mouse 5 minutes later....weird...
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07-07-2007, 09:10 AM #9
Yah. Once the pistons warm up and expand, there is no room in the bore for them to rock and slap. I had some decent slap in my old 5.0 GT, but it never caused any issues...
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07-07-2007, 09:41 AM #10
- Join Date
- Jun 2007
- Location
- Baltimore, MD.
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Bright Red- 2000 Pontiac Trans Am WS6
I feel much better about it now, thanks to all the feedback and after Google-ing the heck out of "piston slap", lol.
When I first looked at the car, it had just been parked, so it was already warm. I drove it, loved it, and bought it, and the next time I saw it was a few hours later when they delivered it to my house (so they could get their tags off the car).
It was definitely a bit un-nerving when I first started it cold , and of course I thought the worst since I didn't know about the knock problem alot of these LS1's evidently have.
No regrets at all though...
Bought an 89 LX coupe about 2 years ago for $2500
Fixed it up a bit and sold it a year later for $5500
Took that $5500 and bought an 85 Vette.
Sold that a few weeks ago for what amounted to $8000
Then bought my first LS1 car...
I thought my $2500 SS needed an engine...but now that I know different, it's all the better.
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07-09-2007, 05:12 PM #11
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- Jun 2007
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- Hoyt Kansas
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- 17
black- 1969 camaro
Allright guys, heres the deal.. the noise is carbon buildup on the top of the pistons. You can pull the plugs and pour old school carb cleaner in the holes, let it eat for an hour, then turn over the motor( and yes... make a mess), emptying the cylinders. Install the plugs and fire it up. the noise will be taken care of for about 20k miles. oh and change the oil too.
I am shop foreman for a gmc dealer and have run across this many times. the noise will not hurt anything. GM considers it normal, something to due with no skirt pistons and carbon build-up. The only thing I can Gaurantee is that it will return.
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07-09-2007, 06:10 PM #12
you think sea foam will fix it??
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07-09-2007, 08:23 PM #13
- Join Date
- Jun 2007
- Location
- Hoyt Kansas
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black- 1969 camaro
not familiar w/ sea foam, anything that eatscarbon will work, superclean wil eat the carbon but you would have to washit out w/ water and that promotes rust... use the carb cleaner undiluted.
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