: northstar engine knock help!



ryancaddy99
03-10-08, 01:45 PM
Hi everyone. My 99 Deville, 82000 miles has a light, deep sounding engine knock when idleing. Cant hear it that much in the car but from the outside you can. It does has that piston slap metalic sound when cold. I have done some WOT and out some chevron injector cleaner in. Performance is fine. I have an after marker warrenty on this car which Is good. Any ideas of what this could be? I was going to get some Sea Foam and try to decarbon the engine. I just bought the car a month ago, not even! Other than that, I love this car! Thank you all for the advice and help.

Submariner409
03-10-08, 03:53 PM
Don't go overboard on the TECHRON: it isn't necessary. Has the "tone" of the noise changed, does it die off during warmup, and has the general engine performance changed noticeably since you started with the WOT and TECHRON?

What was the past history of the car? Look at the driver's door sticker, find the build date and calculate miles per month since build. Is it a highway or town car? Looks like around 9 - 10k miles a year, under the national average, so it wasn't a commuter. Go to a Cad dealer and have them pull the car's history (it's a VIN computer entry, GM only) to find all the warranty and recall work.

I'll reserve comment on Seafoam, maybe someone else with hands-on experience, or a GM tech, will chime in.

Ranger
03-10-08, 05:13 PM
Personally, I'd say forget the snake oil. If WOT didn't clean it out, I doubt Seafoam will accomplish anything more.

Could be as simple as a bad idler pulley bearing.

Lithorian
03-11-08, 12:32 AM
ive heard bad water pumps make horrible noises, but lets ask this, is it over heating? or has it over heated at all recently?

ryancaddy99
03-11-08, 12:34 AM
Thank you for responding. I have only put in 1 treatment of techtron. I do recall hearing the noise before put in the treatment. I checked the oil, its full and not due for another 1000 miles. Has not consumed any either. In doing some research, GM has TSB saying these cars buildup carbon and to use GM Top Engine cleaner. It has plenty of B@!!s on WOT. I did notice some grayish color exhaust when flooring it. :lildevil:
As for the history, the car did have its oil change every 3000 miles according to the mechanic that I found who serviced the car.(found recipts in car) It belonged to an older couple. Valve cover gaskets were replaced at 79,000 miles. I use sunco ulta preium fuel. I am avg. about 21 MPG.

What kind of oil and filter should I use? When had it change, they used 10w30 high mileage penzoil. Thanks again for the help!!:bonkers:

Ranger
03-11-08, 11:38 AM
Any 10W30 oil will do just fine. I'd stick with an A/C Delco filter.

dwight.j.carter
03-11-08, 12:17 PM
that could be bad that you bought it from an old couple. That means it probably didn't get it's share of WOT so I would think it has carbon buildup.

tateos
03-11-08, 12:53 PM
The grayish color exhaust is carbon/combustion deposits. Keep doing the WOTs until the exhaust is not smoky - the carbon knock may go away. BTW, I don't think the knock actually does any harm.

bill57
03-12-08, 12:37 AM
How is your oil consumption? There was a bulletin for engine cold knock condition for the 2000 Northstar. Needed to replace my pistons!

Submariner409
03-12-08, 10:07 AM
bill 57,........According to the OP, his oil consumption is minimal. Please post the referenced TSB from GM as this is a brand new idea we've never seen before. Your findings may just render obsolete 12 years of Northstar experience.

ryancaddy99,.....Your car is actually pretty "young", mileage-wise, so there's no real reason to use high mileage oils, but then again, it won't hurt. I and my marine engine business have had very good experience with Shell/Pennzoil (SOPUS) products. 3,000 miles is way too frequent for Northstar oil changes. Even with low mileage use, 7,500 miles a year or even less, you can easily go 5,000 with no problems, oil monitor indication if it's a highway car (If you get antsy, change it at 25%).

porkfarm
03-12-08, 01:19 PM
I had the same problem and did the same steps as you. I used AutoRx in the oil and it seems to have helped. I think it is cleaning out the rings. I put a post in the 2005 STS section and on Bob is the oil guy . com under oil adds.

foos
03-12-08, 07:59 PM
Mine always makes a knock noise when cold and you can hear it somewhat at idle when it's warm.. I think it has always done it.. I doubt there is any problem.. I WOT a lot.. I even WOT and maxed out RPM in 3rd gear several times and it still does it.. Who knows :P
I wish it made absoutely no noise from the rotating assembly but oh well.. maybe after I rebuild someday.. It has 108k miles on it and runs just fine, although burns a lot of oil, probably because the pedal is on the floor more often than not.

porkfarm
03-12-08, 09:39 PM
You should check out all the talk about autorx and stopping oil consumption. Like I said, In the other post. I like my car now ! I hated the sound of the valve train so much, I was getting ready to trade it.

bill57
03-13-08, 09:21 PM
sub...409,
I'm not sure of the update Northstar Bulletin number. How many characters long might it be?
In my case, my 2000 Deville was consuming more than 1 qt. oil in 2000 miles, and there was a knock after initial starting. The dealer confirmed the oil usage, and during diagnosis, found the pistons to be excessively noisy, and replaced them all "per update Nothstar Bulletin for Engine Cold Knock Condition".

aarcuda
03-13-08, 09:59 PM
Personally, I'd say forget the snake oil. If WOT didn't clean it out, I doubt Seafoam will accomplish anything more.

Could be as simple as a bad idler pulley bearing.
without reading all the comments here, this one I agree with. Snake oil never cured a real engine problem

Tonkin
05-27-08, 06:36 PM
How is your oil consumption? There was a bulletin for engine cold knock condition for the 2000 Northstar. Needed to replace my pistons!

Yup !! Just happened to me. Thought I had lifter noise but when I took my 2002 DHS in for the problem today they said it was piston noise. Oil consumption is 1 qt / 3000 miles at oil change, I do WOT once a month or so with no black smoke, and the dealer just told me they are replacing all pistons for "the cold knock problem" per a service bulletin.
The car has 57,000 miles. Good news is car has warranty till sept 2008! love that warranty.

He said they replace them from the bottom. Is that correct?

Ranger
05-27-08, 06:59 PM
Now you got me worried Tonkin.

AJxtcman
05-27-08, 07:05 PM
Yup !! Just happened to me. Thought I had lifter noise but when I took my 2002 DHS in for the problem today they said it was piston noise. Oil consumption is 1 qt / 3000 miles at oil change, I do WOT once a month or so with no black smoke, and the dealer just told me they are replacing all pistons for "the cold knock problem" per a service bulletin.
The car has 57,000 miles. Good news is car has warranty till sept 2008! love that warranty.

He said they replace them from the bottom. Is that correct?

Tonkin and Portland that is funny. :eek:

I have done a lot of the pistons.
so do you have an in at a dealer?

Tonkin
05-27-08, 07:11 PM
Ranger, your warranty should be good a year longer then mine! :thumbsup: Bought this in Jan 2006 with 48000 miles and it had noise then. But I thought it was normal. I commented at the time how much quieter my 1996 concours was. It got louder in the last few months. Sure sounded like lifter to me though. Parts will be in Monday they said. :rolleyes:

Tonkin
05-27-08, 07:15 PM
Tonkin and Portland that is funny. :eek:

I have done a lot of the pistons.
so do you have an in at a dealer?

No "IN" .. just a warranty. :)

Tonkin is ref to "Gulf of Tonkin" 1964 NOT the car dealer :eek:

Ranger
05-27-08, 07:32 PM
Ranger, your warranty should be good a year longer then mine! :thumbsup: Bought this in Jan 2006 with 48000 miles and it had noise then. But I thought it was normal. I commented at the time how much quieter my 1996 concours was. It got louder in the last few months. Sure sounded like lifter to me though. Parts will be in Monday they said. :rolleyes:
Yeah, I'm still covered until next year sometime. The good news is that she is quiet as a mouse.