01-07-09, 06:15 PM
I have new 98 SLS with 95,000 miles, seems to have been well kept. Its stored in my garage for the winter, but like to start it up every couple of weeks. I dont know if its necessary, but It gives me peace of mind. I start it and let it run for 10 or 15 min, then give it a little throttle now and then.
But last week, AFTER it was warmed up, I started hearing a distinct knocking under the rear valve cover. At idol its a slow knock, about the frequency of a valve opening and closing. I turned off and restarted the engine, and it was quiet till I gave it a little throttle, then came back. I'm talking probably 30-40% throttle, nothing crazy. At first I thought piston slap from carbon build-up, but they say thats only when its cold. Thanks ahead of time, any thoughts would be appreciated!
Do not start it unless you are going to take it out and drive it and get everything (engine, trans and exhaust) good and hot. You're doing more harm than good.
Not sure what to tell you about the noise. Could be lots of things.
01-07-09, 11:32 PM
Get it checked out. I just picked up a Northstar with a worn out lifter/cam on the front bank (left bank). All of that's replaced now and the rest of the engine is in great condition but the longer the engine is run with that noise, the more chance there is for something to go seriously wrong. Hopefully it's something easy/cheap to fix. But get it checked out. I would make sure it has good oil in it before anything else, give it a fresh change with top-quality oil. Thin/cheap oil can cause lifter knock. Also get the oil pressure verified. If you suspect a drop in oil pressure, don't rely on that idiot light in the guage cluster.
Jake is right - it could be a bad lobe - somewhat common on the left bank exhaust lobes, but I think that sound you hear can be pretty normal for 95Kmiles - depends on how loud. My '97 with 148K does that sometimes until all warmed up and full oil pressure has reached the lifters. I think my 2000 with 78K miles is noisier before it's warmed up, also.
01-08-09, 06:27 PM
Yeah, I thought about that, understanding that any engine may make a little valve noise before it warms up. But this didnt start till the engine had idled for 10 or 12 minutes. And it sounded like only one area, rather than a little valve chatter across the board.
But, at some point I will pull the valve cover off and check the lobes. Thanks for the input!
01-10-09, 10:12 AM
Did it sound like this?
3.7M .wav file of my 99 STS with a bad rear exhaust cam at 101K miles.
01-10-09, 11:21 PM
That is exactly it! Thanks! Hmmm, bad exhaust cam... did you replace the cam shaft?
01-11-09, 06:11 AM
The long version is here: http://www.cadillacforums.com/forums/cadillac-seville-cadillac-eldorado-forum/131216-99-sts-n-lifter-noise-advice.html
The short version:
I ended up getting both exhaust cams replaced. :bigroll: Turned out the front was going bad too but the noise from the rear was drowning it out. Motor must come out just to remove the cam covers, much less the cam shafts. :rant2: While it was out they checked the torque on the headbolts, at least 3 spun. :eek: Time for HGs :bighead: and Timeserts while the motor is out anyway. OBTW the lower case half is leaking, :nono: yeah do that too. 46 days and $3967.09 :hide: later I had it back. Even though I'm completely 3x upside down in this car I still :bouncy: it. One problem was finding the cams - they can be difficult to get but I don't remember why. SLS might be easier because they are different cams. By some coincidence the machine shop that checked my heads had a used pair for STS with the original lifters that they let go for $100 :thumbsup: Dealership may not be your friend here, the one I went to told me it would be cheaper just to do a long block replacement than tear the motor down. Of course they also told me the tapping was the wrong weight oil :want: and scooted me out the door with an oil change. If you have a dealer with a good SA that will work with you that might be a choice, otherwise you're lookng for an indy that will work on N* - try calling machine shops and see if there's a mechanic that sends them a lot of N* heads/parts. That's how I found my guy. Let us know your results.