: Headgasket/Rod Bearings/Carbon Buildup

04-04-04, 10:56 PM
:suspect: I need your input. I've just had my 1999 Cadillac Deville in for dealer service. It has 66,000 miles. I change my oil and filter every 2500 miles and put STP gas treatment/fuel injector cleaner in my gas tank about every third tank full.

I had been noticing some burning oil in the engine area, not the exhaust, with a minor drip here and there, and wondered if a head gasket was going. I also noticed a "ticking/knocking" noise from the engine at all times. The dealer checked out the noise and told me there was a carbon buildup on the rods so they added a cleaner to help that, then told me that there was a bulletin out about the rod bearings making noise too. After spending a few thousand dollars to replace all the rod bearings, I'm still hearing some noise on the passenger's side of the engine where all the belts are. I've seen an A/C compressor hub bearing bulletin (is this correct?).

I'm wondering if the original problem was just the head gasket that created the carbon buildup. Logical? I've read on one of the posts here that antifreeze in the oil can wear out bearings. Is this true?

Thanks all! :)

04-05-04, 09:53 AM
Carbon does not build up on the rods :confused: , it builds up on the top of the pistons, start doing a few W.O.Ts with the car on the freeway and watch your rear view for black smoke. Keep on throttle till you don't notice anymore smoke. The Northstar is high performace engine and does not like to be driven with a light foot. You can use 87 octane fuel in stead of premium this will help reduce the carbon build up on the top of the pistons. The dealer can perform a decarb if your problem continunes. You may have a valve cover leaking oil and its dripping on one of your exhaust manifolds or an oil leak from your crank seal and its bolwing back on the exhaust. I have seen serpintine belts cause a ticking noise ( but not on an N*) you can verfiy this condition by removing the belt and starting the car, listen to see if the noise if gone. Sometimes a sticking lifter can cause a tick noise. Both the carbon knock or lifter noise useally happen on a cold start then quit down after the engine is warm. I could not find a bulletin for the rod bearings or A/C hub bearing. Removing the serptine belt will also help determine this conditon. Ief the noise is gone after the belt is removed then you have narrowed down your problem. I am willing to bet you baby the car start driving a little more aggerasivley the N* likes it. Keep changing your oil like you have been.
Lets us know what happens take care,

04-05-04, 10:17 AM
Do not use 87 octane fuel! Use premium gas; 93 where possible

04-05-04, 10:33 AM
:worship: Thanks Frank T. Two days after I drove it home from the dealership after replacing the rod bearings, all the transmission fluid leaked out onto the floor in my garage. I put more fluid in it and drove it back to the dealer for fixing. :hmm:

I drive it a balance of highway and city miles everyday as my drive to work is 25 miles one way and half of that is 70MPH on a freeway. What's WOT spelled out? I'm new to this.

I would never have thought that using a premium grade fuel would cause carbon buildup. I had suspected the STP fuel additive that I had been putting in the gas tank every third fillup first, but that's suppose to prevent buildup too.

The carbon deposits Bulletin is 99-06-01-01A, and I believe that was the first fix using the top cleaner to remove the combustion chamber deposits.

Would the serpentine belt issue come up on the diagnostic codes?

04-05-04, 03:36 PM
Wide Open Throttle

04-05-04, 07:41 PM
Why do you say not to use 87 octane :hmm: ? If 87 octane burns faster than 93 it should burn a little cleaner. If there is no spark knock or loss of perfomance what harm could it cause to the engine? I was told by a Cadillac dealer that this was a recommed by GM to help reduce this carbon build up issue, was I mis-informed :confused: ? If so I will return to using 93 in my 99 STS. I have not notice any performance loss when I switched to 87. Also doing the WOT wide open throttles the carbon knock is gone.
Thanks for your input,

04-05-04, 08:32 PM
I'm afraid to try and explain it as all this car jargon is tuff for me, but I will refer you to a post that seems to explain it fairly well:

I'm sure others will jump in here too. It's important to run premium in these big, hi-performance motors, and I've never seen any knowledgeable people on the forum say otherwise.......Tom

Thanks Panther!

04-05-04, 11:04 PM
That post explains it well, I don't hear any spark knock on my N*. But now :hmm: I also recall hearing about inaudible spark knock that can also do some engine damage if it persist for any leghth of time. lgerken, keep using 93 octane.