Cold Carbon Knock? Thought I ate another exhuast cam...
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  • 2 Post By Ranger
Cadillac Seville / Cadillac Eldorado Forum Discussion, Cold Carbon Knock? Thought I ate another exhuast cam... in Past Cadillac Vehicle Discussion; So I started the STS up yesterday and hear a tap tap tap tap tap from the motor. Put a ...
  1. #1
    chubbyranger is offline Cadillac Owners Connoisseur
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    Cold Carbon Knock? Thought I ate another exhuast cam...

    So I started the STS up yesterday and hear a tap tap tap tap tap from the motor. Put a stethoscope on the front valve cover and hear an all too familiar tapping around cylinder #4. Flashback to the last time this happened and it ended up being bad exhaust cams that led to headgaskets and a lower case half reseal. Hoping for a sticky valve lifter I changed the oil (OLM @ 25%) with 10W-30 Mobil 1 High Mileage (API CF and non-Energy Conserving that its lived on since the HGs). It was a little low but I drained out at least six quarts. Same old tap tap tap after the oil change. Pulled it out of the garage and noticed two nice fresh carbon spots on the garage floor. Made an appointment with the mechanic but figured I'd drive it anyway; another 35-40 miles later she purrs like a kitty again. I was in the intake recently and noticed its pretty gunky; cleaned the butterfly and what I could reach. I also switched from anybody's high test gas to Shell or other top-tier fuels in the last 1200 or so miles. Since I know bad cams don't go away after they've started is it possible its just flushing some carbon through the cylinders?

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Cold Carbon Knock? Thought I ate another exhuast cam...

    It's magic. Drive the car. Good oil, good maintenance, well-driven car. Ticks come and go. It's mechanical...........

    The two black spots under the mufflers ----- condensation weeps from the muffler drains. normal.

  4. #3
    chubbyranger is offline Cadillac Owners Connoisseur
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    Re: Cold Carbon Knock? Thought I ate another exhuast cam...

    These blacks spots aren't usual for this car though, otherwise there would be more I would notice. Maybe its just paranoia from the last time I heard that sound and it was $3,967.09 and 46 days later before I drove it again

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    Jailtime is offline Cadillac Owners Fanatic
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    Re: Cold Carbon Knock? Thought I ate another exhuast cam...

    Never had cold carbon knock in either my SLS or my STS. Maybe it's that bit of spirited driving on a rural highway every weekend. I hope I never get it, I don't need any more things to worry about on these Caddies.

  6. #5
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Cold Carbon Knock? Thought I ate another exhuast cam...

    Quote Originally Posted by chubbyranger View Post
    These blacks spots aren't usual for this car though, otherwise there would be more I would notice. Maybe its just paranoia from the last time I heard that sound and it was $3,967.09 and 46 days later before I drove it again
    Has your gas mileage gone down lately ??? A bad FPR will cause a rich mixture and therefore black weep spots.

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    97EldoCoupe is offline Owner of Northstar Performance
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    Re: Cold Carbon Knock? Thought I ate another exhuast cam...

    What the older 93-99 Northstars need is an upgrade kit. This upgrade should consist of an oil rail that runs above each of the exhaust cams and squirts oil on the lifters.

    I see perfect intake cams and lifters ALL THE TIME and usually minimal exhaust lobe wear. If the lifters have just a touch of wear, they can go for a long time without issues PROVIDED they get adequate oil of the correct type. Once the lifters stop spinning in the bores, the clock starts ticking on the life of that lifter.

    The only reason the exhaust have a short life-span is the angle of the lifter- the intakes are on less of an angle and therefore oil doesn't run off as quickly

    Keeping up to oil changes and never allowing the engine to overheat are the best ways to save the cams/lifters. Also stick to a good oil - Rotella / Quaker State / Valvoiline / Mobil 1 / etc.

    OLM's are worthless IMO. I have 6,000 kms (3,720 MI) on my truck since my last oil change and the OLM still shows 69%. In my opinion I am about 1,000 kms overdue for an oil change. I let it go this time because #1 - 90% of those miles were turned on in less than a week driving almost steady through the USA at 75 MPH and #2 - I haven't had time to change it. My #2 reason is no excuse though.

    But anyone who believes oil should last 18,000 kms or 11,000 miles, needs to see the internals of an engine more often. This includes the engineers at GM who programmed the OLM data into the PCM.

  8. #7
    Jim 99 eldo's Avatar
    Jim 99 eldo is offline Cadillac Owners Fanatic
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    Re: Cold Carbon Knock? Thought I ate another exhuast cam...

    Jake at what % of the OLM do you suggest performing a drain?

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    JoeTahoe is offline Cadillac Owners Fanatic
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    Re: Cold Carbon Knock? Thought I ate another exhuast cam...

    hey jake do you have that update or could you tell me more about it for a 99 sts and just a reminder how about that e-mail Quote gearheadjoe

  10. #9
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Cold Carbon Knock? Thought I ate another exhuast cam...

    Quote Originally Posted by Jim 99 eldo View Post
    Jake at what % of the OLM do you suggest performing a drain?
    Jake's not here right now - remember that he said that 90% of his recent mileage was at highway speeds and loads. That type of driving is the easiest for any engine, so the OLM would creep down slowly. If your driving is in town exclusively, with idling and stop/start, the OLM will drop like a rock.

    I'll part ways with Jake on this aspect (and temper it because of the differences in pre-2000 engines) and say that the OLM works - for the oil formulation that the old algorithm was based on. Since the late 90's we've seen a decrease in oil additives - ZDDP if you will - so the algorithm may no longer be accurate for a pre-2000 engine. Either change your current SM oil/filter by the seat of your pants or (pre-2000 only) use a Fleet/Marine 10W-30 oil such as Rotella, Delo, or Long Life and go back to the OLM - those oils have very close to the same anti-scuff/anti-foam package as the (EPA mandated) obsolete SH/SJ oils of several years ago.

  11. #10
    Ranger's Avatar
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    Re: Cold Carbon Knock? Thought I ate another exhuast cam...

    I'm with Sub on this one. Here is what our old Guru (A GM powertrain engineer) had to say about the OLM. In the mean time, take it out and give it some good ole WOT. If that cures it, it's cold carbon rap.


    "One thing I can touch on and clear up.....the GM oil life monitor operation and my statement that ZDP (or ZDDP as you tend to call it here...most of the API literature just sticks to ZDP so I tend to use that) depletion is the basis for oil deterioration.

    My spelling is poor but ZDP stands for zinc dialkyldithiophosphate which , as it sounds, is an anti-wear compound comprised of zinc and phosphorus.

    ZDP is dispersed in the oil so as to be at a potential wear site if a surface asperity happens to break thru the oil film thickness causing the dreaded metal-to-metal contact. A molecule of ZDP must be present at that moment to prevent microwelding at the contact site which will cause material transfer, scuffing, scoring, wear and catostrophic failure. The concentration of ZDP in the oil will determine if there is ZDP present to work it's magic. The greater the concentration...the more likely a molecule of ZDP will be there...and vice versa.

    By nature, ZDP is sacrifical. As ZDP is "used up" at a wear site to prevent micorwelding the concentration of ZDP decreases.... So...if you measure the ZDP concentration in engine oil in a running engine it will decrease at linear rate based on engine revolutions. Any given engine has a certain number of high potential wear areas where metal-to-metal contact could occur due to reduced film thickness and/or surface asperities....areas such as rubbing element cam followers, distributor gears, rocker arm pivots, push rod tips, etc...... The more of these areas the more ZDP depletion. The more often these features come in contact the greater the ZDP depletion. That is why, generally speaking, ZDP concentration in the oil, for any given engine, will decrease at a fairly linear rate when plotted versus cummulative engine revolutions. The more times it turns the more contact the more chance for wear the greater the depletion. This is as much of a fact as I could quote ever and is really not speculation or anything. It is proven beyond a shadow of a doubt in many studies. That is why it is ONE of the basis for determining oil life remaining and why it is THE basic premis of the GM oil life algorithm. It is only ONE of the things that determines oil life...but it is the one thing that can be tied to engine operation in a linear fashion and estimated very accurately by accumulating engine revolutions via a counter.

    The GM engine oil life monitor counts engine revolutions and accumulates the number for the basis of the oil life calculation. It then adds deterioration factors for operating temperature, start up temperature, soak times, ambient, coolant temperature, etc... There are a LOT of factors that "adjust" or affect the slope of the deterioration but the fundamental deterioration is traced back to the ZDP depletion that is inescapable with engine revolutions. The specific rate of ZDP depletion is readily measurable for any given engine so that is the fundamental item that is first calibrated for the oil life algorithm to tailor it specifically to that engine.

    You would obviously like to get the oil out of the engine before the ZDP concentration gets so low that it is ineffective at being at the right place at the right time and preventing engine wear so that becomes the long term limit on oil life for that application.

    The other things that determine oil life such a acid build up, oxidation, petane insuluables such as silicon from dust/dirt, carbon or soot build up from the EGR in blowby, water contamination, fuel contamination, etc.... are all modeled by the multipliers or deterioration factors that "adjust" the immediate slope of the line defined by the engine revolution counter as those items can be modeled in other ways and accounted for in the immediate slope of the ZDP depletion line.

    The algorithm was developed over the course of many years by several lubrication experts at GM Fuels and Lubes, spearheaded by Doctor Shirley Schwartz who holds the patents (with GM) for the algorithm and the oil life montitor. I had the luck of working directly with Dr. Schwartz when the idea of the oil life monitor first progressed from the theoretical/lab stage to real world testing/development/validation. There were fleets of cars operated under all conditions that deteriorate the oil life for any and every reason and , thru oil sampling and detailed analysis of the oil condition, the algorithm was developed, fine tuned and validated to be the most accurate way invented yet to recommend an oil change interval by. As just one example, I have seen cars driven side-by-side on trips, one towing a trailer and one not, for instance, to prove the effectiveness of the oil life monitor in deteriorating the oil at a faster rate just because of the higher load, higher average RPM, higher temps, etc...and it works flawlessly.

    The oil life monitor is so effective because: it is customized for that specific vehicle/engine, it takes everything into account that deteriorates the oil, it is ALWAYS working so as to take into account THAT INDIVIDUALS driving schedule, and it tailors the oil change to that schedule and predicts, on an ongoing basis, the oil life remaining so that that specific individual can plan an oil change accordingly. No other system can do this that effectively.

    One thing is that I know personally from years of testing and thousands of oil analysis that the oil life algorithm works. There is simply no argument to the contrary. If you don't believe me, fine, but, trust me, it works. It is accurate because it has been calibrated for each specific engine it is installed on and there is considerable testing and validation of the oil life monitor on that specific application. NOt something that oil companies or Amsoil do. They generalize....the oil life monitor is very specific for that application.

    Oil condition sensors in some BMW and Mercedes products are useful, also. They have their limitations, though, as they can be blind to some contaminates and can, themselves, be contaminated by certain markers or constituents of certain engine oils. Oil condition sensors can only react to the specific oil at that moment and they add complexity, cost and another potential item to fail. One other beauty of the GM oil life monitor is that it is all software and does not add any mechanical complexity, mass, wiring or potential failure mechanism.

    There is considerable safety factor in the GM oil life monitor. Typically, I would say, there is a 2:1 safety factor in the slope of the ZDP depletion curve....in other words, zero percent oil life per the ZDP depletion is not zero ZDP but twice the concentration of ZDP considered critical for THAT engine to operate under all conditions reliably with no wear. This is always a subject of discussion as to just how low do you want the ZDP to get before the oil is "worn out" if this is the deciding factor for oil life. We would tend to be on the conservative side. If the oil life is counting down on a slope that would recommend a 10K change interval then there is probably 20K oil life before the ZDP is catostrophically depleted....not that you would want to go there...but reason why many people are successful in running those change intervals.

    Please...NOT ALL ENGINES ARE THE SAME. The example above is an excellent practical justification of why you would want to add EOS and change the 15W40 Delvac in the muscle car at 3000 miles max and yet can run the Northstar to 12500 easily on conventional oil. You must treat each engine and situation differently and what applies to one does not retroactively apply to others. This is where Amsoil falls short in my book by proposing long change intervals in most everything if you use their oil. It just doesn't work that way. You can run the Amsoil to 12500 with no concerns whatsoever in the late model Northstar because even the oil life monitor tells you that for conventional oil off the shelf. Would I do that to the 502 in my 66 Chevelle...NO WAY. Amsoil says I can though. Wrong.


    There are entire SAE papers written on the GM oil life monitor and one could write a book on it so it is hard to touch on all aspects of it in a single post. Hopefully we hit the high spots. Realize that a GREAT deal of time, work and energy went into developing the oil life monitor and it has received acclaim from engineering organizations, petroleum organizations, environmental groups all across the board. It is not some widget invented in a week and tacked onto the car."
    Tom99STS and Tom99STS like this.

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