98 STS White smoke on accelation
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Northstar Engines and System Technical Discussion Discussion, 98 STS White smoke on accelation in Cadillac Engine Technical Discussion; Hi, I have been reading through threads for the better part of the day and have found similarities in many ...
  1. #1
    lcryan is offline Cadillac Owners Member
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    98 STS White smoke on accelation

    Hi, I have been reading through threads for the better part of the day and have found similarities in many others problems, though nothing exact.
    I have a 98 STS Northstar 32 with 110k miles.
    For a while now I got an occasion small puff of smoke while on the highway. Unnoticeable to me but when someone was following me they'd inform me. On my latest trip I discovered that while doing ~65 mph, when I released the throttle and then went back on I got a large cloud of white smoke. The smoke smelt like the exhaust from a boat engine is the best way i could describe it. I noticed it did not happen every time but was more prevalent when I released the gas allowed the car to slow and then gave it gas.

    While I throttled and even up hills pushing the engine I got no smoke. I have thus far had no problems with overheating my gauge is pinned on 12:00. The oil was not milky and the coolant level was fine. Transmission fluid was slightly overfilled, but nothing I saw a problem with.

    Any and all thoughts would be greatly appreciated!
    Thank you to the community for your help.

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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 98 STS White smoke on accelation

    Sounds like oil. Valve seals maybe.

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    Submariner409's Avatar
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    Re: 98 STS White smoke on accelation

    Valve seals, stuck compression rings. When under coastdown conditions, intake manifold vacuum increases radically, literally sucking oil up the cylinder wall/piston sides due to the vacuum.

    Go up to the Cadillac Technical Archive in the black bar and STUDY the articles on Northstar oil consumption and "Occasional full throttle operation is good..................".

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    tateos's Avatar
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    Re: 98 STS White smoke on accelation

    I agree with Sub and Ranger, but would like to add 1 more likely cause. The pre 2000 engines had the PCV gases enter the intake manifold near the throttle valve - I don't remember where it is on the 2000+. These blow by gases also contain small amounts oil vapor that condense and collect in the low spots of the intake manifold over time. If the throttle is closed, and then you suddenly open the throttle, especially WOT, after a period of days or weeks of not doing that, you will create a stronger than normal flow of air through the intake manifold that will sweep or flush out some of that condensed oil in the intake manifold. That will produce some smoke that you may or may not see in the rear view mirror, but only once or twice, for a few (5-10?) seconds - then the exhaust should appear normal. If your exhaust repeatedly emits a puff of smoke when apply the throttle after coast down, then I would suspect valve guide seals...although they are very good on the Northstar engines. Smoke on start up when idling, after being off for 30 minutes or more also points to bad valve guide seals.

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    Submariner409's Avatar
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    Re: 98 STS White smoke on accelation

    The pre-2000 Northstars send the PCV dirty air to the top of the throttlebody casting, on the vacuum side of the throttle blade.

    The 2000 and later engines send the PCV dirty air to the center of the intake manifold, through a formed pipe from the PCV orifice to the passenger end inside the manifold tunnel.

    Years ago AJXTCMAN did a thread titled "A river runs through it" - referencing the oil control baffle in the rear (right) cam cover of a pre-2000 Northstar and what happens to oil consumption when that baffle comes loose. It's all still in here.

    YES, bad valve stem seals will emit a puff of smoke on startup and maybe some on coastdown. Bad piston rings will emit smoke only during and after coastdown, engine running. BUT, oil smoke is definitely blue - not white.

    Oil = blue
    Gas = black
    Coolant = white

  7. #6
    foxjohnc is offline Cadillac Owners Member
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    Re: 98 STS White smoke on accelation

    Do you ever have to add coolant to the engine? I have seen it on other northstars (including my 97 deville) and most of the time it ended being head gaskets. Coolant collects in the cylinders upon deceleration and then when you get on the throttle again it blows it out of the pipe. The white smoke smelling like boat exhaust really sounds like coolant escaping through the tailpipe. I have seen valve seals exibiting the same symptoms but "most" of the time the smoke is blueish. Sometimes the smoke is more white then blue even with it burning oil.

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    lcryan is offline Cadillac Owners Member
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    Re: 98 STS White smoke on accelation

    Yesterday I noticed a low coolant level indicator in the dash come on. I checked it and added about 1/4 a gallon to fill to top. This is the first I have done this in a little over a year. Last time it was about a cup to fill. Does this most certainly mean head gasket?

    Also after reading the article you suggested submariner, I was excited to jump on the throttle again like I did when I first got the car. However, I am nervous I will do more damage then good; the other day while driving around 60 I decided to give it a little test and floored it, I got an initial joint just like i remember it, but then another joint and a small deceleration that made me nervous so I released the throttle immediately. I looked in my rear view and saw a bit of smoke.

    I am wondering if it is wise to WOT or is it more likely I'll do more damage.

    Also I would like to add the other day I was running the car at idle after a oil change and the temp gage dappled just slightly over 12:00. I got in the car and drove around the block almost immediately upon beginning to drive the gage was back pinned at 12:00. Not sure if this has any connection to the head gasket problem.

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    Re: 98 STS White smoke on accelation

    IF you have a HG going, you can't do anymore damage.

    Also I would like to add the other day I was running the car at idle after a oil change and the temp gage dappled just slightly over 12:00. I got in the car and drove around the block almost immediately upon beginning to drive the gage was back pinned at 12:00.
    Driving it probably just purged the air out of the system. That's why the temp was up in the first place and then went down. That said, adding coolant is not normal. Something is amiss.

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    Re: 98 STS White smoke on accelation

    Quote Originally Posted by lcryan View Post
    Yesterday I noticed a low coolant level indicator in the dash come on. I checked it and added about 1/4 a gallon to fill to top (1).

    but then another joint (jolt ?) and a small deceleration that made me nervous so I released the throttle immediately. I looked in my rear view and saw a bit of smoke. (2)

    I am wondering if it is wise to WOT or is it more likely I'll do more damage. (3)

    Also I would like to add the other day I was running the car at idle after a oil change and the temp gage dappled just slightly over 12:00. I got in the car and drove around the block almost immediately upon beginning to drive the gage was back pinned at 12:00. Not sure if this has any connection to the head gasket problem.(4)
    1. Wrong. Coolant is only checked cold, and filled to the halfway mark in the reservoir - there's a FULL COLD legend and arrow molded into the reservoir top and side. Over full = blows coolant out of the reservoir on normal warmup. 1/4 gallon = 1 quart - the reservoir holds 3 quarts to the proper level.

    2. Smoke, carbon, crap out the exhaust pipe - perfectly normal for a car that is normally driven by a little old lady but is suddenly called upon to perform to it's potential.

    3. No. The engine is happy when it is dong its job.

    4. Your temperatures are perfectly normal. What "head gasket problem" ?

    Click on my username, open my profile. Two albums in there. 6 pages of stuff. Find the Northstar temperature gauge picture and study it.

  11. #10
    lcryan is offline Cadillac Owners Member
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    Re: 98 STS White smoke on accelation

    Quote Originally Posted by Ranger View Post
    IF you have a HG going, you can't do anymore damage.


    Driving it probably just purged the air out of the system. That's why the temp was up in the first place and then went down. That said, adding coolant is not normal. Something is amiss.
    In your opinion is it a HG? I have no had any overheating problems while driving what so ever.

  12. #11
    Submariner409's Avatar
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    Re: 98 STS White smoke on accelation

    Quote Originally Posted by lcryan View Post
    In your opinion is it a HG? I have no had any overheating problems while driving what so ever.
    Read Post #9 - matter of fact, read the entire thread again to put all this in proper context. The WORST thing you can do in a developing thread is lose sight of the first posts.

    The only way to confirm or deny a head gasket failure and subsequent exhaust gasses in the coolant is:

    www.sjdiscounttools.com/lis75500.html

    This ^^^ gets you your own tester. You CAN "rent" one from a large parts store, paying only for the test fluid, but some have had poor results with that store fluid itself.

    Please don't go paranoid ..............it's probably very unwarranted.

  13. #12
    Ranger's Avatar
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    Re: 98 STS White smoke on accelation

    Quote Originally Posted by lcryan View Post
    In your opinion is it a HG? I have no had any overheating problems while driving what so ever.
    Not at this point. I would add that if you are not overheating, IMO a block test is premature. It will most likely be negative.

  14. #13
    lcryan is offline Cadillac Owners Member
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    Re: 98 STS White smoke on accelation

    I did fill the coolant while cold. I brought it to a mechanic , he said it was most likely not the head gasket and replaced the MAF and the MAF sensor. I have noticed a significant decrease in white smoke, however when going through toll plaza (fast pass). I glided in from 65 down to ~35 and then accelerated and did notice another white cloud I left.

    Thank you guys for your continued help it is greatly appreciated.

  15. #14
    Ranger's Avatar
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    Re: 98 STS White smoke on accelation

    F.Y.I.
    A MAF and a MAF sensor are one in the same.

  16. #15
    Submariner409's Avatar
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    Re: 98 STS White smoke on accelation

    A significant question we've overlooked: Do you keep a close check on oil consumption, and if so, how much oil do you use every 1,000 miles ?

    (........and what oil viscosity and type are you using ?)

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