1999 STS rear level control
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 1999 STS rear level control in Past Cadillac Vehicle Discussion; Hey guys, First off i am new to Cadillac forum, so hello. needing a little guidance or advice. my parents ...
  1. #1
    99slvrcaddy is offline Cadillac Owners Member
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    Cool 1999 STS rear level control

    Hey guys,

    First off i am new to Cadillac forum, so hello. needing a little guidance or advice. my parents recently picked up a 99 sts with 80k miles. my dad had me take it into a shop today for a coolant flush, well after driving it today the coolant temp gauge moves around very erratically. it will shoot up like its getting hot then return back to the middle which is where it had stayed the whole trip home. when i pulled into my drive way i let the car idle for a min and watched the temp gauge. it was bouncing around a little. then it pegged completely on the hot side and warnings came up everywhere for about 1 sec. then returned to the middle line on the temp. car doesn't seem to be over heating. do you guys think this is head gaskets or is it most likely a faulty gauge or sensor or air in the system? whats the best way to eliminate things?


    second, the rear end of the car is sitting really high like a dragster. looks pretty funny. the air compressor kicks on every time when the key is cycled for about 5-10 sec. its almost like its not letting air outta the shocks. any suggestions on what to check? some kind of valve or something and where is it located? it looks like factory shocks. and there is no dtc codes when checked for the air ride.



    any info is appreciated! thanks!

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Need guidance please!!

    The cooling system probably has trapped air in it - do a search for the coolant purge line and hollow bolt/nipple and how to check for proper purge line flow. It's all in here and in the stickys in the Engines, Northstar Performance forum. Google "cadillac forums 1999 seville coolant purge line test".

    The car does not have air ride. They have ELC/ALC (Electronic/Automatic Level Control) depending on year/model. The compressor will always do a preload and prove-out shortly after key: ON. If the rear is not sitting so as to give the car a VERY slight rake, then there's a problem with the compressor exhaust solenoid head.

    Get 2 assistants and do this test ........ Pop the trunk. Turn the Key: ON and listen for the prove-out. OK ? leave the key on and y'all sit on the open trunk lip. The compressor should run and level the rear. OK ?? All hop off and you listen in the RR wheelwell for escaping air - as the solenoid exhausts air from the shock bladders and again levels the rear. OK ??? If not, you have compressor assembly (compressor/solenoid head/filter-dryer) problems.

    Cadillac Tech Tips search or Google "cadillac forums 1999 seville rear level control compressor" or something close.

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    Re: Need guidance please!! 1999 STS rear level control

    Yeah, check that purge line. Hopefully that's all it is.

    One more thing. Keep an eye on the coolant level. It can take a couple of days to stabilize depending on how well it was drained. Correct level is about 1/2 full (no less).

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    99slvrcaddy is offline Cadillac Owners Member
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    Re: Need guidance please!! 1999 STS rear level control

    Thanks for the response! I went out this morning and popped the top off the coolant resivour and they filled the resi all the way to the top. Obviosly that's over filled! So does it need to be at the line under the arrow that points down on the resi? And would that cause it not to self bleed?

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    Re: Need guidance please!! 1999 STS rear level control

    Quote Originally Posted by 99slvrcaddy View Post
    Thanks for the response! I went out this morning and popped the top off the coolant resivour and they filled the resi all the way to the top. Obviosly that's over filled! So does it need to be at the line under the arrow that points down on the resi? And would that cause it not to self bleed?
    ---------------------------------
    the proper level is about half full as shown on the side "FULL COLD" -
    -----------------------

    the PURGE LINE is the only way of expelling air from the Northstar cooling system -

    it is a 3/8 diameter hose that goes from a hollow bolt in the thermostat/waterpump housing area of the engine - and plugs onto a nipple on the side of the SERGE TANK -

    with the engine running - there should be a gentle - constant flow of coolant - from the engine - to the serge tank -

    if there is no flow - the most likely cause is a blockage in the hollow bolt -

    follow the hose towards the engine - with the engine OFF - remove the hose - use a straightened metal coat hanger - or something similar - and poke it into the hollow bolt -

    the coat hanger should go in about 2 1/2 inches -

    once the hollow bolt is cleared - you can briefly start the engine to verify coolant flow - be sure to use some sort of container to catch the coolant so you don't make a mess -

    check the hose and serge tank for bloc

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    99slvrcaddy is offline Cadillac Owners Member
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    Re: Need guidance please!! 1999 STS rear level control

    Ok so I took the hose off the serge tank and there was no flow, so then took the other end off and stuck a metal wire down there a pretty good ways. Still no flow at all! Does the engine need to be hot to verify this and the cap on or will it flow w the engine cold?

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    Re: Need guidance please!! 1999 STS rear level control

    Quote Originally Posted by 99slvrcaddy View Post
    Ok so I took the hose off the serge tank and there was no flow, so then took the other end off and stuck a metal wire down there a pretty good ways. Still no flow at all! Does the engine need to be hot to verify this and the cap on or will it flow w the engine cold?
    -----------------------------------------------
    Does the engine need to be hot to verify this
    and the cap on or will it flow w the engine cold?

    NO -
    any time the engine is running
    there should be coolant flowing through the PURGE LINE -

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    Re: Need guidance please!! 1999 STS rear level control

    If the shop filled the coolant to the top of the tank, put them at the top of your shit list and never go back.

    You could suck it down to 1/2 - 2/3 or just let it puke out the excess and find it's own level. Just don't panic if you see coolant on the ground once or twice.

    Do you get any flow out of the purge line if you rev the engine a bit? Best to be doing this with a cold engine for obvious reasons.

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    99slvrcaddy is offline Cadillac Owners Member
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    Re: Need guidance please!! 1999 STS rear level control

    There was no flow coming through the serge tube at all even with the car running. And nothing is moving in the coolant resi w the car running. No bubbles or anything. Also idk what u mean by hollow bolt? This looks like a metal tube that goes under the intake that is connected to the surge line? Any more suggestions to clear blockage or something, I'm lost on why I'm not getting anything flowing through that

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    Re: Need guidance please!! 1999 STS rear level control

    Follow the purge line from the nipple on the surge tank to the hollow bolt/nipple at the water crossover/water pump housing cover.*

    With the engine idling, hot or cold, that line must flow a small steady steam of coolant - if you disconnect it from the surge tank nipple and hold the hose in the open filler neck.

    If there's no flow, either the rubber line is clogged or the hollow bolt/nipple is clogged. Either clear the purge line or replace it with a proper sized length of fuel hose (will carry cooling system pressure) from any car parts store or, if the line is clear, rod out the hollow bolt/nipple.

    Proper coolant level is halfway up in the surge tank, cold - NEVER check or adjust coolant levels with the engine hot.

    *Your engine may have a coolant heated throttlebody bore. In that case, the purge line connects to the throttlebody tubes, then to the surge tank nipple. Bypass the throttlebody. Run a new purge line, with a bit of slack, directly from the hollow bolt/nipple to the surge tank nipple.

    Look in my albums to see the hose run.

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    Re: Need guidance please!! 1999 STS rear level control

    Quote Originally Posted by 99slvrcaddy View Post
    There was no flow coming through the serge tube at all even with the car running. And nothing is moving in the coolant resi w the car running. No bubbles or anything. Also idk what u mean by hollow bolt? This looks like a metal tube that goes under the intake that is connected to the surge line? Any more suggestions to clear blockage or something, I'm lost on why I'm not getting anything flowing through that
    --------------------------
    OK - once again - with more feeling -

    you have a SURGE TANK -
    the thing some people improperly call a coolant reservoir - or overflow tank -

    on the top of the SERGE TANK is the pressure cap -
    near the pressure cap is the OVERFLOW HOSE -

    on the SIDE of the SERGE TANK is a 3/8 diameter hose
    that goes to the engine thermostat/waterpump housing -
    THAT is the PURGE LINE -
    it might be rubber - it might be metal - it might be both -
    but it is the ONLY piece of tubing
    that goes between the SIDE of the SERGE TANK -
    and the engine -

    at the engine - the PURGE LINE attaches to a hollow bolt -
    that is screwed into the thermostat/waterpump housing -

    the HOLLOW BOLT is usually what plugs up -

    any time the engine is running -
    there should be a constant - gentle flow of coolant -
    running FROM the engine - TO the SERGE TANK -

    if there is no coolant flowing through the PURGE LINE -
    there is a great possibility - or rather PROBABILITY -
    that you have some air trapped in the cooling system -
    and an air pocket could stop the flow of coolant through the motor -
    and cause overheating -

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    Re: Need guidance please!! 1999 STS rear level control

    Here is the "hollow bolt" that the purge line is attached to (U shaped hose with the spring clamp is attached to it). If you have no flow from the purge line under any RPM, then either it is clogged or you have "air" in the cooling system.
    Attached Images

  14. #13
    stoveguyy is offline Cadillac Owners Connoisseur
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    GM redid the coolant crossover around 98 or so? Changed the TB mounting so it has different heat transfer characteristics? My 96 has the heated TB coolant loop. Will bypassing it be an issue in the winter? Why does GM think heating the TB is necessary? It is emissions related or cold weather driving?

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    Re: Need guidance please!! 1999 STS rear level control

    I think the heated TB is to prevent possible icing and thus a stuck open throttle. Not sure I see the logic behind that since there is no venturi to cool the incoming air. Since other models do not have the heat, I seriously doubt you'll have any winter issues.

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    Re: 1999 STS rear level control

    The theory goes that, at partial throttle blade openings, the pressure differential across the butterfly causes a radical venturi effect at the throttle blade edge (in this case, that is accompanied by a large air temperature drop across the atmospheric pressure/vacuum change at the blade edge). During spring/fall humid morning/evening starts/slow speed driving that pressure drop could - could - cause TB bore icing. (It happens in recip aircraft engines all the time, thus the "carburetor heat" cable). Venturi icing is common in carburetor applications - thus the old GM "Thermactor" warm air diverter doors in the air cleaner intake snout.

    Our throttlebodies are bolted directly to the coolant crossover casting - which is hot by design. I seriously doubt whether bypassing the coolant loop on the pre-2000 models will have ANY effect on TB bore icing.

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