block test, throttle body cleaning, and coolant flush and conversion
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, block test, throttle body cleaning, and coolant flush and conversion in Past Cadillac Vehicle Discussion; Hey guys. Just wanted to share my positive cooling system flush and conversion to green antifreeze experience. I have a ...
  1. #1
    Lunchbox7688's Avatar
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    block test, throttle body cleaning, and coolant flush and conversion

    Hey guys. Just wanted to share my positive cooling system flush and conversion to green antifreeze experience. I have a 99 concours with only 87,xxx on her. Let me say that through all of this the head gasket was in the back of my mind! A couple months ago I changed the water pump simply because the o-ring gasket behind it was seeping. I smelt coolant over there ever since, but couldn't find it leaking. I'm driving her to Tennessee from Wisconsin and back in 2 weeks so I figured I better fix the smell. I let her idle for like 45 minuets so I could watch every angle at all temps, and she started to really heat up. Way high! All I kept thinking was "oh no, head gasket"! I shut her off and referenced my dealer service manual. I ran to the store and rented a block tester. I let her cool down and tested her over and over like 7 times until I ran out of the fluid and it never turned yellow. Giant relief!!!!!! I know the big controversy over dex-cool and wanted to change to conventional anyway so I drained the coolant and started flushing the system. Not long into disassembly I found brown sludge! I found a couple plugged passages. That was good news to me! It would explain the overheating. I kinda went all OCD and took off the throttle body and whole coolant crossover piece. I was able to really get in there with the hose and flush it all out. I even cut the upper heater core hose and installed a flushing tee so I could flush it even more. When I removed the coolant crossover, I found that 2 of the 4 gaskets were deteriorated, bad. I don't think they should have been that bad with only 87,xxx. Probably another symptom of not maintaining the northstar, just like the sludge I found. I also cleaned the throttle body like I read in a thread in here. It was filthy! I will be taking the intake manifold off for a good cleaning as soon as I get back. I put her back together with all new gaskets and nice fresh green antifreeze and she's running like a champ! It took me 2 slacker days, it was not hard at all, and now I can sleep at night knowing my baby is all good again. Just a weird note. In my dealer service manual (I have all 3 volumes), in the recommended fluids section, it states to NOT use the sealant pellets. Everywhere else I read in all the volumes it says to use the pellets. Weird.

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    MoistCabbage's Avatar
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    The sludge you found was sealant tab residue, it's known to clog small coolant passages. GM no longer uses or recommends them.

    Weather you use DEX or "the green stuff" is irrelevant, they'll both do the same thing just as well, and either should be drained and replaced every 2 years, 3 max. A flush is not necessary.

    Crossover gasket failure is not uncommon, and age is more of a factor than mileage.

    Did you check/clear out the purge line?

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    Lunchbox7688's Avatar
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    She IS 14 already. Lol. Ya the purge line was clear cause when it started to overheat the coolant was pissing out of the tube pretty good. I was super relieved it was just normal coolant issues.

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    Re: block test, throttle body cleaning, and coolant flush and conversion

    Quote Originally Posted by Lunchbox7688 View Post
    I will be taking the intake manifold off for a good cleaning as soon as I get back.
    Don't waste your time. There is no way to clean the intake and even if you could, it would have no effect. The oily mess inside is disgusting, but normal and harmless.

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    Re: block test, throttle body cleaning, and coolant flush and conversion

    Forget the intake manifold cleaning - the coating is condensed oil vapor from the PCV system. Normal, and our engines use port injection so the intake valves and inner ports are constantly washed by fuel spray. Not a problem. If you're truly antsy about a little oily coating, buy another (new) manifold and seal set - they're not expensive - and then, at your leisure, you could have the original hot-tanked at an engine overhaul shop.

    To further fuel your coolant paranoia, Prestone (a DEX-COOL supplier to GM) now has a yellow (not yellow-orange) coolant that is completely universal - it can be used with or to substitute for any coolant on earth.

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    Re: block test, throttle body cleaning, and coolant flush and conversion

    Quote Originally Posted by Lunchbox7688 View Post
    She IS 14 already. Lol. Ya the purge line was clear cause when it started to overheat the coolant was pissing out of the tube pretty good. I was super relieved it was just normal coolant issues.
    -------------------------------
    Ya the purge line was clear
    cause when it started to overheat
    the coolant was pissing out of the tube pretty good.

    that sounds like the OVERFLOW hose -
    NOT the PURGE LINE -

    the PURGE LINE is how the Northstar motor eliminated air from the cooling system -

    there should be a gentle - constant flow of coolant -
    anytime the engine is running -

    you should double-check it - just to be sure -

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    Re: block test, throttle body cleaning, and coolant flush and conversion

    Here you go .......... Deville coolant reservoir - as always, when all else fails, read the fine print and study.

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    Ya I guess it would be pretty hard to get my hands in the intake and clean it good. I did used the prestone universal. I knew the gm approval for them for the dex, so that's why I used it. The stuff I used was green though.

    ----------

    My reservoir is a little different. But that purge line in your pic looks like the same line that goes all the way across the motor and through the throttle body and through that bolt into the coolant passage. That bolt was plugged up with sludge. That's why I freaked and tore apart the cooling system. If that's the purge line, then it was plugged and it's definitely clear now. Lol

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    Re: block test, throttle body cleaning, and coolant flush and conversion

    No "if". That's the purge line, a critical part of ANY divorced coolant reservoir cooling system. (NOT a "coolant recovery tank" which operates at atmospheric pressure.)

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    That line being plugged would explained how the coolant reservoir was acting while she was overheating (lots of air bubbles). Anyway, I've already put almost 100 miles on her in the past 2 days. Stop n go, freeway, and idling and she never went over 207 degrees (I changed option E to get the digital temp readout on my analog dash). I think she's all good now!

  12. #11
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    Re: block test, throttle body cleaning, and coolant flush and conversion

    If you drive around with the HVAC system set to some function that uses the A/C compressor, cooling fans run in SLOW all the time and, except in the worst summer traffic jam, you should see the coolant temp stay around 190 - 210. With no A/C compressor function set (OFF or ECON) then the fans are controlled by the ECT sensor - in slow traffic the engine will heat to 224, fans come on in SLOW, coolant drops to 213, fans turn off and the cycle starts over. Normal.

    In extreme heat and traffic conditions fans may go to FAST at 236. Good 50/50 coolant, pressurized to 16 or 18 psi, boils at ~267 degrees F.

    Sooooooooo ................. Don't go paranoid if your temp gauge or readings rises and falls with engine operation during different conditions.

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    Good to know man. Thanks. I'll use that as a guideline now.

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    Re: block test, throttle body cleaning, and coolant flush and conversion

    There are two sticky posts on this cooling system operation subject in the Engines; Northstar Performance forum, as well as information up ^^^ in the top black bar - Cadillac Technical Archive ...... Important info there for ANY Northstar driver.

    Always read the stickys in each forum as well as threads of interest in Discussions, Item Specific: Cadillac Tech Tips.

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