Pressure in expansion tank
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Northstar Engines and System Technical Discussion Discussion, Pressure in expansion tank in Cadillac Engine Technical Discussion; Regardless of possible N* issues, I'm seriously considering buying a lowish-mile (under 100K) 98-00 DeVille. I've read quite a lot ...
  1. #1
    TexFinn is offline Cadillac Owners Fanatic
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    Question Pressure in expansion tank

    Regardless of possible N* issues, I'm seriously considering buying a lowish-mile (under 100K) 98-00 DeVille. I've read quite a lot about the HG issues over the years as I also owned a 97 Eldorado a few years ago. That had had the HGs and other related things fixed, so I could breathe a little easier...

    I drove a 78K mile 98 DeVille today and it prompted some concerns in my mind. No milky residue on the oil cap and no visible oil in coolant. Coolant temp went to about 255F while driving, but I guess that's still okay, right? Coolant was orange in color, so I'm assuming DexCool is being used.

    The main thing that concerned me a lot was that there was huge amount of pressure in the expansion tank and there was a lot of coolant draining from the overflow tube. When I loosened the cap slightly, the coolant started pouring through the overflow tube almost like if you'd open a faucet fully at your house. I mean, of course there is pressure in the system, but so much that it pushes the coolant through the overflow tube? And I don't think it was really overfilled, either...

    Is this kind of pressure something to be concerned about? Heater worked fine (couldn't get airflow through the center or floor vents, though), AC worked, most of the electronics also worked properly, no SES/ABS/airbag etc. lights on and it only has a few cosmetic issues to tackle.

    Thank you in advance for any and all info and advice you guys could provide! Any hints/tips as to what to check/do are also appreciated.

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    MoistCabbage's Avatar
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    Northstars don't typically mix coolant with oil, smoke, or develop milky residue I'm the oil cap as a result of HG issues.

    DEX-COOLis irrelevant.

    255 is definitely not normal. 195-210 is closer to normal while driving.

    A clogged purge line could cause elevated temps, but I would do a block test before considering buying the car.

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    TexFinn is offline Cadillac Owners Fanatic
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    Re: Pressure in expansion tank

    Thanks for the comments! Guess I need to refresh myself a little bit on the symptoms of a failed HG in the N*...

    195-210, huh...? Guess it was running a bit hot, then. Would a clogged purge line also cause the seemingly excessive pressure in the expansion tank? I mean, that coolant really shot out of that overflow tube like it came from a house faucet...

    Doing a block test is a bit challenging since the seller lives pretty much in the middle of nowhere and there really are no shops around... With the car being otherwise in pretty good shape and having low miles, I wonder if it would be worth 1400-1500 gamble to buy it....?

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    MoistCabbage's Avatar
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    Even an otherwise immaculate '98 with HG issues isn't worth more than $1K. You can get a block test kit from most parts stores through their loan a tool program. All you have to actually purchase is the test fluid, ~$10.

    There's really no way to tell if the pressure in the tank was excessive, or if the cap is just bad, without a pressure test kit. That said, coolant being purged AND overheating aren't a good sign.

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    Re: Pressure in expansion tank

    RUN, don't walk away from that car.

    Regardless of possible N* issues, I'm seriously considering buying a lowish-mile (under 100K) 98-00 DeVille.
    Go for a 2000+. Stay away from the '98 & '99's.

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    Re: Pressure in expansion tank

    You can perform a cylinder block exhaust gas test at the top of Mt. Everest. Simple apparatus, rented from any large parts store. The test set measures exhaust gas components in the airspace over the coolant in the surge tank. Any coolant enters the test fluid and you wash everything and start over.

    Heed the advice on a '98/'99 Northstar that you cannot absolutely document recent, proper head gasket repair on. If the deal is too good to be true, it is for a reason ............

    http://www.sjdiscounttools.com/lis75500.html

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    TexFinn is offline Cadillac Owners Fanatic
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    Re: Pressure in expansion tank

    Quote Originally Posted by Ranger View Post
    RUN, don't walk away from that car.

    Go for a 2000+. Stay away from the '98 & '99's.
    Yeah, decided to forget about that one. Too many unsure things with it.

    The problem with 2000+ is that I don't like the way they look. I like the updated oldschool-ish look of the 97-99 models.

    Search continues...

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    Re: Pressure in expansion tank

    You're foregoing a LOT of engine and suspension improvements by sticking with a pre-2000 model. The 98-99 were very close (almost identical) to the 2000 and later look, but had the worst problems with cylinder blocks and head bolts.

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    drewsdeville is offline Cadillac Owners Master
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    Re: Pressure in expansion tank

    The OP is looking at Devilles. There are large, fundamental changes between the pre and post 2000. Two styles with completely different personalities.

    To a gearhead or anyone that opens the hood, the nitty gritty 2000+ updates might be worth something - maybe even enough to make sacrifices in other areas as suggested. But to most, said updates are probably irrelevant. The changes aren't anything Joe Shmoe will notice or care about from behind the wheel. As far as the engine - New heads, rollers, COP ignition, this moved over here, that moved over there... who cares? Both versions deliver a near identical driving experience (same power , same mileage). Silly to consider a different vehicle based on such (relatively) petty changes.

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    TexFinn is offline Cadillac Owners Fanatic
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    Re: Pressure in expansion tank

    Yeah, Deville is what I'm looking at. Among some other vehicles, that is... Not really a big fan of Sevilles.

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    Re: Pressure in expansion tank

    Cost, features and looks being qualifying factors, I would buy a 98 or 99 model at the best possible price based on drewsdeville's advice.

    I said nothing about Sevilles...... strictly mechanical/electronic developments in the pre/post-2000 model year Cadillac FWD changeovers.

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    Re: Pressure in expansion tank

    The BIG difference between the pre 2000's and the 2000+'s is the HG reliability factor.

  14. #13
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    Re: Pressure in expansion tank

    That's apparently not a factor in this thread's buying decision process - appearance is.

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    TexFinn is offline Cadillac Owners Fanatic
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    Re: Pressure in expansion tank

    If I don't like the styling of the 2000+ models, then I will not consider them. Even if they have better HG reliability.

    I could buy also a -insert here a name of a brand with good reliability-, too, but if I don't like the way they look, then it's a mo go. Like it would be for most other people, too.

    Thank you for all the comments, though.

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    Quote Originally Posted by TexFinn View Post
    If I don't like the styling of the 2000+ models, then I will not consider them. Even if they have better HG reliability.

    I could buy also a -insert here a name of a brand with good reliability-, too, but if I don't like the way they look, then it's a mo go. Like it would be for most other people, too.

    Thank you for all the comments, though.
    The only thing i dont like about the 00-02 models is the lack of chrome trim on the sides and bumpers

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