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Thread: wierd cooling issue....runs hot when driving but goes back to normal at stand still!?

  1. #1
    Join Date
    Dec 2010
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    wierd cooling issue....runs hot when driving but goes back to normal at stand still!?

    This is the story. My alternator went out. I did the autozone Mitsubishi alternator shuffle for about 3months until I found a used one on ebay for 60 bucks. Installed it with a new battery and everything works well. I also installed a new cam sensor and a new dis. But before this the car was jus sitting. After everything was installed and the car came back to life I let the car sit and run so all the new parts can configure themselves to the car. But I noticed when I turned the heater on it was blowing cold air even after like 45 minutes of idling it was ice cold in the car. So I drive the car around checking everything. I noticed the temp gauge was in the middle when it was idling. But when I drive the car down the road it begins to run very warm( check gauges and the check engine light came on) so I stop at the side of the road. I then realize the car was actually cooling off. After about 3min it retured to normal. No I'm super confused on the situation. So I drive it back home and on the way the heat decides to work. Which is a relief cause its freezing here in Detroit. As I drive I watch the temp gauge and it slowly creeps back up. And of corse when I park it the needle return to middle of the gauge.

    Please help. It doesnt seem like a water pump or radiator problem cause the car is ok at idle. One guy told me its the supercharger that doesn't sound like anything to do with my problem so I decided to come on here and get educated answer from you guys. Has anyone ever had this happen?

  2. #2
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    Change your thermostat. Sounds like its hung open. When your driving water wont stay in the radiator long enough to cool down. Thats also why your heater stays cold. Open thermostat is not forcing the water through the heater core, just letting it flow through the radiator.

  3. #3
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    Check to make sure the radiator is full. If you have air around the temp sensor it won't register, and having a lot of air in the cooling system will also cause problems with the heater running hot & cold. BTW, these are classic blown head gasket symptoms.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat.............10.597 @ 135.78

    My Garage

  4. #4
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    BTW, these are classic blown head gasket symptoms.

    David[/QUOTE]

    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    That would be my uneducated guess.

  5. #5
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    There is a vent for the cooling system to the left of the coil pack. It has a 13mm bolt w/a yellow printed piece of plastic around it. When you fill up the radiator, after you replace the thermostat, take that bolt out of the vent. Be careful not to break it. After the radiator's full, replace the bolt & see how that works. Just hope David's not right, head gaskets are a pain in the kabonza!
    1994 white sc (former Daily Driver)
    17 year sc owner
    SCCoA Member #: 3774

    View the car http://www.sccoa.com/forums/garage_v...vehicle&id=107

    UP THE IRONS!!!

  6. #6
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    Dec 2010
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    Well head gaskets aren't gone cause as I said b4 the car cools down on its own when sitting stationary.if the head gaskets were gone it would jus over heat all together, still or moving.plus no white smoke or fluid in the oil. I was thinking a thermostat and a radiator flushwould do the trick.

    What I have noticed is that anytime I give it some rpm's it tries to run hot. Then when I get off of it the temp goes back down to normal. When the heat does come on when I'm driving the temp does go back down a bit. But then the heat stops and the temp goes back up. I've never seen a car do this.

  7. #7
    Join Date
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    I'm thinking....

    With 35 degree's and drving... no heat
    Idle/parked heat comes on ...Thermastat. (no fluid loss)

    Heat On and Off as well as Heat Gauge... Burp the System (no fluid loss)

    Slow leak (driver side front intake manifold gasket)...slow leak looks like Head Gasket but different

    AntiFreeze pools in oil galley of block and shows no visible signs

    Paul

  8. #8
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    I do have a vacuum leak cause I'm only gettin like 11lbs. Of vacuum at idle. When I had the alternator installed the guy didn't seal the IC tube well. So I have a gasket kit coming, I bought a 180 degree thermostat. And I'm goin to burp the system tomorrow. I'll report back tomorrow with results.

  9. #9
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    Watch the 180 thermostat. Without a tune to change when the fan comes on you could still have cooling issues. May be better off with standard thermostat

  10. #10
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    Stuck thermostat sounds like a possible cause. But I would fear stuck closed more than stuck open. I wonder how much crud you will find in the cooling system when you open it up?

    Make sure you get the thermostat gasket for an SC - it has an extra hole.
    God bless!!!

    Former Birds:
    1990 SC auto ... red outside, gray cloth inside ... ~225,000 miles ... Sold.
    1990 SC auto ... white outside, gray cloth inside ... ~150,000 miles ... wrecked.
    1989 Base auto ... Crystal Blue metallic outside, dark blue inside ... ~160,000 miles ... Sold.

  11. #11
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    No chemicals except antifreeze in the radiator.

    If you flush it, don't use any chemicals to clean it it. That would be just asking for head gasket problems. Trust me I know.

  12. #12
    Join Date
    Nov 2012
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    19

    wierd cooling issue....runs hot when driving but goes back to normal at stand still!?

    Hey Turshin,

    my '95 SC did exactly the same thing after having the A/C compressor and everything replaced and charged back up. Replaced 2 O2 sensors, kept taking it back due to it creeping up as you also describe, mine always ran on the N on the Norm temp., when this was going on it started going to the M and a little past it. On the hiway it would run hotter, then in town it was back in the middle of the norm range. I kept taking it back telling them it was running too hot, they temp checked it said it was normal, etc...took it out on a hot morning, and had a major issue when coming home, it got hot, not into red zone ever, but on the almost the end of the norm range.

    Guess what it WAS head gaskets leaking, and it leaked into cyl #5, and i ended up having a bent rod. I just had the engine totally rebuilt, and got it back Monday. I would highly suspect your head gaskets are bad, and would stop driving it. Mine never ever smoked white, it never showed any coolant in the oil, or the bubbling up if you took of the radiator cap while running(i guess an old way to tell). None of these apparent signs were there, it just was getting too hot like yours is. I would err on the side of caution for sure, cause the rebuild is not cheap. Just my experience, and 2 cents. Goodluck
    Last edited by rd3; 11-15-2012 at 10:01 PM.

  13. #13
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    Quote Originally Posted by turshin View Post
    Well head gaskets aren't gone cause as I said b4 the car cools down on its own when sitting stationary.if the head gaskets were gone it would jus over heat all together, still or moving.plus no white smoke or fluid in the oil. I was thinking a thermostat and a radiator flushwould do the trick.

    What I have noticed is that anytime I give it some rpm's it tries to run hot. Then when I get off of it the temp goes back down to normal. When the heat does come on when I'm driving the temp does go back down a bit. But then the heat stops and the temp goes back up. I've never seen a car do this.
    This is a classic head gasket symptom. Dave is correct. Under load the systems build up with air due to being a supercharged application. You sit and idle, no more air entering the system. Some of the air bleeds off through the pressure cap and then she cools down.

    Don't discount people's feedback that have years of experience with these cars. You came here for help and this is what we try and do.

    Oh and BTW air in the system would cause heat issues as well. Again why head gaskets seem suspect. Forced induction cars do not operate under a vacuum under load.
    Last edited by 90sc35thann; 11-15-2012 at 09:54 PM.

  14. #14
    Join Date
    Dec 2002
    Location
    Omaha Nebraska
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    HG's

    Check your overflow container with the engine running. When my HG's blew, combustion gasses were getting pumped into the cooling system. Didn't burn coolant while driving, no coolant in the oil. If your gasket blew out, you will get massive amounts of bubbling in the overflow tank. This will give you all symptoms above. BTW, mine blew due to corrosion.
    JJ

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