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Thread: Yet More Cooling System Fun

  1. #1
    Join Date
    Dec 2007
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    Yet More Cooling System Fun

    After doing head gaskets (and lots of new cooling system parts) exactly 12 months ago, after which the cooling system in my Anny was well behaved without fail, I went to buy gas a few days ago, 80° out, and sat in line for a short while waiting my turn w/the engine running, A/C off. Noticed the coolant temp climbing higher than it should, past M (usually not past O|R)...fan finally came on, no drama, but not good. Got home, noted the coolant level in the expansion tank was past HOT and started checking why.

    No fail w/the fan, just that it was coming on late. No leaks, no bubbles in the expansion tank, no codes, radiator cap/IRCM/thermostat/both fan speeds all checked good...hoped it wasn't another head gasket so did a combustion-gas-in-the-coolant test which came up negative.

    Volts in/out at the ECT seemed off given the heat that it took before the fan came on, but it's connector was clean and a new sensor didn't help. I moved up the harness to the large grey main harness multi-wire connector (C172?) back near the self-test connector & ABS relays (while wondering if maybe the ECU was borked) to check ref. signal at the connector with it open so I could lay eyes on pins. Bingo...green means stop.

    Name:  SC_HarnessECT.png
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    Cleaned everything up, reconnected, problem solved, signals dead on specs at ECT. Looks like the signal was off enough to cause late lo speed turn-on, but not enough to throw a code. Time to start checking every connector I can reach that I know hasn't been opened/inspected in the last few years...or more.
    Last edited by KMT; 08-28-2019 at 09:46 AM.

  2. #2
    Join Date
    Nov 2012
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    Canton, GA
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    My 1990 SC (not the one I changed head gaskets on) keeps creeping up to the "M" in "NORM" so I may investigate its wiring too. I just bought a head gasket tester kit for my new-to-me 1993 SC, I may just line up all 3 of my SC's and give them the test in a single afternoon for peace of mind. Might even run a pusher fan to all of them because I am sick of overheating problems

  3. #3
    Join Date
    May 2012
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    Denver Area
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    I was an avionics technician in a previous life in the US Navy. Gunk, corrosion and dirt wreak havoc on electronics and connectors. When you operate in a salt air ocean environment you clean exposed connectors every seven days and do deep cleaning on a 28 day cycle. It makes perfect sense to clean the connectors on our cars after 25 years. One thing I've noticed since I continue to learn about my SC is that the entire system is interconnected in terms of sensors, Voltages and the PCM. I had a particularly annoying issue here recently that came down to the Engine Coolant Temperature sensor that the PCM reads to know water temp (not the gauge sender). Now that I have the correct thermostat installed with the correct ECT everything works exactly as designed - even up here in high altitude hot Denver summer days at 95 degrees. For some reason after I've got my main issues cleaned up my transmission is shifting much better. I have no idea why unless it was temperature related.

  4. #4
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    The black round connector* that sits on the same bracket, next to the grey one in the photo, had green too. When I did the ABS relays that sit further back, last year, the one for the pump was pretty bad.

    It makes perfect sense to clean the connectors on our cars after 25 years.
    Tired of finding corrosion after the fact, I'm putting mine in a 2yr. re-check schedule, nose to tail (excluding the cabin unless I find cause). Living in Oregon doesn't help, I'm sure you know.

    *Speaking of interconnected, that connector carries the wire that feeds 5V ref. to the ECT, ACT, TPS, BAP, knock sensor, and EGR transducer (where applies), along with wires that involve the O2 sensors and injectors. Individually you could chase stuf for days, but if those circuits are compromised, no telling what system will act up.


    Glad you sorted your trans, good luck w/it.

    Ken
    Last edited by KMT; 09-20-2019 at 09:27 PM.

  5. #5
    Join Date
    Jul 2019
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    6

    head gasket tester kit? What's that and where do i get one?

    head gasket tester kit? What's that and where do i get one?

  6. #6
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    Jul 2019
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    160 deg thermostat

    Is a 160 deg thermostat ok or to cool?

  7. #7
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    Quote Originally Posted by djs56 View Post
    head gasket tester kit? What's that and where do i get one?
    It’s technically called a Combustion Leak Test Kit; here is the one I got.
    I haven’t used mine yet, but it looks pretty straightforward.

    https://www.amazon.com/Block-Tester-...a-570352767565

  8. #8
    Join Date
    Jul 2019
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    Amazon has almost everything. And yes it looks farly easy to use.
    Thanks

  9. #9
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    Quote Originally Posted by djs56 View Post
    head gasket tester kit? What's that and where do i get one?
    It's a kit that checks for exhaust gases in the coolant. On an SC, you'd get the car up to temperature and use the tester on the expansion tank's opening.

    You can buy a kit off eBay, etc. Search for: cooling system combustion leak tester

    Or you can rent one from AutoZone for free...they just put it on your credit card, then back the charges out when you bring it back.
    Last edited by KMT; 08-28-2019 at 10:56 PM.

  10. #10
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    Quote Originally Posted by djs56 View Post
    Is a 160 deg thermostat ok or to cool?
    Way too cool. The SC's 3.8L V6 relies on much higher coolant temps to operate normally.

    Some owners run lower temp stats, say 180, but they use a chip so they can tune the fans to work at a different temperature. My advice is that unless you know what you're doing and have a tune on your car, do not get creative, and stick with the stock 192° thermostat. If your SC is overheating, fix the issue(s), don't cater to it.

  11. #11
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    Great job tracking it down. I checked those last year when doing work on the ABS system for my 35th. I ended up using both NOS relays, but I have a feeling it may have been a question of dirty connectors at the relay base (mine looked much worse than yours). Mind you, this was on a car with less than 60k miles at that point. In any case, cleaned everything I could at that time since I had the spray cleaner out. All our connectors are bound to be gunky after almost 30 yrs.
    Current: 1993 SC 5.0L Auto Red, 1994 SC 5-speed Teal, 1995 SC 5-speed Chameleon Blue
    Old: 89 SC auto Twilight Blue, 89 SC stick Titanium, 90 35th stick, 92 Sport 5.0L stick, 94 SC stick Black, 1994 SC Auto Teal
    Also: 1992 Feature Mustang Convertible 5-speed Vibrant Red, 1991 BMW 850i 6-speed Red, 1994 BMW 850CSi 6-speed Red

    www.mamn12.com for your mid-atlantic mn12 needs!

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