Temp Sending unit mystery
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5.0 and 5.7 Discussion, Temp Sending unit mystery in Cadillac Engine Technical Discussion; Hi, well I had to post because I am not finding an answer in previous posts. This forum so far ...
  1. #1
    Goatspunk is offline Cadillac Owners Member
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    Temp Sending unit mystery

    Hi, well I had to post because I am not finding an answer in previous posts. This forum so far has been an excellent resource for problems that I've had.

    So I'm trying to install an aftermarket temp guage on my '91 Brougham Limo 5.7L 350. The problem that I'm having is when I disconnect the temp sending plug, the motor barely runs and has trouble starting. I've attempted to put that unit in a glass of water and start it, but that doesn't solve it.

    My 2 questions are: 1. Would shorting the two lead wires together 'trick' the computer that the unit is still working? 2. Is there a different place that I can go into the block to get my temperature?

    It doesn't have to be a pro fix, I picked this limo up for $1,000. Runs well, but can not see the temperature, and when I'm hauling a bunch of friends around in it I'd like to know whats going on.

    Unit is here: http://cityhicks.com/limo/S5031750-1.JPG

    Thanks!

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  3. #2
    Gwokable is offline Cadillac Owners Fanatic
    Automobile(s): 1988 Cadillac Fleetwood Brougham
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    Re: Temp Sending unit mystery

    Something I know about the 307 intake manifold (which shouldn't be much different than a 350) is that it has several spots for coolant temperature sensors. Depending on the engine, you may have a Temp sensor, sensor for the EVAP system, and an EFE sensor. One of the changes over the years to the 307 is that they installed an electronic EVAP system into the car which bypasses the need for the EVAP Thermal Vacuum Switch, although some of the engines still have the TVS. You can basically pull that, get a good ol' temperature sensor, thread it in and in 5 minutes you're done. Check around the blocks intake manifold, look for plugs; some are for air, others are for coolant and it's easy to tell since one you remove one, you'll get coolant flowing out of it.

    As far as connecting the leads, it depends on the draw but you shouldn't have an issue so long as you connect them in parallel.

  4. #3
    bigbluebrougham's Avatar
    bigbluebrougham is offline Cadillac Owners Fanatic
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    Re: Temp Sending unit mystery

    You might have a couple of plugs in the heads too. I had a 93 chevy pickup with that exact same motor and ran the temp sensor into one of the plugs in the head. Worked great and it was really accurate since it was at the hottest part of the motor. I would check that out.

    BBB

  5. #4
    90Brougham350's Avatar
    90Brougham350 is offline Cadillac Owners Connoisseur
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    Re: Temp Sending unit mystery

    Driver-side head, under the #3 cylinder is a plug. This is the spot you want. There's already a temperature sensor in there, but it's wired to the idiot light, not the ECM. Don't touch the one on top of the manifold, the one you're trying to work with. This is the CTS, the coolant temperature sensor. It's one of the 4 sensors the computer uses to set the spark timing. Without it plugged in the engine will run like crap because it will fall back on pre-programmed timing tables. Use the spot in the head for your sensor. It won't affect anything. The sensor on the waterneck is plugged into the ECM, and, as you know, screws up the engine when you unplug it.

  6. #5
    bigbluebrougham's Avatar
    bigbluebrougham is offline Cadillac Owners Fanatic
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    Re: Temp Sending unit mystery

    Thanks 90Brougham350. I couldn't remember where that plug was since I got rid of the pickup.

    BBB

  7. #6
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
    Automobile(s): 94 Fleetwood Brougham
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    Re: Temp Sending unit mystery

    90Brougham is correct, that is not the temp SENDING UNIT, that is the CTS, or Coolant Temp Sensor, it won't run well at all ever without it. It sees it open and thinks it is super cold and dumps fuel like crazy. Don't mess with this sensor or its location, it needs to be here. Well, I would like to see it in the heads myself, I feel that is a more accurate location for what it needs to do.

    Look for plugs in the heads and in the intake water crossover, those are where it needs to go, do not mess with the CTS.

    Check the Z28 forums, see where they put the factory sensors, most likely there is nothing more than a plug in the hold in your engine, as the LG4 is very similar to the L05 and was installed in Z28's as the base engine. But the heads are likely the right place. Pontiac started that in the 70's.

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