Engine Metal Temperature Switch
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HT4100 4.1, 4.5, 4.9 Discussion, Engine Metal Temperature Switch in Cadillac Engine Technical Discussion; My 1988 Sedan Deville lights up the "Stop Engine Temp" light after 20 or 30 minutes driving. I have monitored ...
  1. #1
    donpato is offline Cadillac Owners Member
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    Question Engine Metal Temperature Switch

    My 1988 Sedan Deville lights up the "Stop Engine Temp" light after 20 or 30 minutes driving. I have monitored the coolant temperature and that "Stop Engine Temp" light comes on when the coolant temperature reaches about 105 degrees Celsius.

    I understand that that "Stop Engine Temp" light should light up when the back of the driver's side head gets to 380 degrees Farenheit (160 Celcius) as sensed by the "engine metal temperature switch". So this "Stop Engine Temp" is not activated by the coolant temperature but rather the engine metal temperature as sensed by the aforementioned "engine metal temperature switch".

    It strikes me as pretty odd that I get a "Stop Engine Temp" light when the coolant temperature is only around 105 Celcius. Is it possible that the Metal Temperature can be so much higher than the coolant temperature?

    I have been totally unable to find a replacement "engine metal temperature switch" for this 1988 Sedan Deville.

    As usual any help will be very much appreciated

    Regards

    Patricio

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  3. #2
    ThomasO's Avatar
    ThomasO is offline Cadillac Owners Fanatic
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    Re: Engine Metal Temperature Switch

    See if you can find the switch here:
    http://www.partsamerica.com/SearchResults.asp
    ....................... OR HERE.............................
    http://www.1aaia.com/cadillac_auto_part.html

  4. #3
    kcnewell is offline Cadillac Owners Connoisseur
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    Re: Engine Metal Temperature Switch

    Quote Originally Posted by donpato
    My 1988 Sedan Deville lights up the "Stop Engine Temp" light after 20 or 30 minutes driving. I have monitored the coolant temperature and that "Stop Engine Temp" light comes on when the coolant temperature reaches about 105 degrees Celsius.

    I understand that that "Stop Engine Temp" light should light up when the back of the driver's side head gets to 380 degrees Farenheit (160 Celcius) as sensed by the "engine metal temperature switch". So this "Stop Engine Temp" is not activated by the coolant temperature but rather the engine metal temperature as sensed by the aforementioned "engine metal temperature switch".

    It strikes me as pretty odd that I get a "Stop Engine Temp" light when the coolant temperature is only around 105 Celcius. Is it possible that the Metal Temperature can be so much higher than the coolant temperature?

    I have been totally unable to find a replacement "engine metal temperature switch" for this 1988 Sedan Deville.

    As usual any help will be very much appreciated

    Regards

    Patricio
    Are you monitoring the engine coolant temp by looking at the engine coolant temp in the ECM data parameters in the onboard diagnostics or thru some external means?

    I agree with your conclusions if you are looking at the coolant temp thru the ECM data parameters as that would indicate that the coolant temp is normal and that the metal temp switch is turning on the warning. If, however, you are monitoring coolant temp thru some other means then the coolant temp sender could be at fault causing the light.

    Have you checked at a Cadillac dealer for the metal temp switch. I don't know that an aftermarket switch is available for replacement. On an 88, to check the coolant temp per the ECM data parameters use the following sequence. Enter the onboard diagnostics by simultaneously pressing and holding the OFF and WARMER buttons with the key on/engine running until the onboard diagnostics activates. After any trouble codes display the system will prompt you with .7.0 This means system ready. Press the LO button on the climate control panel to go to the ECM data parameters section. The display should show E.9.0 Scroll thru the ECM data parameters section using the HI/LO section to find the parameter P.0.4 That is the coolant temperature from the coolant temp sensor that the ECM is using and that is used to activate the overheat warning. If that sensor is reading 105C when the warning is lit then I would agree that the issue is the metal temp switch being failed. A dealer should have a replacement.

  5. #4
    donpato is offline Cadillac Owners Member
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    Re: Engine Metal Temperature Switch

    Thanks so much for your replies, yes I am checking the coolant temp per the ECM data parameters.

    There are no Cadillac Dealers here in Chile, I brought the casr back from the states after working there for 6 years.

    I have ben unable to find a site to buy the "engine metal temperature switch", tried carparts.com, as well as thos two mentioned by you.

    Best Regards

    Patricio

  6. #5
    kcnewell is offline Cadillac Owners Connoisseur
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    Re: Engine Metal Temperature Switch

    Cadillac needs to get to Chile. That is a problem for parts. Just out of curiosity, are you positive that the cooling system is full of coolant? Check the radiator itself when the system is cold. Don't trust the level in the coolant recovery bottle. If the rad cap is not working correctly or is the wrong cap the coolant recovery bottle can by full and the radiator/cooling system could be very low. If the cooling system is very low the coolant sensor could be left "dry" in the intake manifold and show normal temperature of 105C while the engine could be overheating severely and turning the metal temp lite on. In other words are you positive that the engine is not overheating - the engine metal temp switch may be working as it is designed to and warning you of a hot engine but the coolant temp sensor is not reading this due to low coolant. The coolant temp sensor is screwed into the intake manifold on the top of the engine so if the coolant level gets low the coolant temp sensor will not "see" the coolant and will read the metal temp of the manifold and/or the steam around it. It will read much lower than the metal temp of the head.

    What is odd about the situation that makes me suggest the above scenario is that the metal temp switches are pretty simple, robust devices... I don't remember one ever failing personally but that was a long time ago and that switch in your car is 16 years old. But, when they would fail, the failure mode is either open or shorted not a shift in the temperature setting as the situation you describe suggests.

  7. #6
    donpato is offline Cadillac Owners Member
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    Re: Engine Metal Temperature Switch

    Thanks kcnewell, yes I have checked the radiator and it seems to be full of coolant. But as you say there is still the posibility that the engine metal switch is working ok and of course I would hate to destroy my engine. Right now I guess the easiest thing to do is change the switch to see if the light still comes on when the coolant temperature is slightly above 105 degrees celcius.

    Regards

    Patricio

  8. #7
    donpato is offline Cadillac Owners Member
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    Re: Engine Metal Temperature Switch

    By the way, which is supposed to be a reasonable range for the coolant temperature fr these cars?


    As mentioned in an earlier mail my coolant temperature reaches 100 degrees celcius where it starts the cooling fans and then more or less fluctuates between 95 and 105 degrees celcius.

    Regards

    Patricio

  9. #8
    kcnewell is offline Cadillac Owners Connoisseur
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    Re: Engine Metal Temperature Switch

    Quote Originally Posted by donpato
    By the way, which is supposed to be a reasonable range for the coolant temperature fr these cars?


    As mentioned in an earlier mail my coolant temperature reaches 100 degrees celcius where it starts the cooling fans and then more or less fluctuates between 95 and 105 degrees celcius.

    Regards

    Patricio
    That's a perfectly normal temp range. The system will probably go up to even 110-115C under load and will function fine even at 120-125C on excursions in very hot weather/high load. It should not boil until 128C with 50/50 coolant/distilled water and a 15 PSI/1 bar pressure cap.

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