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Dash Temp Guage-Coolant Temp Switch

This is a discussion on Dash Temp Guage-Coolant Temp Switch within the Technical / Maintenance forums, part of the General Discussion category; Ok since I bought my new (to me) truck the temperature gauge on the dash has not worked. Simple fix, ...

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    Registered User mercury89's Avatar
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    Dash Temp Guage-Coolant Temp Switch


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    Ok since I bought my new (to me) truck the temperature gauge on the dash has not worked. Simple fix, I thought anyway, but now I cant seem to solve the problem.

    Truck is a 1995 K1500 Z71, 5.7, auto, RCSB, stock except for NBS wheels.

    Now to test to test the gauge circuit, I grounded out the plug end to the engine block and the gauge pegged. So the gauge must be working.
    I then replaced the Engine Coolant Temperature Switch--the one on the side of the block on the driver side between the spark plugs. Still doesnt work.
    Then I went ahead and replaced the Coolant Temp Sensor--the one by the thermostat housing. That didnt fix it either.

    Im getting to my wits end trying to figure this out, I just want to make the gauge on the dash work

    If anyone has any ideas or thoughts of what I could be doing wrong, something I overlooked or any random thoughts at all please share and hopefully I can figure this out! :fsc:
    1994 K1500 Z71,ECSB, 4" Trailmaster Lift, 33" BFGs,4.10s, Flowmaster 50 Sold 7/15/2008
    1995 K1500 Z71, RCSB, 5.7, Stock, 65000 miles

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    Registered User 01BlackBeauty's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    you need to replace the coolant temperature SENSOR again, i had to put one in my 93' from autozone and the first one i got was faulty, the second worked like a charm
    Last edited by 01BlackBeauty; 06-01-2009 at 09:35 PM.

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    Re: Dash Temp Guage-Coolant Temp Switch

    Is it a real guage ? The temp guage on my Z/28 stays at 210 all the time unless it is warming up or it overheats. It is more likean idiot light, not a "real" guage.
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    Registered User mercury89's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    Update: gauge moves slightly. When fully cold it starts at 100 (lowest value) and moves about one small mark up. Thats it. I know that the temp on the block is 180-190 because I previously checked that with an IR thermometer but I would like the gauge to work so I can monitor engine temp in the mountains.


    Quote Originally Posted by 01BlackBeauty View Post
    you need to replace the coolant temperature SENSOR again, i had to put one in my 93' from autozone and the first one i got was faulty, the second worked like a charm
    Is the sensor the one by the thermostat housing or the one on the block between the spark plugs?

    Quote Originally Posted by Danger713 View Post
    Is it a real guage ? The temp guage on my Z/28 stays at 210 all the time unless it is warming up or it overheats. It is more likean idiot light, not a "real" guage.
    Not exactly sure what you mean but it seems to be a real gauge, its not just a light. The gauge starts at 100 (lowest value) and moves a 1/4" inch.
    1994 K1500 Z71,ECSB, 4" Trailmaster Lift, 33" BFGs,4.10s, Flowmaster 50 Sold 7/15/2008
    1995 K1500 Z71, RCSB, 5.7, Stock, 65000 miles

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    Re: Dash Temp Guage-Coolant Temp Switch

    The sensor buy the t-stat should be for the computer.
    When you put them in did you put thread tape on them? If so take them out take the thread tape off and put them back in. That keeps them from grounding to the block/head.

    Like was said ealier could just be a bad sensor.


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    Registered User 01BlackBeauty's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    the one by the thermostat housing is called the coolant temperature switch which as stated is for the computer to control such things as fuel mixture and shift points, the one on the block between the plugs is the coolant temperature Sensor, which controls the guage as it's only function

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    Re: Dash Temp Guage-Coolant Temp Switch

    I have same EXACT issue...been chasing it for a while. Just put in a new temp switch in head, which goes to gauge, no difference.

    I HATE WASTING MONEY chasing things like this down. If I spend money and fix it, it does not bother me but this is total BS. If I read that one thread enuff times, I may try using a resistor.
    1993 Chevy 5.7 tbi Z71, vortec heads, GMPP tbi vortec intake, 2" TBI and bored intake, TBI spacer, Comp Cams 08-409-8 XTREME 4x4 roller cam conversion, Hedman full length headers, 3" body lift, 33" tires, Paxton Performance tune (aka 94Blazer383), 4.10's, Hypertech powercharger, built 4l60e.

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    GMC RULZZ NEUMANNZZ's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    did you check the sensor with a multimeter set to ohms? check hot and cold readings report back.
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    Registered User mercury89's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    First off, thanks for all the ideas and help guys!

    Quote Originally Posted by 01BlackBeauty View Post
    the one by the thermostat housing is called the coolant temperature switch which as stated is for the computer to control such things as fuel mixture and shift points, the one on the block between the plugs is the coolant temperature Sensor, which controls the guage as it's only function
    I thought it was the other way around--Temp switch is on the block (for the gauge), and temp sensor is by the T-stat and is for the computer

    Quote Originally Posted by 93ChevyTBI View Post
    I have same EXACT issue...been chasing it for a while. Just put in a new temp switch in head, which goes to gauge, no difference.

    I HATE WASTING MONEY chasing things like this down. If I spend money and fix it, it does not bother me but this is total BS. If I read that one thread enuff times, I may try using a resistor.
    Yeah, very annoying and it seems like you isolated the problem only to find out that the problem lies somewhere else.

    Quote Originally Posted by kcb37 View Post
    The sensor buy the t-stat should be for the computer.
    When you put them in did you put thread tape on them? If so take them out take the thread tape off and put them back in. That keeps them from grounding to the block/head.

    Like was said ealier could just be a bad sensor.
    No thread tape. Just screwed it into the block.

    Quote Originally Posted by NEUMANNZZ View Post
    did you check the sensor with a multimeter set to ohms? check hot and cold readings report back.
    I need to do this, I just need to buy/borrow/steal a multimeter. Hopefully I can do this today!
    1994 K1500 Z71,ECSB, 4" Trailmaster Lift, 33" BFGs,4.10s, Flowmaster 50 Sold 7/15/2008
    1995 K1500 Z71, RCSB, 5.7, Stock, 65000 miles

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    Registered User mercury89's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    I finally got around to measuring the resistance values in the sensor. Full hot, the resistance in the sensor is ~300 ohms. I looked the value up in a table and it seems to correspond to about 180 degrees F. This seems to be pretty normal?

    I need to check the cold reading in the morning.

    Also I received an SES light while driving on the freeway today, a code 15 and a code 32. The 15 is coolant sensor (low temp) so I guess it thinks that the temp is too low which is reflected in the gauge barely moving? If anyone has any ideas where to start looking for the issue that is causing this code please feel free to throw some ideas out there.

    The code 32 is an EGR code, Ill look into that separately.

    Thanks guys.
    1994 K1500 Z71,ECSB, 4" Trailmaster Lift, 33" BFGs,4.10s, Flowmaster 50 Sold 7/15/2008
    1995 K1500 Z71, RCSB, 5.7, Stock, 65000 miles

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    Re: Dash Temp Guage-Coolant Temp Switch

    Quote Originally Posted by mercury89 View Post
    I finally got around to measuring the resistance values in the sensor. Full hot, the resistance in the sensor is ~300 ohms. I looked the value up in a table and it seems to correspond to about 180 degrees F. This seems to be pretty normal?

    I need to check the cold reading in the morning.

    Also I received an SES light while driving on the freeway today, a code 15 and a code 32. The 15 is coolant sensor (low temp) so I guess it thinks that the temp is too low which is reflected in the gauge barely moving? If anyone has any ideas where to start looking for the issue that is causing this code please feel free to throw some ideas out there.

    The code 32 is an EGR code, Ill look into that separately.

    Thanks guys.

    The code 15 has to do with the CTS switch at the thermostat housing, not the gauge switch in the head....2 separate switches there. The one in the head is only for the gauge....it doesn't tell the computer anything and won't set any codes.
    1993 Chevy 5.7 tbi Z71, vortec heads, GMPP tbi vortec intake, 2" TBI and bored intake, TBI spacer, Comp Cams 08-409-8 XTREME 4x4 roller cam conversion, Hedman full length headers, 3" body lift, 33" tires, Paxton Performance tune (aka 94Blazer383), 4.10's, Hypertech powercharger, built 4l60e.

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    Registered User bwood's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    Quote Originally Posted by 01BlackBeauty View Post
    the one by the thermostat housing is called the coolant temperature switch which as stated is for the computer to control such things as fuel mixture and shift points, the one on the block between the plugs is the coolant temperature Sensor, which controls the guage as it's only function
    Actually they are both sensors. They are different types. A switch would be a device that opens or closes, like what is found on older vehicles with only a warning light. The CTS is located at the thermostat housing and is used to tell the ECM the temp of the coolant at the intake. I uses this info to control wheather the engine is in open or closed loop mode and also adjusts the fuel and spark curves. The coolant temp guage sensor is a one wire sensor that changes resistance between the brass housing and the wire thus effecting the ground resistance between the guage and engine block ground. Just as a test take a piece of bare copper wire and wrap one end around the brass sensor and the other at a good ground on the engine, see if the guage starts to work. It is common to have so much teflon tape on the threads that it breaks the ground between the sensor and block. Use a thread sealing paste like teflon paste instead. I used black rtv on mine, but you have to let the rtv cure some before introducing it to any liquids.

    Edit: Also, I would advise against buying electronic components from Autozone (Wells). I have had good luck with Borg Warner from Oreilly, but you can't go wrong with OEM stuff. It can be purchased from most parts houses, you just have to ask as they are going to push their house brand.
    Last edited by bwood; 06-05-2009 at 07:50 AM.
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    Re: Dash Temp Guage-Coolant Temp Switch

    Quote Originally Posted by bwood View Post
    Edit: Also, I would advise against buying electronic components from Autozone (Wells). I have had good luck with Borg Warner from Oreilly, but you can't go wrong with OEM stuff. It can be purchased from most parts houses, you just have to ask as they are going to push their house brand.
    you really thin it's the Autozone part? Throw out a % for me.....25% it could be the Autozone part or more like 80%? I hate to replace a sensor that has a only 2 miles on it.
    1993 Chevy 5.7 tbi Z71, vortec heads, GMPP tbi vortec intake, 2" TBI and bored intake, TBI spacer, Comp Cams 08-409-8 XTREME 4x4 roller cam conversion, Hedman full length headers, 3" body lift, 33" tires, Paxton Performance tune (aka 94Blazer383), 4.10's, Hypertech powercharger, built 4l60e.

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    Re: Dash Temp Guage-Coolant Temp Switch

    I have the same temp gauge problem with my 92 Chevy. I agree on cheap Auto Zone and Advance Auto part. It is better to buy the know brand name or OEM part.

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    Registered User mercury89's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    Update: full cold on both sensors, resistance is ~2500 ohms. Seems about right, its about 70 degrees out this morning.

    Quote Originally Posted by 93ChevyTBI View Post
    The code 15 has to do with the CTS switch at the thermostat housing, not the gauge switch in the head....2 separate switches there. The one in the head is only for the gauge....it doesn't tell the computer anything and won't set any codes.
    ok thank you. I recently replaced (week ago) the sensor at the thermostat housing with a unit from NAPA auto parts. So either I got a faulty part or theres a wiring issue. Im starting to think it must be wiring because the gauge moves, just very very little. It starts off where its supposed to be (100) and then moves maybe 1/8"-1/4" depending on where Im driving to.

    Quote Originally Posted by bwood View Post
    Just as a test take a piece of bare copper wire and wrap one end around the brass sensor and the other at a good ground on the engine, see if the guage starts to work. It is common to have so much teflon tape on the threads that it breaks the ground between the sensor and block. Use a thread sealing paste like teflon paste instead. I used black rtv on mine, but you have to let the rtv cure some before introducing it to any liquids.

    Edit: Also, I would advise against buying electronic components from Autozone (Wells). I have had good luck with Borg Warner from Oreilly, but you can't go wrong with OEM stuff. It can be purchased from most parts houses, you just have to ask as they are going to push their house brand.
    I grounded out the gauge circuit to the block to make sure the gauge wasnt mechanically damaged and it pegged it. I used no teflon tape on either sensor, they were both threaded into the block bare. I need to try grounding out the sensor to the block with it hooked up so I can see if grounding is an issue.
    1994 K1500 Z71,ECSB, 4" Trailmaster Lift, 33" BFGs,4.10s, Flowmaster 50 Sold 7/15/2008
    1995 K1500 Z71, RCSB, 5.7, Stock, 65000 miles

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    Re: Dash Temp Guage-Coolant Temp Switch

    Years ago Napa sold super quality products made in USA, now their products are the same as AutoZone and Advance Auto with just a higher price.

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    Re: Dash Temp Guage-Coolant Temp Switch

    I hate to say it bud , but it not the new sensor and it's probably not the old sensor, it's the gauge. I have a 99 tahoe OBS and have the same problem. It's a common problem on old body style trucks. My sensor reads exactly what it should at 195Deg ~241 ohms but my gauge only goes up to 160 tops. Ground the wire and it pegs the gauge , so that test only works if the gauge is completely dead. Bad news is you cant replace the gauge, you have to replace the entire cluster. Only other thing I can think of is to check the resistance of the wire from the sensor to the gauge. If the wire has some resistance (it shoudln't) that would caude the problem. Don't feel like going that far on mine.

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    Registered User mercury89's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    Quote Originally Posted by TAA-HOE View Post
    I hate to say it bud , but it not the new sensor and it's probably not the old sensor, it's the gauge. I have a 99 tahoe OBS and have the same problem. It's a common problem on old body style trucks. My sensor reads exactly what it should at 195Deg ~241 ohms but my gauge only goes up to 160 tops. Ground the wire and it pegs the gauge , so that test only works if the gauge is completely dead. Bad news is you cant replace the gauge, you have to replace the entire cluster. Only other thing I can think of is to check the resistance of the wire from the sensor to the gauge. If the wire has some resistance (it shoudln't) that would caude the problem. Don't feel like going that far on mine.
    Well darn it, I guess I'll look into it a little bit more but if this really is a common problem I dont think Im going to bother with a full cluster swap to get my temp gauge working. Just a quick question for you: do you get any SES light codes from your temp gauge not working correctly?

    If I cant get the dash gauge working, I will probably just install a small, unobtrusive aftermarket eletric temp gauge somewhere. Hopefully they are not too difficult to install.
    1994 K1500 Z71,ECSB, 4" Trailmaster Lift, 33" BFGs,4.10s, Flowmaster 50 Sold 7/15/2008
    1995 K1500 Z71, RCSB, 5.7, Stock, 65000 miles

  19. #19
    Chevy truck owner The_Ogre25's Avatar
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    Re: Dash Temp Guage-Coolant Temp Switch

    You will not get a code from the sensor int the head. Your low temp code is something different, triggered by the sensor in the t-stat housing. I would verify the actual coolant temp with a cheap aftermarket gauge first. Also when you put the gauge back in did you refill and bleed the system again? You might have a air bubble right there.

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    Re: Dash Temp Guage-Coolant Temp Switch

    I've been thinking of taking a short-cut on fixing this. Let me know if it will work or not. I've had my cluster out 2-3 times and it's pretty easy. Can I use an infra-red gun or laptop/scanner to see what my temp really is and just pull the needle off the gauge and put it back where it needs to be?

    Please let me know before I try this. Thanx
    1993 Chevy 5.7 tbi Z71, vortec heads, GMPP tbi vortec intake, 2" TBI and bored intake, TBI spacer, Comp Cams 08-409-8 XTREME 4x4 roller cam conversion, Hedman full length headers, 3" body lift, 33" tires, Paxton Performance tune (aka 94Blazer383), 4.10's, Hypertech powercharger, built 4l60e.

 

 
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