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Old 11-05-2011, 03:21 AM   #1
PlasticCarsRock
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Default Resistance vs Temperature chart for gen1 gauge temperature sender?

Does anyone have the values necessary to test the gauge temperature sender in a gen1 S-Series? (The second, different, ECTS that controls only the gauge.)

I've been having some trouble with the temperature gauge on my '95 SL2. Until recently, it had an OE replacement sensor installed in 2000 or 2001 (at a Saturn dealer). However, the plastic connector end on that sensor was cracked at some point while the engine was out, this past summer, and since then, the gauge reading was a bit sporadic: it stayed in the same general area, but instead of sitting still at a hair below 1/2, as it always had, it would wander up and down from time to time, even at highway speed (not near the fan turn on point, but more than normal). Figuring it was either the sensor or one year old Stant 195 thermostat, I decided to replace the sensor first, as I knew that it was damaged. I got a lifetime warranty sensor from Advance Auto (BWD was the brand).

With the new sensor, the gauge no longer moved when it shouldn't, however, it reads a bit lower on the gauge than I'm used to: instead of reading just a hair below 1/2, as it should and always has, it now reads at 3/8 on the gauge (this is a '95 so it should be just below 1/2, NOT 3/8 like the newer models).

Hoping it was a defective sensor, I took advantage of the warranty and replaced it with another. I also replaced the Stant thermostat with another, just in case. It still reads exactly the same.

I have tested the coolant temperature in the overflow tank, and read values straight from the main ECTS, both suggesting that the engine is running at the correct temperature. But this was with the car sitting still, so I suppose it's possible that it rose slightly above the normal temperature.

The fan turns on earlier on the gauge than it used to, indicating that the gauge is reading lower, as suspected.

Is it possible that the gauge temperature senders were revised to provide the same gauge operation of the newer models (despite them not using the separate sensor)?

Is this brand (BWD) just a bit off in general?

I can live with the different gauge operation, but I would like to confirm that the temperature sender is different, not the engine temperature.
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Old 11-05-2011, 10:13 PM   #2
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Default Re: Resistance vs Temperature chart for gen1 gauge temperature sender?

Resistance to temp chart (OldNuc link) http://www.saturnfans.com/photos/sho...hp?photo=50531

Quote:
Originally Posted by Luke View Post
Guage Reading:

1/4 mark = 180 F
1/2 mark = 208 F
3/4 mark = 232 F
HOT.......= 270 F

Source: Factory Service Manual, 1995 SL2
page 37 elip. (Instrument Panel Cluster)
...
1996 SL2, 5-speed, 155,638 miles (149,600 when purchased), Nationwide Emission
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Old 11-05-2011, 10:40 PM   #3
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Default Re: Resistance vs Temperature chart for gen1 gauge temperature sender?

Same values as the ECTS. Just convert the temperature to resistance. The temp/resistance chart is in my gallery. Use the middle of a given resistance range for each temperature. The gauge sensor has both pins connected to 1 end of the thermistor and the other end is connected to the shell. Connect test resistor from the connector to block to check the gauge.

Saturn 96 model year and newer temperature gauge reading vs. actual temperature as read from the ECTS.

GAGE Reading..........ECTS Temperature..........Event
.....1/4.................................150 F
.....3/8.................................192 F...................T-stat cracks open
.....3/8+................................195 F
.....1/2.................................212 F
.....9/16................................221 F...................Fan ON
.....7/16................................210 F...................Fan OFF coast to 205 F

The installed thermostat is marked as 87 C

Add 1/8 to the gauge reading column to obtain the corresponding gauge indication for Saturn 95 model year and older.

Quote:
Originally Posted by PlasticCarsRock View Post
Does anyone have the values necessary to test the gauge temperature sender in a gen1 S-Series? (The second, different, ECTS that controls only the gauge.)

I've been having some trouble with the temperature gauge on my '95 SL2. Until recently, it had an OE replacement sensor installed in 2000 or 2001 (at a Saturn dealer). However, the plastic connector end on that sensor was cracked at some point while the engine was out, this past summer, and since then, the gauge reading was a bit sporadic: it stayed in the same general area, but instead of sitting still at a hair below 1/2, as it always had, it would wander up and down from time to time, even at highway speed (not near the fan turn on point, but more than normal). Figuring it was either the sensor or one year old Stant 195 thermostat, I decided to replace the sensor first, as I knew that it was damaged. I got a lifetime warranty sensor from Advance Auto (BWD was the brand).

With the new sensor, the gauge no longer moved when it shouldn't, however, it reads a bit lower on the gauge than I'm used to: instead of reading just a hair below 1/2, as it should and always has, it now reads at 3/8 on the gauge (this is a '95 so it should be just below 1/2, NOT 3/8 like the newer models).

Hoping it was a defective sensor, I took advantage of the warranty and replaced it with another. I also replaced the Stant thermostat with another, just in case. It still reads exactly the same.

I have tested the coolant temperature in the overflow tank, and read values straight from the main ECTS, both suggesting that the engine is running at the correct temperature. But this was with the car sitting still, so I suppose it's possible that it rose slightly above the normal temperature.

The fan turns on earlier on the gauge than it used to, indicating that the gauge is reading lower, as suspected.

Is it possible that the gauge temperature senders were revised to provide the same gauge operation of the newer models (despite them not using the separate sensor)?

Is this brand (BWD) just a bit off in general?

I can live with the different gauge operation, but I would like to confirm that the temperature sender is different, not the engine temperature.
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Old 11-06-2011, 01:09 AM   #4
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Default Re: Resistance vs Temperature chart for gen1 gauge temperature sender?

Quote:
Originally Posted by OldNuc View Post
Same values as the ECTS.
Alright, that's what I needed to know. I'll check it tomorrow.

I'm pretty sure the sensor is the issue though. Any ideas why it would be different than OE?
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Old 11-06-2011, 09:04 AM   #5
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Default Re: Resistance vs Temperature chart for gen1 gauge temperature sender?

One of the more popular failure modes for the thermistor is to shift its temp/resistance curve and slightly modify the shape. Gives the illusion that it is working just fine but provides bad data. Complete open or short circuit is not a common failure. It is age/environment related but not that predictable. The short side recommended qualified life is 5 years and the nominal is 10 years. Keep in mind that is environmentally qualified life and not the general use service life. You can usually double the environmental qualified life and have a good estimate of the service life. In this case that would be 10->20 years. That does not mean no failure before 5 or 10 years either. There are always some random failures.
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Old 11-06-2011, 02:07 PM   #6
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Default Re: Resistance vs Temperature chart for gen1 gauge temperature sender?

Quote:
Originally Posted by OldNuc View Post
One of the more popular failure modes for the thermistor is to shift its temp/resistance curve and slightly modify the shape. Gives the illusion that it is working just fine but provides bad data. Complete open or short circuit is not a common failure. It is age/environment related but not that predictable. The short side recommended qualified life is 5 years and the nominal is 10 years. Keep in mind that is environmentally qualified life and not the general use service life. You can usually double the environmental qualified life and have a good estimate of the service life. In this case that would be 10->20 years. That does not mean no failure before 5 or 10 years either. There are always some random failures.
But two new one failed in exactly the same way, before I even got them? I know auto parts stores are notorious for questionable or downright pathetic parts, but that seems like a bit of a stretch.
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Old 11-06-2011, 03:06 PM   #7
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Default Re: Resistance vs Temperature chart for gen1 gauge temperature sender?

Be very sure the ID-10-T behind the counter actually sold you the correct part. The connectors will fit on the incorrect part. The gauge sensor has a grounded thermistor and the 2 contact pins are common to each other and isolated from the shell. The ECTS and IAT have the thermistor connected between the 2 contact pins.
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Old 11-06-2011, 06:20 PM   #8
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Default Re: Resistance vs Temperature chart for gen1 gauge temperature sender?

Quote:
Originally Posted by OldNuc View Post
Be very sure the ID-10-T behind the counter actually sold you the correct part. The connectors will fit on the incorrect part. The gauge sensor has a grounded thermistor and the 2 contact pins are common to each other and isolated from the shell. The ECTS and IAT have the thermistor connected between the 2 contact pins.
What incorrect part? Unless I'm very mistaken, the plug will not fit on a regular ECTS (the are slightly different, inside). Is there some other sensor that will fit?
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Old 11-06-2011, 06:52 PM   #9
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Default Re: Resistance vs Temperature chart for gen1 gauge temperature sender?

The majority of aftermarket sensors will swap, it has been done. Check, it's easy. If you read zero between the pins it is the correct configuration.
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Old 11-06-2011, 06:53 PM   #10
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Default Re: Resistance vs Temperature chart for gen1 gauge temperature sender?

If it is the wrong configuration the gauge will not read at all.
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