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EA82 CTS / Coolant Temperature Sensor readings


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This is my collection of measurements of the CTS.


temp   sensor ohms
14F     7000 - 11500
68F     2000-3000
122F   700-1000

Above are from the FSM.

Below are actual measurements. Done at 2 different times, compiled here. The 1990 unit was in a good running engine. The new dealer unit was bought locally, and I made the measurements before installing it to get the extra reference points.
                   measured ohms
temp  1990 used      new dealer unit
77F           -                     2390
122F      1154                 1098
185F         -                      400
190F       454                     -

More measurements from some runs in 2020 -

Temps measured with a Fluke62 max+ IR thermometer.
Voltages while running, connected to the ECU with a Fluke 77 Multimeter.
Ohms after / before, while off, connected to ECU, same meter.
temp    ohms      volts
79F      1108     2.73V
 -          1130     2.79V
77F      1139     2.81V

193F     259      .680V
  -          262      .714V
  -          268      .735V
192F     242      .652V

 

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That is a standard Bosch/GM NTC (thermistor) resistance value. You can use any $20 GM sensor in it's place. For example:

https://www.amazon.com/ACDelco-213-77-Original-Equipment-Temperature/dp/B000C9JS5C

Or a Bosch unit (metric):

https://www.bosch-motorsport.com/content/downloads/Raceparts/en-GB/53687307119081483.html#/Tabs=53698955/

Bosch also lists the values along with it. REALLY common stuff when you are doing standalone EFI setups and tuning. These are used everywhere - coolant temp, manifold temp, intake air temp, etc. They have brass, plastic, open element.... anything you could want and they are CHEAP. 

Bosch essentially set all these standards back in the 70's, GM adopted them along with a lot of Bosch components and rolled them into their Rochester Fuel Systems products and a couple billion GM products were built with Rochester (Bosch) injectors, temp sensors, and other bits. Subaru just copied GM because that's what they could buy cheap and it was essentially industry standard (and in many cases still is). 

GD

Edited by GeneralDisorder
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19 hours ago, GeneralDisorder said:

That is a standard Bosch/GM NTC (thermistor) resistance value. You can use any $20 GM sensor in it's place. For example:

https://www.amazon.com/ACDelco-213-77-Original-Equipment-Temperature/dp/B000C9JS5C

Or a Bosch unit (metric):

https://www.bosch-motorsport.com/content/downloads/Raceparts/en-GB/53687307119081483.html#/Tabs=53698955/

Bosch also lists the values along with it. REALLY common stuff when you are doing standalone EFI setups and tuning. These are used everywhere - coolant temp, manifold temp, intake air temp, etc. They have brass, plastic, open element.... anything you could want and they are CHEAP. 

Bosch essentially set all these standards back in the 70's, GM adopted them along with a lot of Bosch components and rolled them into their Rochester Fuel Systems products and a couple billion GM products were built with Rochester (Bosch) injectors, temp sensors, and other bits. Subaru just copied GM because that's what they could buy cheap and it was essentially industry standard (and in many cases still is). 

GD

Just to add they are plain jane 2.2K thermistors in side. If you look up a chart for one they match right up with the values for sensor.

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