I have an 85 gsl with a 4 port 13b, the sensor is located in rear iron above ops. I have tested the sensor, guage, and repaired old brittle wiring.
the guage still barely registers. Any advice or experience? I have the dash apart repairing high beams, should I fiddle with the guage?

 

Did you follow this thread for testing? https://www.rx7club.com/1st-generati...gauge-1074146/. If the gauge tested good, it has to be the sensor.

Because water temp is critical to a rotary, I always suggest adding an after market gauge in addition to the factory one.

 

Mine would barely leave the cold line because my thermostat was stuck open. Does your heat blow hot?

 

T-Stat is newish, there are two different senders one has a tapered thread, and the other is straight with a sealing washer. It's an old 70s block, I have a taper fit sender , perhaps I need the other type? Guage has never worked correctly since I bought the car. I have checked the cooling syst and am assured it is working correctly, and at correct op temp..

 

Two sensors on the left side rear iron.
Top is oil pressure sensor, bottom is coolant temp sensor.

I have an 84 12a, but the sensors are universal for 12a/13b for our years.

I'm not promoting Atkins, just needed images and application info.

 

Have you considered that there maybe a partial blockage in the coolant passage where the sender probe sticks into the passage?

If you have a new sender and you are sure the gauge is good, the only issue I would consider is the wiring or a blockage in the coolant passage.

 

I think it's the incorrect sender, I need the washer type without the taper threads. Seems to be what is advised for older motors.

 

I personally prefer mechanical temp gauges to electronic ones. If you can't figure it out the. Just get an after market mechanical one. No electronics to fiddle with.

 

How the sending unit attaches to your engine is irrelevant if the sensors use the same baseline voltage - which these seem to have.

I'm with the other guys that if you can't get your heater to blow hot - then you have a cold engine condition; thermostat stuck open or clogged heater core, if the engine otherwise seems to come to temperature.

If the heater blows hot air, and your gauge still shows cold - it could be a bad sending unit, or a blockage in that part of the coolant path which is preventing coolant to flow past the sensor, again, if the engine otherwise seems to come up to temp.

If replacing the sending unit with the correct one for that engine, it will at least help you determine if it's a bad sender. After the new sender is in, if it still shows cold on the gauge, then you're back to square one.