Background: '85SE 2M6 3.4l

With the installation of my 3.4PR ( with new water pump) I replaced the temp sensor ( by the distributor) and installed a Rodney Low temp 200*-210* Fan Switch (by thermostat), installed new thermostat. 195*. & rewired the Temp Gage/Over Temp light in dash panel.

Tests performed: Fan switch grounded... turns on Fan.. Temp sending wire harness ground test Battery power on. left side Temp Light on, Right side Temp Gage pegs in red ......All Good!

All wires attached.... Ignition "On".... Over Temp Dash Light on. (bulb check)

Problem:

Start engine; coolant comes to temp .....gage hits 240 or so thermostat opens...(Hot water to front radiator and return hose).. gage continues to Red Zone. Fan never kicks in and Over Temp Light never comes on ! Coolant Fluid never flows out.

Bad sensor from TFS ?? Gage side of sensor only is there a resistor I am missing?

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Mark
' 85 2m6 3.4PR
In the Great Northwest!

Bad temp gauge calibration and the engine never overheated.

Calibrate the temp gauge and try again.

http://www.fierosails.com/tempgage.html

Thanks PhoneDawgz... How did I miss that in the instructions....... maybe it was the 6 months between swap and install

Thanks again .. going to Radio Shack as we converse.

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Mark
' 85 2m6 3.4PR
In the Great Northwest!

NP

No fan - but you know the wiring is good and the switch is new

No light - but you know the wiring is good.

No boil over.

Temp gauge is in the red.

Three of these things say one thing and one says something else. That's what makes me suspect the temp gauge calibration. The pegging throws it off. It's my guess but it does make sense. Calibrate and either prove that it is the problem or calibrate, find out it was on, and find out it is not the problem. At least it is a step or 1/2 step forward.

I'd have to agree. Your thermostat would be opening well before 240 anyway.

I tested the Gage with the ohm values provided. the gage was spot on. Are there two sensors built inside the Sensor Unit?? one for the light & one for the gage?

If not I cannot explain the gage hitting 260+ and the light not switching on... Manual indicates a bad sending unit if gage tests good... So I will be off to O'Reilys for a new unit..

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Mark
' 85 2m6 3.4PR
In the Great Northwest!

[This message has been edited by NW-Fiero (edited 11-23-2014).]

quote Originally posted by NW-Fiero: Are there two sensors built inside the Sensor Unit?? one for the light & one for the gage?

It's all explained in that link in Phonedawgz' post. One pin for the light and one pin for the gauge.....but they were the wrong pins from the factory.

So Gall757 from an engineering aspect you are saying that there are 2 separate devices built into the Temp Gauge Sending Unit and not just one device that has 2 functions.

Thanks.

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Mark
' 85 2m6 3.4PR
In the Great Northwest!

quote Originally posted by NW-Fiero: So Gall757 from an engineering aspect you are saying that there are 2 separate devices built into the Temp Gauge Sending Unit and not just one device that has 2 functions. Thanks.

I don't know how they did it internal to the sensor. One pin is a threshold ON/OFF for an idiot light, and the other is resistance for a gauge. Maybe someone has cut one open and can tell us.