After swapping in a 4.3 I have decided to rewire the original coolant temp gauge, so I bought a new GP Sorensen sensor for the 85 toyota installed it in the 4.3 water jacket and wired it up to the old circuit.

It continued to show cold even when warmed up so I removed the plug and shorted across the two terminals and the gauge responded moving quickly to full hot.
That would normally be an indicator of a bad sensor so I decided to check the ohms at variuos temperatures and it seems to be within range. 1400 ohms at 80 degrees, 500 ohms at 160 degrees and 200 ohms at 200 plus degrees.
It seems strange to me that the gauge did not show full hot when I dropped the sensor in a cup of boiling water at only 200 ohms of resistance...
I have checked and double checked the continuity of both legs of the circuit and all is well I have a strong path to gound on one and a pulsing/flashing positive voltage on the other.
Any Ideas??

 

the sender you bought has two terminals?
IIRC, the gauge sender has only one terminal.

 

The sensor sold by Autozone and Advance Auto for this application
('85 22re) has 2 terminals. I have tried sensors from both with similar results,
the ohm range was the same and with the engine warmed up the needle was pointing to the bottom mark. they were slightly different in construction but had the clip on double terminal.
I am using a 2 wire terminal salvaged from the original wiring harness but cannot be sure if it was the correct one, but it appears to have been in the right location on the loom or at least close...

 

Might be that your guage requires a higher resistance value to bring it to full-scale reading. Did the guage come with literature that describe the full-scale requirements? You might be able to solder in an additional resistor (in series) to bring it to full-scale.

 

Stock gauge and sending unit, lower resistance equals higher gauge reading (ie.) installing jumper wire pegs the gauge.
but 200 ohms resistance at 180 degrees the needle barely moves..

 

If you've got a Radio Shack near you, pick up a 1K ohm variable resistor. Wire it up to the guage and find out what resistance pulls it up to 180 degrees. Subtract the coolant temp sensor resistance value at this same temperature. Set the variable resistor to this value and then solder it in series.

Having said that, it seems as though your stock guage is defective if paired with the stock sensor.

 

I was beginning to suspect the gauge was bad...
Good thinking with the variable resistor.. I have a Radio Shack 4 miles from my shop, thanks for the help.

 

sorry to piggy back on this thread but in my 81 22r my guage seems to work fine till it hits half then it wont go any higher. i really doubt that i have never heated the engine up past normal but i dont know why my guage would just stop at normal temp

 

Same thing mine was doing last summer, before the swap and before this current problem...