how to test temp sensor?

[skanthack]

anybody have a good test for a temperature sensor on my 72 FJ40? im not sure if ive got a bad gauge or sensor. ive had two temp gauges in and neither will register so im leaning towards sensor but before i buy a new one im wondering if there's a definite test. thanks

 

[ingomar]

I don't have a definative test, but here's an idea: the temp sending unit is a variable resistance device. Pull the gauge wire lead from the sensor. and put an ohm meter across the sensor wire connection point and ground; when mine was luke-warm ( maybe 120 degrees ) it had 175 ohms resistance to ground. If the circuit is open ( no resistance ) or if it does not change substantially between hot and cold, I'd say it is a bad sensor. Hope this helps.

 

[saryon7]

A quick test to see if it is the gauge is to just pull the wire off the temp sender and ground the wire against the engine. It should peg the gauge all the way when doing this.