Help w/ temp sending unit and fan.

[scubachris]

Hey y'all,

Been trying to get my fan working and have replaced the fan switch and bought an aftermarket fan. Never could get it to turn on and was using dash gauge to measure temp. Turns out the dash gauge was off and so I replaced it. Verified by using two different laser temp readers. Gauge reads 260ish laser reads 160 by sensor and same on top of radiator. The bottom stays at 130ish.

1) what's up with my gauge/sensor that two do the exact same thing. I'd think my gauge would be off.

2) should my radiator have a 20 degree difference from top and bottom?

Thanks

[spider2081]

there are 2 senders in the head. One is the temperature sender and the other is the over temperature switch that is suppose to peg the temp gauge if the temperature exceeds about 240 degrees. Sometimes the wires to the senders get reversed. Also if the over temperature switch is failing it can make the temperature gauge read higher than it should. I would disconnect the over temperature switch when engine is hot and see if the gauge indication changes.

[scubachris]

there are 2 senders in the head. One is the temperature sender and the other is the over temperature switch that is suppose to peg the temp gauge if the temperature exceeds about 240 degrees. Sometimes the wires to the senders get reversed. Also if the over temperature switch is failing it can make the temperature gauge read higher than it should. I would disconnect the over temperature switch when engine is hot and see if the gauge indication changes.

Thanks
The only one I know is on the couch coolant line. Where is the other sensor?

[vandor]

If you have two temp senders (resistors) instead of a sender and a switch (on/off) the gauge will read high.

Basically if you disconnect one of the wires the gauge should read right.

[scubachris]

If you have two temp senders (resistors) instead of a sender and a switch (on/off) the gauge will read high.

Basically if you disconnect one of the wires the gauge should read right.

Thanks, did it and they are bad. I've already ordered two.

[4uall]

fyi

https://www.youtube.com/watch?v=8DtcIlkt4BY

[scubachris]

fyi

https://www.youtube.com/watch?v=8DtcIlkt4BY

That is the best post ever. Thanks!

[spider2081]

According to my wire diagram for 1980-82 spiders the overheat switch should be a gray wire with black trace. The temperature gauge wire should be a green with black trace.

[So Cal Mark]

the wires to the senders can be swapped, the gauge will read the same. As for the temp drop across the radiator, it should be cooler at the outlet than the inlet but only 10-15 degrees. If you see a huge temp difference that points to the radiator being plugged up