WTSU Resistance readings

[crash1964]

Hi, my wtsu in my 1978 2F is reading 358 ohms cold (85f) and 68 ohms on a hot engine with no movement at all on the dash temp gauge. Are the ohms readings I’m getting in spec?
Bad connection behind the gauge or bad sending unit?
Thanks.

 

[charliemeyer007]

You should look in the manual free downloads Land Cruiser Factory Service Manuals (FSMs) - https://www.cruisercult.com/factory-service-manuals

Sensor is varying so the no meter movement points to the meter and its wiring as the issue. Ground would be my first guess.

 

[crash1964]

You should look in the manual free downloads Land Cruiser Factory Service Manuals (FSMs) - https://www.cruisercult.com/factory-service-manuals

Sensor is varying so the no meter movement points to the meter and its wiring as the issue. Ground would be my first guess.

Thank you.
That does make sense. I’ll pursue wiring etc.
I do have one other question. I noticed that there is a 3/4” x 1/2” bushing in the head and sensor installed in bushing. I’ve read there’s a long sensor and a short with short being for 1978. Do you think this setup would matter? After all it’s still in the coolant jacket.
Thanks

 

[charliemeyer007]

I think the resistance ranges is different between the two sensors/senders. Your gauge will only work correctly with the proper sender. It also needs functional wiring. You can test the gauge and the wires.

 

[pb4ugo]

You can turn the key on and ground the wire at the sender for a short eriod of time and see if the gauge needle moves. Or there is a testing procedure described in the fsm using a specific watt light bulb.

 

[crash1964]

pb4ugo, that was great advice and a simple check. I got the warden to watch the temp gage rise as I grounded the lead to the sender. Gage and wiring are good.
I reckon the wrong sender is installed or it’s just bad. It’s brand new as the rebuild was done in late 2024 and it’s now got about 65 miles on it since I took position in late September 2025.

 

[Engineer8000]

The early long senders are not variable resistors, they are point type regulators and function the same way as the oil pressure sender and early fuel level senders. You cannot test them with an ohm meter and get meaningful results. You can use a test light and test the same as the oil pressure sender, the light will pulse on and off.