1985 FJ60 Coolant Temperature sensor / no reading on dash!

[RECRUISER]

OK guys I really want to get this fixed. There is no reading whatsoever on my coolant temperature gauge. All the other gauges work perfectly. Here is what I have done so far. I removed the wire with the female terminal connector that is attached to the water temperature sensor located on the top of the motor on the carb side of the head and grounded it to/ on my firewall. When grounded it in this fashion the temperature gage obediently pegged all the way to the top. So I know that the dash gauge is working, and that there is continuity in the wire from the dash to the coolant temperature sensor. So all that was left was to replace the sensor itself, so I ordered an aftermarket one on eBay for $10. After installing it I went for a drive thinking I had solved my problem but the temperature gage did not budge at all again!

What else could it be?

So my question is... since my dash gauge works and there is continuity in my wire to the sensor itself would you buy another water temperature sensor? Or is there another piece to the puzzle that I have not considered? Those temperature sensors are such simple units you wouldn't think it would be possible to get a bad one but I may be wrong to assume this.

Thanks anyone want to take a stab at this? I would appreciate being pointed in the right direction.

 

[OSS]

Throw that POS $10 eBay temp sender in the dumpster and buy the correct one from Toyota.

To test where 239° F is on your gauge, get a 27 ohm resistor & wire it inline with the temp wire to good body ground.

Make sure the sender is making good metal to metal contact with the head. You can verify with an ohm meter set to continuity with one probe on the sender body (not tab) and the other probe on shiny grounded metal on the head.

A new Toyota sender will read about 41 ohms when placed in 212° F boiling water.


This document has more info about the temperature sender than you'll ever want to know.

 

[RECRUISER]

So you are pretty much in agreement that the $10 sensor is the culprit. I was pretty confident that was the problem so I was very surprised when it didn't budge on my test drive. Thought maybe I was missing something. If anyone else has some input it would be highly valued thank you. And yes I deserve to take some heat over buying the $10 sensor. If you feel that is all that it is, or could be.

 

[OSS]

Heat up (run) the engine 10 minutes then measure the sender's resistance while it's still installed in the head. The resistance should be less than 80 ohms. If it is... Then either the gauge wire isn't making electrical contact with the tab (unlikely) or the gauge is bad.
You can test the gauge with resistors. Details are in that calibration doc above.

 

[RECRUISER]

Very helpful to have that Additional information. Thanks again for your help and interest.

 

[hygge]

Very helpful thread. I've replaced my sender unit and will be trying to follow these testing steps set out in this epic 150 page PDF. This is closer to a PhD paper on water temperatures than the FSM. Many thanks!!

 

[FJ40Karl]

Throw that POS $10 eBay temp sender in the dumpster and buy the correct one from Toyota.

To test where 239° F is on your gauge, get a 27 ohm resistor & wire it inline with the temp wire to good body ground.

Make sure the sender is making good metal to metal contact with the head. You can verify with an ohm meter set to continuity with one probe on the sender body (not tab) and the other probe on shiny grounded metal on the head.

A new Toyota sender will read about 41 ohms when placed in 212° F boiling water.


This document has more info about the temperature sender than you'll ever want to know.

This is unrelated to this post but I don't know how to start a new thread:

I have a 69 FJ-40 and recently had an 85 FJ-60 2F motor installed. The water temperature sensor is reading backwards on my gauge on the dash. I read that if you use an 85 sensor for the motor the dash panel for my 69 reads backwards and I have to order the tempurature sensor for a 69 F engine. I have the new part but the sensor is about 1.25" longer than the 85 sensor and will not retrofit into the shorter extension in the current block. If I could get a longer extension piece it would fit. Is there such an extension piece? Really dont want to install in the radiator hose.