1981 FJ45 Troopy Temp Gauge Issue (1 Viewer)

[zolo]

I am having a very specific issue with a nearly finished project 45. As in its finished but the temp gauge is not working properly.
The truck can be started cold and if you run if once the choke is off and give it gas and rev it up the temp gauge will rise very quickly to full hot, even tho its still very cold.
We have tried different temp sensors with the same result.
We bought a new Gauge cluster, OEM brand new Toyota cluster and the issue persist.

What am I missing? It is not overheating, the coolant system is working perfect. The gauge appears to be responding to throttle response which I'm assuming has to do with charging volts when revved - or something else that I am overlooking. I've read the gauge cluster thread and could not find any mention of this type of issue.

Any help would be appreciated, This is the 45. This is the last detail before its totally finished.

 

[45Dougal]

If you think it's really repeatable, then disconnect the wire to the sender and clip your ohm meter onto the sender in its place, connect the black wire to the battery negative.
Now repeat your what you're doing and watch to see if the resistance changes.
If it doesn't change, then the problem is elsewhere.
If it does change, then connect the black wire to the brass casing and repeat.
If it now doesn't change then it could be the earth to the sender or the engine earth strap is loose.
If it still changes then you could have a much bigger problem inside the engine such as a leaky head gasket.

Another quick test is to disconnect the alternator and run only on the battery - could be a bad regulator for example.

 

[zolo]

If you think it's really repeatable, then disconnect the wire to the sender and clip your ohm meter onto the sender in its place, connect the black wire to the battery negative.
Now repeat your what you're doing and watch to see if the resistance changes.
If it doesn't change, then the problem is elsewhere.
If it does change, then connect the black wire to the brass casing and repeat.
If it now doesn't change then it could be the earth to the sender or the engine earth strap is loose.
If it still changes then you could have a much bigger problem inside the engine such as a leaky head gasket.

Another quick test is to disconnect the alternator and run only on the battery - could be a bad regulator for example.

Thank you for the ideas to follow up on, I appreciate it.
We tested the head gasket and it's for sure not a mechanical problem of the engine. The engine was rebuilt with all new gaskets and machine work done.

I will make the test as you stated and see what I come up with.

 

[FJ404345]

Nice FST Troopy !!

Can you add more pics plz