1971 FJ40 Temp and Fuel Gauge

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

H

henryporter

Joined
Jul 30, 2025
Threads
1
Messages
12
Location
fennario, PA
Hi All,
Hallelujah, Holy $hit, where's the tylenol.

I got '71 FJ40 this summer - drove it a bit despite really odd temps on the temp gauge. Temp gauge pegs high initially and drops after running a bit - a bit erratically. IR gun shows temps are OK - but I dedicated this winter to fixing the temp gauge. Temp Sender indicated no issues, but i replaced it anyway. Right or wrong, i leveraged Chat GPT for help. It led me to believe that the fuel gauge should be dropping voltage from 12 to 7v and the temp gauge requires 7v to operate properly.

So, i pulled the cluster, disconnected everything. Testing the fuel gauge output (fuel gauge, btw, seems to read proper levels), it looks like it has 12v coming off of it. Ordered a "new" fuel gauge and that too seems to be putting out 12v instead of the 7v that chat gpt is telling me to chase.

So, all that said, I'm really not sure if chat gpt is purposefully leading me down a wrong path or what. If anyone here can help validate that the temp gauge really does need 7v, that would be helpful. also, looking for confirmation that the voltage regulation should be embedded inside the fuel gauge pod.

Lastly, any other ideas or sources for new gauges would be so appreciated.

Happy Holidays to all.
 
Sort by date Sort by votes
Does your fuel gauge have 3 terminals? The centre 1 is the 5ish volt feed to the temp gauge. Guessing you have the earlier cluster and your temp gauge runs 12 volts.
Can fit the later fuel gauge into an early cluster and run later temp gauge/sender but then you'll also need the later fuel level sender.
Try a 12v temp sender first
 
Last edited:
Upvote 0 Downvote
Not sure what resistance levels a '71 uses for the temp sender, but if you are handy with electronics and have some resistors laying around, you can check the gauge cluster for accuracy based on the service manual specs, as it can be tough chasing your tail between the temp sender and the gauge cluster to isolate variables.

There are differences in temp senders between the year, with some having longer stems than others, that could also be leading to your issues. Measuring the outlet pipe from the engine with a laser thermometer like you did is a good idea. I have one that lives in my truck as I have yet to really trust the cluster readout... As several folks have said in similar threads, it's more of a "rough idea" gauge if anything.
 
Upvote 0 Downvote
Upvote 0 Downvote
procomsignathid said:
I believe this is the one. As always, double-check part #s. Ideally you can isolate the issue before you load the parts cannon:

www.cityracerllc.com

OEM Coolant Temperature Sender for '72 and Earlier Land Cruiser FJ40 FJ45

OEM coolant temperature sender for '58 to 9/'72 Toyota Land Cruiser FJ40, FJ45. OEM Part # 83420-20010.
www.cityracerllc.com
Click to expand...
GOod call. I've been testing on a new OTS sender but will buy this one too and try just in case that's the issue. Its cheap thankfully
 
Upvote 0 Downvote
Thanks for all the responses. Ugh. I've narrowed this down and realized chat GPT was indeed wrong. Fuel gauge is fine, but i replaced it anyway. No regulator in the fuel gauge and there isnt supposed to be one. Its the old style appropriate for a '71). I ordered a received a new (used) temp gauge and they are both demonstrating the same thing when tested with cluster removed on my bench:
1. Pegged high when de-energized
2. Running 12v (from an A23 battery) with temp sensor in boiling water: needle moves down to read "hot" but not pegged
3. Temp sensor in cold water - needle goes back up past "H" to peg
4. With temp sensor disconnected (open) it stays pegged high

I tried attaching battery to both posts and think I have battery connected to the correct post/stud.

At this point im just about to re-install the cluster with the new gauge despite the wacky readings. Before I re-install, thought I'd circle back for any smart ideas.

Wow this is fun but also a mystery to me. Perhaps two bad gauges? Seems unlikely

Will also test yet another temp sender from city racer. If thats the answer ill be relieved but also killing myself with the struggle of the cluster removal and pending re-install.
 
Upvote 0 Downvote
I went down a similar path, mine is a 78 but the thread might give you some ideas:
procomsignathid

Thread 'Water temp gauge t-shooting, advice needed'

Hello all- I am t-shooting a high temp gauge after replacing my radiator. During that process, lots of things changed:
  • New radiator
  • New hoses
  • New temp sender (used the one from City Racer, I also used teflon tape which I now know is a no-no)
  • Added a thermostat (was none there before), 180-degree
  • Added the stock heater back in (stock routing, no rear heater)
  • Flushed fluid and changed from green to red (this stuff)
For context, this is a 1978 FJ40.

Despite all this, my temp gauge has been consistently on the 3/4 mark of the gauge. I got ahold of a laser...
  • Like
 
Upvote 0 Downvote
procomsignathid said:
I went down a similar path, mine is a 78 but the thread might give you some ideas:
procomsignathid

Thread 'Water temp gauge t-shooting, advice needed'

Hello all- I am t-shooting a high temp gauge after replacing my radiator. During that process, lots of things changed:
  • New radiator
  • New hoses
  • New temp sender (used the one from City Racer, I also used teflon tape which I now know is a no-no)
  • Added a thermostat (was none there before), 180-degree
  • Added the stock heater back in (stock routing, no rear heater)
  • Flushed fluid and changed from green to red (this stuff)
For context, this is a 1978 FJ40.

Despite all this, my temp gauge has been consistently on the 3/4 mark of the gauge. I got ahold of a laser...
  • Like
Click to expand...
Many thanks for this link. oh boy. Pulling out a breadboard is probably the right level i need. I'll study your notes here and compare.
 
Upvote 0 Downvote
Amazing help everyone. So glad, sender number #3 was the answer. the original temperature sender from city racer above solved it. Occam's Razor of course. Appreciate all the help and hoping you have happy holidays.

No i discovered my entire vacuum transfer systems isn't working. On to the next one:)
 
Upvote 0 Downvote
You must log in or register to reply here.

Share this page

Back
Top Bottom