Water Temp Gauge Problem

[61n72cruisers]

My ’72 FJ-40 Water Temp Gauge does not work. The gauge is functional. The problem appears to be with the sending unit. I have tried both aftermarket and Toyota senders. On my gauge at rest, the needle is all the way to the right (Hot). As heat is applied to the sender, the gauge needle deflects to the left, or Cold. The warmer the sender becomes, the farther left the gauge needle moves. In other words, the warmer the water becomes, the colder the gauge reads. Without being connected, the gauge measures about 46 ohms across the terminals. Without being connected, the sender is open with no resistance. As the sender warms, it begins showing resistance, reading anywhere from about 130 to 190 ohms. It appears that at rest I need a sender that is in a normally closed position (dead short) in order for my gauge to function properly.
There are many pictures on Mud of instrument clusters, and at rest, some show the water temp needle all the way to the right and some show it to the left. I suspect there are different senders depending on what Toyota changed from year to year.
Thanks to Bj40green! He has a great posting on Mud which is very informative.
Can anyone please Help?

 

[FARMAN33]

**Not a technical reply**

I had this issue with my 72. At rest, not running it was pegged at hot. Start up and running it would move to the cold side. If I drove it for extended periods it would creep back to the hot side.

 

[Tim71FJ40]

Your best bet is to reach out to Rudi "bj40green" on this forum. He's the guage and wiring expert. Although I could have sowrn I read in one of his posts something about temp gauges and sending units being matched pairs by years, because some have oppostite polarity that causes what you're seeing.

He'll have the answer or a pretty good way for you to test what you have.

 

[DSRTRDR]

when not running, my needle rests at H as well [that's how this gauge works, I believe] - at start, swings over towards C, then adjusts as the engine warms up - most of the time, it hangs in the middle or slightly towards the H - I get nervous when it goes onto the third peg or beyond

 

[61n72cruisers]

Temp and Oil Pres Gauges

Thanks for the replies!

I may have it figured out, but won't know for sure for about another 10 days...that's how long it'll take Toyota to get the new sender in... my cruiser is a '72, built in September of 72, which is when Toyota changed the gauges as well as lots of other stuff. So it seems that my sender may need to be normally closed, instead of the one they first got for me, which is normally open... We shall see...

On another note, my oil pressure gauge was non-operational, but I got it to working! I had to remove the gauge, then the face plate and recalibrate it internally. Now it works perfectly, whereas before it wouldn't work at all! It was a simple fix, easily done

 

[Tim71FJ40]

From your temp gauge description it sounds like the same solution I read about. I think you're on the right track.

 

[bj40green]

Hi,
In Sept. 1972 Toyota changed from 2nd to 3rd generation clusters. See my thread -► https://forum.ih8mud.com/40-55-series-tech/544543-clusters-gauges-odo-meters.html
2nd generation clusters don't have the turn indicators in the speedo face plate. They are in the dash left and right from the cluster.
3rd generation clusters have the turn indicators in the speedo face plate.
From what I read you have a 2nd gen. cluster so the sender should be 83420-20010.
From what I've read in miscellaneous threads those units work as FARMAN and DSRTRDR describe.
Key in the "on" position but not running = needle at the H position.
When running and heating up the needle moves to the left.
I think you're fine unless you have a 3rd gen. cluster.

Rudi

 

[61n72cruisers]

rudi,
thanks!
the new sender will soon be in and i'll check the part number. it'll be about a week or more, but i'll post what happens when i try it. i do think i have a second generation cluster.
cal

 

[brtn540]

Thanks for the replies!

I may have it figured out, but won't know for sure for about another 10 days...that's how long it'll take Toyota to get the new sender in... my cruiser is a '72, built in September of 72, which is when Toyota changed the gauges as well as lots of other stuff. So it seems that my sender may need to be normally closed, instead of the one they first got for me, which is normally open... We shall see...

On another note, my oil pressure gauge was non-operational, but I got it to working! I had to remove the gauge, then the face plate and recalibrate it internally. Now it works perfectly, whereas before it wouldn't work at all! It was a simple fix, easily done

My oil pressure gauge is non-operational right now and I'm trying to fix it. I'm a newbie on most of this stuff so what do you mean by "recalibrating it internally"?

 

[flaa1a]

OP

You may want to read through this post. I struggled through the same thing you were and may getting ready to be! Hopefully it will be of some help....

https://forum.ih8mud.com/40-55-series-tech/520085-changing-temp-sending-unit-help.html

 

[61n72cruisers]

sorry it's taken awhile to reply...i've been fishing

anyway, to recalibrate the oil and water temp gauges for my '72 cruiser, i carefully removed the gauge face plate (be cautious of bending the needle or knocking it off - it's quite delicate). notice that fine wire wrapped around a thin band of metal (actually, it's a bi-metal). check the ohms to make sure the wire and connections are intact. there are 2 "arms", both with pivot points and serrated teeth at one end. one arm determines the sweep of the gauge, the other i believe is for sensitivity. both arms can be adjusted (carefully!) by inserting a small screw driver in the teeth and through the small hole in back and slightly turning either R or L to move the arm(s). when i calibrated mine, i had the senders hooked up so they'd read correctly.

 

[61n72cruisers]

The internal adjustment is hard to describe, but here goes...

CAREFULLY remove the gauges from the cluster via the 4 screws on the back. Then CAREFULLY remove the gauge face plates WITHOUT knocking the needles off. There is a saw tooth looking end on the arms inside of the water and oil temp gauges. The arms can be adjusted by CAREFULLY inserting a small screwdriver to engage the saw teeth and through the hole and CAREFULLY turning one way or the other. I had my gauges hooked up to the senders and a 12v battery on a bench when I did this so as to accurately calibrate them. Now they work perfectly!
Let me know if this helps, or, ha ha, I can try my best to say it in other words....

 

[MuskieFJ]

I also have a 9/72 FJ40 but my gage starts at the left then climbs to hot but almost always pegs hot until I'm idling at a stop light then drops to within temp range. Any idea which temp sending unit part number I should have? I have the "short" sending unit now if that helps.

 

[61n72cruisers]

I also have a 9/72 FJ40 but my gage starts at the left then climbs to hot but almost always pegs hot until I'm idling at a stop light then drops to within temp range. Any idea which temp sending unit part number I should have? I have the "short" sending unit now if that helps.

For my '72 FJ-40 (made 9/72), at rest (cold) the gauge reads all the way to the right, or H, and the sending unit that Toyota designed for it is normally closed (reading a dead short with an ohm meter). When the key is turned on for starting and current is instantly applied, the bi-metal strip inside of the gauge is instantly warmed causing the needle to deflect to the left, or C. As the sender warms, resistance decreases, causing less current to be transmitted to the bi-metal strip inside of the gauge which in turn causes the needle to deflect to the right, indicating a higher engine water temperature. In 9/72, or right around there, Toyota changed the gauge and sending unit functions to be the opposite (my presumption is so that full current would not always be applied to the gauge at start up). When Toyota changed the units, the sending unit is normally open (infinity on an ohm meter) and the gauge at rest reads C. As the engine warms, resistance begins to increase from the sending unit, sending current to the bi-metal strip (inside of the gauge), causing the needle to deflect to the right, or H. The warmer the water, more resistance from the sender, more current is transmitted to the gauge and the farther the needle deflects to the right, or H.
This has been a puzzle for me, I had to basically figure all this out for myself by piecing together bits of info, so I hope that my explanation helps more than it confuses...

 

[MuskieFJ]

Makes sense to me. Thanks for the explanation and clarification. As stated I have been having problems with my temp gage always reading hot and since we both have the same build month and year Cruisers (9/72) was wondering if that could be the problem with mine. Mine starts cold and then climbs past operating zone and then stops at H. Is there any adjustment on the back of the gage to lower?

Since on my phone I can't see the earlier posts referring to rebuilding gages and can't remember if that was covered. If so I apologize for a repetitive question. Thanks again for the clarification.

 

[61n72cruisers]

Makes sense to me. Thanks for the explanation and clarification. As stated I have been having problems with my temp gage always reading hot and since we both have the same build month and year Cruisers (9/72) was wondering if that could be the problem with mine. Mine starts cold and then climbs past operating zone and then stops at H. Is there any adjustment on the back of the gage to lower?

Since on my phone I can't see the earlier posts referring to rebuilding gages and can't remember if that was covered. If so I apologize for a repetitive question. Thanks again for the clarification.

Your gauge can be internally calibrated as I described in a previous post, and since you say it reads hot, I would DEFINITELY CHECK IT. If your engine is actually running hot, at idle or other speeds, you have another problem which needs to be immediately addressed.
If I was you, I would remove the sender from your engine head and calibrate the Toyota gauge on a bench using a separate, after market gauge (with an actual face that reads degrees) in conjunction with your Toyota gauge to calibrate it correctly. Otherwise, you can do the same using the sender installed in the block, except that it's easier to artificially warm the sender (as in immerse it in a cup of water heated in the microwave) with it removed.
Regardless, to correctly calibrate your FJ's gauge, you must access the gauge's guts, so you must first remove your instrument cluster and then remove the gauge from it.
Let me know how you get along with it. I'll talk to you on the phone about it sometime if you need to.
Cal

 

[MadoneRider]

76 engine, 72 gauge

Hi,
In Sept. 1972 Toyota changed from 2nd to 3rd generation clusters. See my thread -► https://forum.ih8mud.com/40-55-series-tech/544543-clusters-gauges-odo-meters.html
2nd generation clusters don't have the turn indicators in the speedo face plate. They are in the dash left and right from the cluster.
Rudi

Thanks for the thread and I read the other one too... Specific question. I have a '76 2F engine in my April '72 FJ40 2nd gen cluster. I bought a new 76 sender trying to match the block (before I read your thread) and it seems to not be operating properly (pinned right - you can't see it at rest) goes normal when warm but then creeps hot even when the engine isn't. If I buy the matching '72 sender it seems from pictures that the sender is much longer. May be a dumb question but would that restrict water flow or bottom out in a '76 2F block? Would it be easiest to replace my gauge or buy the older sender? or should I get crazy and try to adjust the settings of the gague like you pros do

Thanks much P.S. this is my first shot at a post

 

[Waterboy]

You have to have a sender that matches your cage cluster. Here is how mine was done. '75 2F with a '70 gage cluster. Just raised it up using an adapter.

 

[bj40green]

Hi Madone,

You can't change the temp gauges. The pre 72 is fed 12V. The later one is fed 7V from the internal VR from the Fuel gauge.
Do as Waterboy showed in his pic's. Raise the sender a bit by using an adapter.

Rudi

 

[MadoneRider]

Thank you

Awesome, thank you both and the pics help a lot! I'll pick up the older sender.