Temp Gauge 'flicker', 96 FZJ80 - 198k mi.. (1 Viewer)

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Was out on the Hassayampa yesterday in the sand and when pulling back onto the shuffleboard dirt road to head out, I noticed the temp gauge was flickering up and down from mid-point (normal temp) to HIGH - very unusual. Sand was fairly hard packed, and not a lot of bogging/slippage.


I immediately pulled over, and noticed that when the engine went to idle, the Temp Gauge needle immediately went to mid-point (normal) and was rock steady. Just to be sure, I opened the hood and checked overflow bottle, radiator cap, and saw no signs of overheating, whatsoever. Oil pressure was normal and level topped off before our last club meet, but checked that again to be sure - no problems there. Engine fan was working fine and pulling plenty of air through the radiator, no CEL, no loss of power, no signs of overheating. I wasn't running A/C either.


Got back on the road and noticed that if I accelerate, the Temp Gauge will peg to the HIGH range, and as soon as I let off the gas pedal, it immediately drops back to rock steady at the mid-point. Drove it gingerly across Carefree Hwy back toward I17, and replicated the behavior under steady state cruising (cruise control set at 2k RPM = 60mph). If you watch the needle, it actually ticks as it bounces off the HIGH limit within the gauge, flickering at a high rate as if it's mounted on a spring. Let off the throttle and coast = goes back to rock steady at mid-point. Step on the gas, and it pegs the needle at HIGH.


Took a good look at everything when I got home and nothing out of the ordinary. Checked it again on a trip today (freeway speeds), and exact same behavior. No other engine work has been done, haven't topped off the radiator recently (thinking air bubble near the sensor), and checked it multiple times today to be sure it's not overheating - and it's definitely not.


Thinking this is a Temp Gauge sending unit failure, but wanted to check with the group. Scheduled oil and filter changes, new head gasket over 5k miles ago, and the PO replaced the silicone oil in the engine fan for PHX temps years ago.


Any tips/suggestions/concerns appreciated,
 
Thinking this is a Temp Gauge sending unit failure



I would agree to start there. Most likely culprit, also check the connection at the sensor to see if it is getting good contact
 
I would agree to start there. Most likely culprit, also check the connection at the sensor to see if it is getting good contact

^^^ X2. If it were actually sensing temps properly, it could not make large, instantaneous moves that you describe. I would also look for a short/break in the wiring from the sensor. Good luck and let us know what you find. We all learn from each other. T
 
If you have a scan gauge or ultra gauge, hook it up and see what it says. If constant the it is likely the gauge or if it fluctuates too it may be the sender.

Sounds like something is not making a good ground or contact.
 
Haven't gotten the Ultragauge back from my brother, yet, but looked through the FSM the other night, and the Engine Temp Sensor is located between the 2 knock sensors and just above the oil filter. Easy enough to reach, and when I pulled the connector off, there was a lot of built up fine silt all around that part of the DS engine bay. Cleaned off the connector with some air and reinstalled until it clicked into place.

Haven't had a chance to get the LandCruiser out since to test it. Will report back when I have more info,

FSM image:
k37hci.jpg
 
No change - haven't gotten the Ultrascan tool from my brother, yet. As soon as I do, I'll be able to check the sensor output to the ECU. Haven't had the LandCruiser out of the tandem slot lately to see if my field troubleshooting had any effect.

I see there's another poster stating their Temp Gauge goes straight to 'Hot', so I'm hoping they see this thread, as well. Thanks,
 
Saw you online offering ideas about someone else's cooling issues and wondered if you solved this problem you were having
 
Nothing new, Sir. Still haven't gotten the Ultragauge back from my brother and other priorities have emerged. I'll post back with what I find, and hopefully it's just the connector to that sensor on the block. Thanks for asking!
 
Mine is doing exactly this. Literally exactly as he described it. Mines a 91 3FE. I’ll post my findings and keep you all updated on it

edit: just noticed this was from 6 years ago...
 
Mine is doing exactly this. Literally exactly as he described it. Mines a 91 3FE. I’ll post my findings and keep you all updated on it

edit: just noticed this was from 6 years ago...
It is also in the Copper State Cruisers subform ... so welcome from North Carolina!

Seeing as you have a 3FE, I would highly recommend the Koso slim gauge to monitor your coolant temps. I ran one in my 92 3FE for piece of mind (and maybe facilitating a little too much worry??). You can tap into one of the rad hoses, and put a sensor in the line to get a good reading. Good luck.

Also, as previously mentioned, check your water temp sending unit, It may be getting ready to expire...
 
As mentioned above, I pulled the connector from the temp sensor, cleaned it out, and the problem went away. No other cooling work required, seemed to be purely electrical. Good luck,
 
Replaced the coolant sensor for the gauge as well as the connector. No change. Got a 3 row aluminum radiator on the way as well as a new aisin thermostat. I’ve seen 1st gen tundras and 4runners do this 1000 times. Sediment will build up in the rad and not allow proper flow. Hopefully that’s my case. My fan clutch feels fine and roars like hell on start up so I’ll replace that last.
 
So after I replaced almost the entire cooling system my truck would still randomly “overheat”. The gauge is just broken. Today I didn’t make it halfway down the road on a cold start when the needle pegged red which obviously meant I’m not actually over heating since it was like 43 degrees out. But my koso gauge told me it wasn’t a hot air pocket from a head gasket issue or anything of that sort.

4B4DD685-4949-421E-AF21-9293099A2ED6.jpeg
 

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