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Discussion Starter #1 (Edited)
Hi everyone,

When in February 2011 I was on the market for FJ Cruiser I thought what transition to get. Finally, I went with automatic, since it proofed to be reliable enough and no doubt much more comfortable in freeway and city traffic. Constant 4x4, which comes with manual transmission did not attract me, as I did not plan use FJ exclusively off roads.

There was one thing I did not like. It was dummy transmission fluid temperature warning light. ATF temperature is very critical for the transition. Overheating reduces its life down to few thousand miles, in extreme cases down to few minutes. For the off road vehicle it is important to monitor ATF temperature on the trail, where a torque converter is unlocked all the time and produces lots of heat. Very easy to overheat transmission, and even easier to overlook the light, us all drivers attention is on the trail.

After reading this forum and service manual, I discovered the light turns on when ATF reaches 302°F. This is already too late! At this point lots of bad things already happened in the transmission. There is plenty information about it in internet.

It become clear to me I want the ATF temperature gauge. I looked here and found good posts how to do this with analog temperature gauge and a sender. It involved cutting ATF cooling line to install temperature sender. I did not want to do this. I have 8 years Platinum Vehicle Service Agreement and I did not want to give Toyota chance to argue, that I altered the ATF cooling system. Well, possible reduce cooling line diameter and increase ATF flow resistance is not a good thing to do any way.

There are two sensors already in the transmission. Quick research showed me Toyota does not let us read these sensors over standard ODB-II interface. So, I decided to build something, which could read sensors and show result to me. There were many challenges, but few months later I designed digital temperature gauge and installed it. There are some pictures of it. Gauge has small Control Module, LED display and a push button.

I went with 7 segments LED display instead LCD display. Instruments should be easy to read. LCD is not us bright and reliable. I had choice of colors (yellow, red, blue and green). I have chosen red for a reason not to ruin night vision, but I think yellow is good too as it matches vehicle instrument panel design.

CM reads both sensors. I installed push button on CLUTCH START CANCEL switch plug (next to RSCA OFF) to switch between sensors. It also can switch between F and C. First digit top and bottom segments tell which senor is shown, apostrophe - measurement units. It turned out it was a good idea to read both sensors. First sensor is in oil pan, second - at the torque converter exit. It is very easy to see whether torque converter is unlocked by switching between sensors and observe temperature difference.

I also connected CM to parking lights to reduce LED display brightness when driving at night. It has two preset settings for day and night, which looks sufficient to me.

I am driving with the gauge 6 months now and I love it. First long mountains climb on freeway (no towing) caused ATF temperature rise over 220 degrees. To be honest, I did not expect it. Simple downshift from D to 4 helped me lock the torque converter and quickly brought temperature 40 degrees down back to safe area. During last half year gauge helped me many times keep transition temperature within safe range. I was surprised how fast and easy unlocked converter heats up transmission unsafe hot.

What is nice about the gauge, it does not interfere with vehicle at all. Being an electrical engineer, I made the CM inputs with very high impedance to ensure there will be no effect on vehicle ECM readings and transmissions shifting points. Also, it is very easy to disconnect three wires to eliminate any questions in case I will ever need any warranty repair.

Please, let me know you think about my mod. Any comments are welcome and much appreciated. I am not sure if I posted it in right place. If not, please, tell me where I need to move it.

If I see interest here, I can come up with a complete kit, which would require no soldering and very easy to install. Cut right size hole for the LED display, mount button and connect 5 wires are the only things an installer should be ready to do. I recommend mount LED lower than me, because I can see the reflection in left side mirror. I can write step-by-step installation instructions for the kit. The gauge should work fine on any car or tuck with A750 transmission, which is used on FJ Cruiser, Tundra, Tacoma, Sequoia, 4Runner, Land Cruiser, GX470 and LX470.







 

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Discussion Starter #6
Thanks all for your posts.
I know it is a hassle to cut the dash, but there are not that many places in front of driver for the box. You will not see the gauge under steering wheel or on the central console when you drive. Plus box will drive cost considerable up and even small box has to be bolted or glued to the dash for permanent installation.

When installing, you will need to remove some panels to rout wires under the dash to reach both sides of the vehicle.

Personally, I see no reason to remove this gauge in future. So, I decided to cut a hole. To my taste it looks cleaner. Many people use this place to mount extra instruments like pressure, fuel gauges, etc. And that left panel is very easy to replace any way.

One more. For convenience I made LED display wire with a small harness, so I can disconnect it if I need to.
 

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Great job and I'm interested put me on the list.
 

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Excellent mod. I'm interested. Let us know what a kit would run or if you're not interested in producing them perhaps just posting the schematic & parts list to assemble it. Thanks for sharing your work in this area.

Dave
 

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That's a very nice mod,great work you did there.
 

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I want one !:rocker: Great Job
 

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Very nicely done.

On my list is to add a supplimental transmission oil cooler with a spin on filter and a set of analog gages for the converter and trans pan temperatures.
 

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If you make one, I'm interested.


Sent from my Autoguide iPhone app
 

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Interesting. I thought of doing this myself. What MCU are you using? Did you calibrate the system? What thermo senors are you using? Are they thermistor or thermocouple based?

Yes, I'm an EE as well :wave:
 

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Redboat
 

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Very nice job 2011FJinCA but there's an error in your first post.

The high ATF temp warning light comes on at 239F, not 350F as you stated.

Normal operating temps for the A750F in the FJ are considered to be 122F to 176F.

The torque convertor stall speed is between 2,250 and 2,550 rpms.

DEWFPO
 
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