I have been using a Scan Gauge II since about May or June of this year. I bought it because we had a trip to Utah/Arizona planned for July, and since my FJ has only the standard transmission fluid cooler built into the radiator, I was a bit concerned about monitoring transmission fluid temps while traveling through some of the high mountain passes and hot desert countryside.
On the FJCruisers forum
, I found codes to monitor two transmission sensors in the FJ, and programmed the Scan Gauge accordingly with a TF1 and TF2 readout. The gauge I bought online from Gifford Automotive
came with a defective cable, but the supplier was very quick to send me a replacement.
I originally mounted the gauge above the steering wheel column, just in front of the instrument panel. However, I was not happy with that location, since the gauge blocked site of some of the idiot lights along the bottom of the speedometer. I then made up a bracket and mounted the gauge on the "hand grip" above the dashboard near the drivers side door.
This location worked out much better. Great visibility, easy to operate, and did not interfere with viewing of any of the dashboard gauges.
The auto transmission in my FJ has gears designated D, 4, 3, 2 and 1, and Toyota recommends keeping in 4th while towing. I found that non-towing (driving in D) in relatively flat terrain in summer type weather, the transmission fluid temperatures after continuous driving were typically in the range of about 165 to 180°F. While towing (in 4th gear) on relatively flat terrain in summer, the transmission temps typically stayed between about 175 to 200°F. I did notice really early that the transmission temperatures are about 10-20° hotter if I forgot to use 4th gear while towing and left the transmission in D. Apparently, this is because the torque converter is locked when driving in 4th.
Of the two temperature sensors on my transmission, one of them is much more sensitive to temp changes than the other, and tends to climb rapidly when the transmission is working hard. From posts by others on the FJ forum, it seems that this sensor may be located right at the outlet from the torque converter.
My highest recorded transmission fluid temperatures occurred while towing on a couple of very high mountain passes in Utah. While climbing up these steep mountain roads to near 9000 ft elevation, the transmission fluid temperatures would climb to the 220-230°F range. However, on one section of one pass in Utah, the TF temperature rose to nearly 250°F, which was beginning to worry me. Good news was that the temperatures always stayed high for only a few moments and dropped off very quickly when the transmission load was reduced.
The Scan Gauge has been a very useful tool in monitoring the TF temperatures and towing performance, and has helped me to understand much better how my rig is operating. Given that 99% of my towing is not going to be up-down high mountain passes in extremely hot weather, I don't really see that I will need to buy a secondary TF cooler for the FJ, and I think that I will continue as things are now set up. The Scan Gauge does have the added benefit of allowing you to monitor fuel consumption and mileage (and a host of other things) as you drive, which is quite useful as the FJ does not have stock capabilities to report those figures. It was well worth the purchase price and I am glad I bought it.