Transmission Temp Gauge Install w/Pics

#1
This is what I finally did to install a transmission temp gauge. I know a lot of people have installed senders in the lines, and other various places, all of which are nice set ups, but I wanted something simple and easy. I wanted to install the sender in place of the drain plug.

The problem is the drain plug is M10x1.5. It’s a pretty small plug and after spending almost a week and countless hours searching the web and visiting a local instruments supply store, I came to the conclusion that there was only one temp sending unit on the entire planet that was that size. And there were no adapters in that size to mate to any other sender.

The sending unit is from VDO, part No. 323-091. And I had a hard time finding it. It’s not a common sender at all, but I finally tracked one down. The sending unit matches up with VDO transmission temp gauge part No. 310-107. The problem with this gauge is that it has a range of 150-400 degrees, whereas our transmissions generally run under 200 degrees. To make matters worse, the gauge face basically has 150-200 degree range as the first two hash marks and the 200-400 degree range make up the rest of the gauge range. (See pic in second post) So, most of the time, the needle is going to be setting near the low point.

On the other hand, if the needle is anywhere but the low point, there’s no mistaking that the tranny is headed for trouble. So, in a way it's a glorified idiot light. But at least I'll know the tranny is headed towards overheating before the light kicks on at 300+ degrees.

VDO makes two other temperature gauges. One with a range of 100-250, intended for water temp and one with a range of 120-300, intended for oil temp. Neither will work with this trans sending unit, even though VDO advertises all their sendings units as being 10-180Ohm range. I tried. They end up reading way to too low.

To install, I just removed the stock plug, and drained out almost exactly 5 quarts of tranny fluid (a lot more than the 2 quarts the manual says for some reason). I then installed sender. The head of the sender is smaller than the drain plug, so I couldn’t use the stock crush washer. I made a washer that fit, but I’ll be checking to make sure it doesn’t leak. The number of threads on the sender is the same as the stock drain plug. The sending unit itself protrudes another approximate inch into the pan.

By the way, does anyone know if the stock A/T oil temp idiot light is suppose to come on and then off with the ignition switch like most of the other lights? Because mine doesn’t come on at all. But I definitely have the stock sensor.

Pic 1: Draining the fluid. Strangely 5 quarts came out, even though the book says only 2 should have. But I see this is pretty common from other posts. I took the oppertunity to put back in 5 quarts of Mobil 1 ATF.

Pic 2: The new VDO sender in place. Fortunately, the sender is pretty well protected, so the chances of it getting damaged off road is not huge.

Pic 3: Shows the Land Cruiser A-pillar pod I ordered from "egauges.com". This is an Autometer part. Part no. ATM-15413. Fits the 2-1/16 size gauges. I painted it grey to sort of match the interior. It's shown here with a 100-250 VDO water temp gauge I was experimenting with.
 

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#2
The VDO transmission temp gauge installed and running at operating temperature (just driving around town for about 15 minutes, at low speeds and with an ambient temp of about 45 degrees.)

Looks like here the oil in the pan is running at about 175 degrees. It's actually a little less as the angle of the gauge makes the needle look like it's reading just a touch higher than it is. Probably closer to 160. Now that I think about it, the range on this gauge is actually fairly useful. The only time it would be necessary to pay attention to the gauge is when it's reading between 200-300 degrees and there's a pretty wide range there. Beyond 300, the idiot should come on and damage is probably being done to at least the fluid.
 

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