I bit the bullet and collected, via IR thermometer, the information I had been hoping I'd eventually see posted: Namely, pan temperatures taken from beginning to end of temp check mode. The verdict? When measured on the bottom of the pan (specifically, the rear portion, see pic) there's no temperature lag compared to fluid temps reported by the sensor in temp check mode. Ironically, readings taken elsewhere can show leading temps, but the bottom of the pan is pretty uniform and you can't really go wrong anywhere there. There were lots of measurements taken and I can now do it just by feeling the pan with my hand, but it all just basically confirms the sweet simplicity of SkylineGTRracer's method which leaves little room for improvement, but extra context never hurts so I'll write up what I found. The procedures below incorporate the instruction from the official docs about moving the shifter through all positions. I have no idea how important that may or may not be. In any event, the practical joke known as temp check mode is unnecessary.

I like aiming for the lower temperature range for various reasons. The difference between 97 and 115 degrees looks to be about 6oz of fluid or about 1.5% of total fill. Either one of the following methods is easy to do and reliably puts the truck in the lower range of temps with a little margin to spare. After fluid temperature stabilizes, it rises slowly at idle -- about 2/3 degree per minute -- so there's no rushing necessary at all. There was more data collected for the idling version, but the driving version should work just fine. See this thread for official docs.

(NOTICE: This was done on V8 which has external cooler. Can't imagine that matters much under these conditions, though. I should also mention that the fluid level produced by this procedure matches up with my original factory fill level.)

........Idling version.
With truck completely cold*, ambient temperatures mild, and transmission overfilled:
1. Start truck and slowly move the shifter through all positions before putting it back in park.
2. Leave engine running and let idle for 20 minutes. (Truck temperature gauge should be at operating temp between 10 and 15 minutes)
3. With engine still idling, pull overflow plug (5mm Allen wrench) and let fluid run until less than continuous stream.

........Driving version: Shaves as much as half the time off the above.
With truck cold and transmission overfilled:
1. Drive truck around the block until temperature gauge gets close to its operating temp position and head back to garage.
2. With truck still running, slowly move shifter through all gear positions and then back to park.
3. Let idle 5 more minutes, then pull overflow plug (5mm Allen wrench) and let fluid run until less than continuous stream.

If a level check is desired without overfilling transmission first, the graph should be of some use. Remove the overflow plug and wait to see when fluid starts to flow before replacing the bolt (and gasket). In the lower temperature range, the pan feels like someone's forehead with a fever. At 115 degrees, it's still easy to press a hand against the bottom of the pan and hold it there. At 125 degrees, it becomes obvious that it will soon become hard to leave the hand in place, if it's not already. At 135 degrees, the hand can be pressed briefly but I doubt many can leave it there.

Pan temperature rise for the idle test. Truck was *15hrs cold and garage temp was the same as pan temp. I presume the steep rise in the first 5 min is from residual system heat circulating through the pan.


Temperature reference spot in white. Numbers are approximate.

JB would you recommend this method for also changing out ATF & substitute using front trans line by radiator ? Did that make sense ? Mike

To each his own. I'm more comfortable using drains and fills.

Why I asked thanks

That is exactly what I did. I flushed out all the fluid by letting the tranny pump it out the cooler and I poured it back in at the same time. When nothing but clean fluid came out I stopped, connected the lines and check pan level. It was still a little low so topped it off to the check plug. Then ran it and checked the pan temp with an IR thermometer. I figured pan temp would lag a couple degrees so when it hit 95 degrees I shut it down and opened the check plug. About 3-4 oz came out, put the plug back in and all was done.

I like the scientifc approach to the methodology JB! Great write-up and confirmation of an old trick. I figured that measuring temps at the trans pan should yield the same result as a scantool since you have a relatively wide margin for variation.

Toyota has recently issued dealers with a new WS Fluid "gauge" to properly set the fluid in the transmission because of how many issues related to improper fluid level they've seen. Its really no more than a glorified go/no go gauge from what I saw in the online training course, I haven't seen one at our dealership yet (though honestly I haven't had to do a WS fluid change in a while, nor have I bothered looking for it.)

this needs to be added into our DIYs page

although I wont change it any time soon, but still I have to thank JB for the contribution

Good stuff. Very scientific and thorough as always, J.B.

Can we assume a ScanGauge is accurate enough as well for temperature checks? I'm assuming it reads the same sensor as the ECU when putting it in official "temperature check mode."

Gatafly - what method did you use to refill while flushing?

I'm planning to flush my trans in the next week and was thinking about disconnecting the trans cooler lines like you did, with the pressure hose going to an empty bucket, but placing the return hose into the fresh fluid. I can't think of any reason that wouldn't work, unless there's not be enough suction on the return side to draw the new fluid in. I just want a back-up plan in case it doesn't work...

Heres a good read to help you do it.

2006 4.0L Transmission cooler installation, with some pics. - Toyota 120 Platforms Forum

Some are worried about the different tools used for reading the temps of the fluid. The same fluid sensor is used via any type of tool. I have a Genisys OTC which gives me 2 temp readings. The input and output temp of the fluid.

Here is what I have wondered for awhile. What if the trans is at room temp. Do a drain and refill without any start-up. Replacing exactly the amount drained. Get the fluid in the temp window and check the level, if it is good to go then you are done.

I had some time to kill last week and did a complete pan drop, cleaned the metal screen/filter, dropped and cleaned the valve body and reinstalled everything back. Filled with fluid until it became a very small trickle. Entered the temp window and checked the fluid. I needed to add about 20 Oz. This was due to removing the valve body as it needed to run to pump the fluid into the VB. All is perfect.

I always like to drop my pans at least once every 60K for further inspection. Knock on wood I have put over a million miles on Toyota transmissions and have only had 1 failure. That one was on my 2001 RX300 which is known for weak tranny. It went out at 340K.

It will not suck the new fluid in. I had a friend help me and he started and stopped the engine when needed. I just put a large funnel hooked up to the return line and tried to pour it in at the same rate it was coming out. My friend was there to start the engine so I could pour immediately into the return line. If something went wrong he was there to shut it down right away. Went great and was only shut down when the new fluid came out. As mentioned I was only a few ounces low by doing it this way. I drove it for a day and checked again and it fluid ran out the check plug after only an ounce or two.

That's how I did my first two drains and fills, being very careful to account for all fluid.

Later on, a level check confirmed everything was perfect.

Great stuff @JB.

I'll be bookmarking this for later. Thank you sir!

great write up. The fluid level is checked with the engine running correct?