Transmission warms up, then cools and takes longer to warm up

[RandomSquirrel]

So recently I started to notice that for the first 2-4min of driving (it's cold here in NOVA), the trans temp will warm up to about the 3rd "mark" (moving about 25-50mph), and then as soon as I turn to merge onto the highway, it instantly drops down to "full cold", and then takes another 5-10min to start to warm up again and then stays in the normal range. Is this "normal" behavior, or a sign of a possibly underfilled transmission and when I take a "harder" right turn, the fluid shifts and then fills the lines properly?

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[Nodak]

either that or a bad sensor?


i had a mechanical temp gauge in an old toyota i could tap the MID screen cover to make it flat line and tap again to go back to correct reading.

 

[RandomSquirrel]

With only 352 miles on her, I'd hope it's not a bad sensor. Lol But possibly worth a dealer visit if it doesn't rectify itself.

 

[Cranberry]

What your describing is 100% normal.

Heat in transmissions is generated through gear hunting / constant gear changes.

When you hit highway speeds the truck is likely sitting in the same gear while you cruise, thus not generating major heat that can be detected on the sensor. I assure you the transmission is warm and if you touch it, it will likely feel warn, its just not as hot as it would get if city driving or hunting through 4 gears constantly.

This is why “tow” mode downshifts the truck and keeps it in higher gears. To maintain a powerband area but also eliminating constant gear hopping that will generate heat and blow the transmission.

 

[Wahoo]

I have an SR5, which may have a different gauge appearance for the transmission than yours, but I generally drive with the engine oil and trans temp gauge screen showing, at least until it warms up (after which I switch to watching boost). In my experience, per the gauge my transmission temperature increases linearly, and I don't see swings like you describe (and certainly not a noticeable temp increase in the first 2-4 minutes of driving).

My morning commute is neighborhood/city roads for 5-10 minutes to start, and then interstate speeds for 10 minutes. It usually takes all of the first half of the commute for the trans temp gauge to get to halfway, where it generally sits.

Now, if I were really curious as to actual temperatures, I wouldn't rely on the Toyota gauges. I'd use a scanner.

 

[127.0.0.1]

Toyota transmission logic shifts differently when cold too, it will keep in lower gears until warmed up. Tranny ECU does all it can to prevent someone killing it but it can't prevent misuse

However all bets are off if fluid is actually low.

Real answer is to physically check fluid level and then go from there.

if you suspect it is low, then check it using the TIS procedures.

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