Ever wonder how fast your auto tranny can overheat?

Ok yeah, that's the only times it unlocks for me

 

Add a lift and some 285s and it will do it all the time.

 

When I added my 31s, sometimes it will downshift over a causeway we have here

 

I read my temps thru an obd2 bluetooth reader and torq app on my phone. I have also added a slightly bigger trans cooler and it doesn't go thru the radiator anymore. Went a step further and did a tranny shift kit. To increase pump pressure and flow. It operates great but still likes to run higher temps. I take it out of OD anytime im climbing grade. And flush the fluid often.

 

The trans losses efficiency as the gears increase. When in OD, the engine is spinning slower than the wheels and the efficiency of your torque converter is abysmal. You loose MPG's and your fluid heats up very quickly. They invented the lock up clutch to fix this issue with automatics. If you remember the 3.0, the auto trans didnt have a lockup and tended to explode (too much heat).

So yes, when you unlock the internal clutch in the TQ, the fluid will heat up very quick. This is why I try to drive at highway speeds with the TQ always locked.

When towing/hauling heavy, turning the OD off will keep you in 3rd gear and allow the trans to lock up the TQ in 3rd gear. This will keep you from shift searching and unlocking the TQ clutch all the time and save your trans from overheating.

 

See mine never seems to lock the TC in 3rd with O/D off. It's just gets to 3rd and stays there. That's why I have always towed with O/D on

 

The heat comes from converter slip not the trans clutches slipping. All converters slip when they are not in lockup the higher the gear the more they slip add a trailer and they slip even more. Normal driving with no load in the bed or a trailer the trans should be fine with any generated temps. Disconnecting the radiator cooler is a bad ideal this will actually make it hotter particularly in traffic with no air flow. The cooler is in the coldest part of the radiator it is returned cool water to the engine.

 

The question I have is what is real "overheating" temperature in Toyota's transmission?

Sure you can see the transmission running 220F when not locked, and lower when locked. Is 220F a problem? Probably not.

I drive a stick so can't experiment, but a 500 rpm increase in unlocked OD is still lower rpm than downshifting to 4th and likely will get better mpg in OD

 

Wow, Lots of misinformation here. With the OD off button pushed it does in fact LOCK the torque converter in 3rd. That is why you should never tow unless on flat ground in OD.

 

At 220* you are still ok. Any higher and fluid starts breaking down.

Also with the torque converter unlocked you are loosing HP with the slip in it. So, your mpgs would be going down as its not transferring all the available power.

Also keep in mind that the A/T temp light doesn't come on until the tranny hits 300*. At which point you've already cooked the tranny and fluid, and severely reduced the life of it. That is why a temp gauge is so important.

I have seen these trannies do 500k miles if taken care of and not overheated. That is behind Lexus 1uz motors pushing 270hp as well. They are very strong trannies, but need to be taken care of.

 

Pushed in your talking about? It's a 4 speed trans w/ O/D. With o/d off it only goes up to 3rd. When o/D on it will shift to 4th and then at 46 it finally locks the TC(O/D). That's how my truck shifts at least

 

3.0L did have a lockup TC . It was just so low on power that it never got a chance to actually lock up. Lol

 

With the OD off button pushed. It locks the TC in 3rd. Without it pushed, the TC will lock and unlock in 3rd and 4th at any speed. Allowing more heat to build up.

The point is, watch your temps. If they get above 215, hit the button. They will drop a degree per second. Its pretty simple.

 

At least it should. Mine did

My bad you're right, 340h did have a lock up.

 

I'm just confused on what is meant by the TC locking in 3rd with the o/d button pushed. With my button pushed off, the trans just goes to 3rd and stays there. With it pushed on, it will then shift to 4th and finally lock the TC at 46 mph, dropping the rpm 500

 

OK, so I take see now that the TC will lock in third with O/D off. At highway speed it downshifted to third, then dropped about 250 rpm, which i assume would be the TC locking

 

Would running synthetic atf in these transmissions help resist over heating and burning the trans fluid? Does synthetic have a higher burning point than conventional?

 

From what Ive been told it helps a little, but not like oil. Trans fluid is mostly already synthetic, and its more of a hydraulic fluid then a lubricating oil

 

Where is the O.D. off button?
2014 trd auto.

 

Dont know on yours. Usually they're on or near the shifter though