Hey I recently got an ultragauge and have been monitoring the trans temps. First off I’m wondering what’s a normal operating range for trans temps and engine temps? My engine temps usually don’t go higher than 190 but at one point on a hill climb they were up around 202 for a second. The trans temps are all over the place but sometimes with overdrive on and when I’m engaged in 4th gear the temps would always rise and once got up to 215 before I noticed and let off. So I’m wondering why do the temps increase so much when it’s in 4th gear and they drop as soon as it downshifts into 3rd or up shifts into 5th. And what’s the point I need to worry on trans temps?


Sent from my iPhone using Tapatalk

Its all about the friction.

When the torque converter is locked up, there isn't extra friction. 3rd is locked up. 4th is locked up until you ask for more acceleration then it can unlock in 4th and start generating that extra friction, you can see when this happens because the rpms will rise slightly but not as much as they would if you had downshifted. Press the pedal a bit more or disable overdrive and it will downshift to 3rd and lock up again and you will see the transmission temp immediately start to drop to normal.

LOTS of answers to this in these forums:

site:toyota-4Runner.org/3rd-gen-t4rs/ transmission temps - Google Search

Your 5th gear is actually the torque converter locking up in 4th. When the torque converter locks up or the engine RPMs are above its stall speed (somewhere approaching 3000) it’s hardly making any heat.


Sent from my iPhone using Tapatalk

Your engine temps going up to 202 are nothing to be concerned about.
190 is "normal" but it could be at 202 for a long time and still be fine.

My Toyota Factory Service Manual (year 2000) shows the normal operating temperature ranges as:

- 158-176 F for ATF
- 176-203 F for Coolant

Huh, my UG recently reported 249(!) degrees trans temp on a loooong, slow desert dirt climb and the A/T Oil Temp light didn't even come on (it works at start-up). My trans temp is all over the place and often runs hotter with OD on than off. I can be cruising on the freeway at 70 at approx 2K engine RPM , turn OD off and drop the tranny temp 10 degrees while running at 3k engine RPM (not saying they are related - just saying). My Trans oil is still red, smells good, and is smooth to the touch. I will be doing the filter and a fluid drain/replace soon anyway.

To be honest, you are probably better off not monitoring your temperatures. Everything you've stated is normal operation for a used vehicle with 150K+ miles on it. I think you'll drive happier NOT knowing what the temps are.

The engine temperature gauge will start to rise past halfway at around 230 degrees. That's when you need to be concerned about the temperatures. I've hit 230-240 on two separate occasions due to part failures with no long term damage though as it was very brief. Transmission temps have to be very, very high to turn on the A/T Oil light on the dash.

I think the FSM trans temp range is for the oil pan temp. Not the fluid temp as it leaves the trans.


Sent from my iPhone using Tapatalk

Interesting. Thanks for the info. Seems odd to me that the FSM would list a temp range for the ATF at a location that’s different from where the thermometer is located (and thus reported by OBDII). I’m not saying you’re wrong, only that it seems odd.

I had always just assumed the OBDII temperature data was the correct data to be used when using the FSM to perform temperature-specific diagnostics and procedures.

I’d love to learn more about this..

Could this be a FSM difference between earlier 3rd gens that don’t report the ATF temperature via OBDII, and later 3rd gens that do?

Totally agree - shit makes no sense. Just take good care of your fluids and filters. My engine runs nice and cool in all conditions. Transmission temp is bipolar.

It makes no sense why they would post an unrealistic temp range. I personally think it more important to see the trans pan oil temp. That is the oil after the cooler and what helps maintain the internal parts temperature. The sensor is sensing the fluid temp as it leaves the torque converter. It is the highest heat load, most variable and the last item in the fluid path before it leaves the trans if I understand the hydraulic schematics correctly.

Unless you’re *****-footing it on flat roads and running in lock up all the time it be tuff seeing the temp at that sensor constantly below 176f.


Sent from my iPhone using Tapatalk

That's a reasonable 'normal' range for coolant, though engine damage won't start until much higher than that. When the cooling system is 100% working, it will almost always be between 188*F and 193*F unless the situation is extreme.

The trans temp is the range used for checking fluid levels, but it will vary quite wildly from that. There is no thermostat or anything to help control the trans temps. The trans temp light on the dash will come on at ~285*F/140*C.

The temp sensor for the trans is on the fluid outlet to the cooler. That's why the temp drops so quickly when the torque converter locks.

-Charlie

Yep, the TC is the highest heat load and the last in the path because of it.


Sent from my iPhone using Tapatalk