Hi guys,

2000 SR5
222k Miles
All maintenance up to date, including new radiator, trans flush with Valv. Max Life, etc.

Stock 3.91 gears (was a 15" wheel truck)
Running 33" tall tires with these gears (yeah, I know, it's an absolute dog)


I live in a relatively flat part of NC- no strenuous hills or rough terrain on my daily commute. With regular driving, my scangauge is often hitting 212-220 degrees trans temp. Temps will usually hover 190-200 as the norm, and on cool days, 175ish


Do you guys think my 16" steel wheels and 33" tall MT's are stressing the trans out, resulting in the high temps? May be time for a re-gear...

You are gonna need to define this better...

How fast, constant or changing speeds, stop lights, OD on or off, etc.

Don't freak out at 200*F trans temps. Keep up on the fluid changes and you'll be fine. ~180*F is better, but 200*F is not death!

-Charlie

Regular driving here can be defined as a mix of 70mph on the interstate, some stop and go (never much), and 50mph on back roads -- OD on in all of these cases. In all of the previously mentioned cases, 210+ regularly occurs

I've seen some charts from Trans companies like TCI that mention that 200 deg is nothing to be afraid of given you're changing your fluid regularly. However, just not sure if it's "normal" for a 3rd Gen.

Trans temp varies a huge amount with speed, incline (load), and gearing. My typical transmission temps, once fully warmed up, are something like this:

Steady freeway cruising @ 70MPH - 150-165F
Stop and go traffic - 180-195F
Climbing hills @ 30-45 MPH - 190-210F

I've noticed that OD really plays a huge part in trans temps, as does which gear you're in, and to some extent speed.

For example, I notice that if I cruise at 40 MPH, my trans temps are higher than if I cruise at 47MPH or so. In fact, I might be cruising at 40MPH and see temps such as 180F, then accelerate slightly to say 47MPH, and immediately see the temps start dropping to something like 165F. The reason being is that the torque converter has locked up and is no longer slipping, which generates heat.

Anything you can do to keep the torque converter locked is a good thing. Keep speed up, turn off OD, manually shift the transmission down to 2 or even 1 depending on the condition. Or, in extreme cases, where possible, use 4LO.

This past weekend I was exploring a forest road that climbed from ~3000ft to about 6500ft over about 10 miles. This was a one lane paved road with little traffic. When leaving the transmission in D and the transfer case in 2wd, I was hitting trans temps above 210F going about 25 MPH. So I stopped, shifted to 4Lo (with center diff unlocked on my 2002, so it's safe to do on pavement). I resumed, doing the same speed, and my trans temps instantly dropped to 175F or so.

All of this is with stock tires and gearing, a new factory radiator, and about half refreshed ATF with MaxLife. If you're seeing significantly worse temps than this, I suspect either you're underfilled on the transmission, or your tall tires are causing your gearing to place a lot more load on the trans/torque converter.

Replace your fan clutch, Timmy has a video. At speed it won't make a huge difference due to all the wind but while going slow it sure will.

Talking about the transmission temps here

Good suggestion for high coolant temps though! Given the troubleshooting of the fan clutch is done, they're not always the culprit

Steady state cruising with the torque converter locked should have the trans temps around 80-100*F above ambient.

The torque converter will lock under light loads in 4th/OD above ~50mph and more aggressively above ~45mph in 3rd (OD off). (4.10 gears and 31"-32" tires)

The trans temp reported by the ECU is the HOTTEST the trans fluid gets, before the cooling circuit in the radiator.

-Charlie

This is a valid and important point. My 2011 Tacoma had two temp sensors/readouts available via Scanguage. One was in the same place ours is, and the other was what people called the "pan temp", which was clearly after the cooling circuit. The pan temp when the torque converter was locked was the same as the other sensor, but when the torque converter unlocked and the sensor in the same location as our is spiked, the pan temp would be sometimes 50F lower.

Your stock transmission cooler IS the radiator. It connects on the bottom of the radiator and transfer heat to the coolant itself. It is very relevant since lower coolant temps = lower transmission temps.

Lugging around in low RPM's under high load can directly affect it, especially since you have small gears and larger tires on top of it. A re-gear is rather expensive though just to lower trans temps 20 degrees.

Turn OD off completely for a whole week and monitor your temps. If they do go down, consider either keeping it off full-time or re-gearing. Or lowering your coolant temps!

Figuring out how to drive with the torque converter in lockup is key to a happy trans temp. I personally like the oil in the pan temp over the temp the 4Runner looks at which is the converter outlet temp.

I’ve driven 32 miles home already and had temps around 30 degrees above ambient. I have a medium sized trans cooler in Series with the cooler in the rad.

I use my temp gun to measure the oil pan temp when I get home. It’s never been out of my comfort zone.


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OP, your trans temps are way too freaking high for the conditions you stated. Something is not right. Like others have mentioned, are you monitoring your coolant temps also? If so, what coolant temps are you running?

Have you checked your fluid level when on level ground, engine running, trans at operating temp and you are within the hot range of the dipstick. Operating temp according to the FSM is 158-176. When I do a drain and refill of the trans pan, I dial in the level by getting the trans up to 180 degrees and then top it off until the level is equal to the top hot mark. The way you can get your trans up to operating temp without driving it is you have the parking brake on, left foot on the service brake and right foot on the accelerator, and trans shifter in Drive. Bring the rpms to around 1,000 while you are monitoring the temp with your scan gauge. Once you hit 180, put the trans in Park and quickly jump out and check the level.

You should not be anywhere near the 200's cruising down the interstate or anywhere else for that matter unless your driving grades or towing. Yeah, your transmission is fine driving in the 200's but your fluid life is going to be much shorter. What I would be worried about is what kind of temps would you hit if you drove in the mountains. If you're seeing 200's with mellow driving, your temps are going to be through the roof when you really start pushing your rig.

Turning off OD is very helpful to keep the trans temp down but I normally only use this trick when I'm climbing grades that put me at a speed between 45-65 mph. If you're driving slower than 3rd Gear, turning OD off does nothing for you. If you driving faster than 65 mph, your going to be taching out your rpms turning OD off. I've never had to rely on the OD trick to get my trans temps down when driving on flat interstates or city streets.

So, long story short, I'm not in agreement that everything is hunky dory with your trans. What you are seeing with your trans temps is far from normal.

You learned a good lesson. I learned the same lesson one day climbing some steep fire roads and I was in 4hi. Switching to 4lo made a huge difference with my trans temps and I've been preaching this to people I wheel with, on the forums and on our YouTube channel. Heat is the killer of auto transmissions. I tell people they need to monitor their trans temps even if it means they have to install an aftermarket gauge like I did on my 98.

Thanks for the thoughts here, Tim- Really enjoy your YT Channel, btw!

Coolant Temps: They hover around 195 Degrees in most cases. Sometimes they'll shoot to 198-199 in stop and go traffic, and peak up to 204 degrees in intense 90+ degree weather in heavy standstill/creeping traffic

Since my current TB and WP is 9 years old, I am doing that job this weekend with thermostat (with jiggle valve in correct spot), idlers, etc to see if it makes any difference (it's due maintenance anyways).


My trans fluid levels are fine, and the fluid is not burnt, etc. I am really starting to wonder if the steel wheels and heavy BFG KM2 combined with 3.91 gears is heating the trans up under even mellow operating conditions. 4.56-4.88 may be more ideal

Those coolant temps are acceptable, so it's not the coolant that's keeping the trans fluid hot.

Because of your large tires and smaller gears, you've gone essentially from at 29.5" tire (unless you had those small 225/75/15s on there!) to a 33" in tire so your speedo is off, which in turn will also mean your RPMs stay very low. Low temperatures plus high engine loads equals a lot of heat and stress on the transmission.

Another thing I should mention is to keep the ECT Power button on full-time. It raises the shift points up a few hundred RPM's and will hold higher RPM's a bit longer under moderate throttle, which also will keep trans temps a bit lower.

I know this because I have to deal with heat in my transmission but because of extra power. The previous owner fried the last transmission due to too much heat transfer from the supercharger, so I've had to take steps to reduce heat as well. Turn off OD, turn on ECT Power, do your normal drive and report back on temperature changes.

Your coolant temps are high. Either your jiggle valve is pointing the wrong direction or your fan clutch is getting tired. But, those coolant temps wouldn't explain how high your trans temps are. It might just be due to your gearing and tire choice.