Transmission Temperatures and How it Relates to Life of the Fluid

[mtbtim]

Hi Tim,

I just installed a tru-cool 4544 11"x11"x.75" cooler on my FJ cruiser and it does a better job of cooling than the bm 70264 I have used on other vehicles. Higher rated as well. The FJC never sees above 150*F on the highway. Its flat enough to fit bewteen the vertical support and condenser. The 4544 has 3/8" ports and fin and plate design.

Ideally you want the ATF temp between 130*F and 170*F

Thanks for sharing this. I'll take a look at it and maybe consider switching.

 

[19963.4lsr5]

I run the TrueCool 4589

The only thing that puts heat into the oil is the torque converter when it's not locked up or when its operating below its stall speed.

That's why locking out overdrive to get the RPMs up is recommended a lot.


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[ivopivo]

You bring up a valid concern about what the minimum temp should be. From my research, optimum ATF temps are around 170 F. The FSM says normal operating temp is 158-176. Even before I installed my external trans cooler, I would see temps in the 130's cruising down the highway on a mild temp day. The temperature your trans runs at depends on a lot of factors, ambient temp, speed of travel (air flow through the radiator and/or trans cooler cooling fins, strain on the trans (climbing grades), input from driver (turning OD off).

What most experts agree on is HEAT is the big killer of auto transmissions. Yes, having it run too cold all the time could allow moisture to build up in the trans and maybe the internal parts aren't lubricated as optimally at lower temps, but overheating your trans and not renewing the fluid on a regular basis are the real killers.

In regards to running too cold, external trans cooler manufacturers don't recommend bypassing the stock cooler in the radiator, especially if you live in cold climates because you lose some of the fluid heat transfer that happens with the trans cooler bathed in the hot engine coolant.

My B&M 70264 trans cooler allows my trans to run around 20 degrees cooler which can make a pretty big difference when you're climbing grades or towing. Since you're in Chicago with cold winters, your concern is legitimate. The coolers like mine have a low-temperature bypass that's suppose to divert the thicker fluid straight through cooler and not allow the fluid into the cooling fin channels until it thins out as it heats up.

That was exactly my point and that's the main reason I installed the aux cooler but didn't connect it yet. I wanted to simply test before/after, but my testing tells me that I probably don't even need the cooler. My trans fluid has only been changed once since I got it and that was just the couple quarts through the trans pan, not a full flush. I'm thinking with daily driving I'm hitting 180 max and usually right around 160, then with some offroad or mnt driving it goes up to 210-220 I can simply swap the fluid right after that trip and be good.

Since it's already on there I will probably just hook it up to the lines and see what happens. I'll be sure to report back.

 

[theriddler]

Old thread but lots of good info...wish i would have found this before. It's got me wondering if I should install this:

https://www.amazon.com/Tru-Cool-Long-Transmission-External-708-4739P6/dp/B008BTJFJ4

It's a tight squeeze but i have this TruCool 4590 installed:

https://www.amazon.com/Long-Tru-Cool-Transmission-Cooler-4590/dp/B005XZX8RY

When I here "heat kills transmissions" I think to myself: what are they calling heat? If that the case why would manufacturers run the tranny to the radiator to heat it up? I believe what they're calling heat is anything above the normal operating temps but they should state that...heat is a subjective term.

I'm going to abide by the service manual when it comes to the recommended operating temperatures and try to achieve that with the add-on thermostat I posted above...by the way the TruCool thermostat fully opens at 180 degrees which should be almost perfect.

 

[mtbtim]

Old thread but lots of good info...wish i would have found this before. It's got me wondering if I should install this:

https://www.amazon.com/Tru-Cool-Long-Transmission-External-708-4739P6/dp/B008BTJFJ4

It's a tight squeeze but i have this TruCool 4590 installed:

https://www.amazon.com/Long-Tru-Cool-Transmission-Cooler-4590/dp/B005XZX8RY

When I here "heat kills transmissions" I think to myself: what are they calling heat? If that the case why would manufacturers run the tranny to the radiator to heat it up? I believe what they're calling heat is anything above the normal operating temps but they should state that...heat is a subjective term.

I'm going to abide by the service manual when it comes to the recommended operating temperatures and try to achieve that with the add-on thermostat I posted above...by the way the TruCool thermostat fully opens at 180 degrees which should be almost perfect.

Well, it's excessive heat which lowers the effective life of the fluid and thus your trans. How long your fluid will last is directly related to the temperatures it's subjected to. Someone driving mellow doing around town driving could probably have their fluid last 100k. Then compare that to someone who lives in the mountains and is climbing steep grades each and every day. Their transmission fluid might be effective for only 20k or less.

Most vehicles don't come with transmission temperature gauges. They just provide an idiot light letting you know when you've totally overheated your trans. Most vehicle owners don't even wonder what their transmission temperature is. They just drive oblivious. It's only once you get yourself a scan gauge or use a bluetooth OBDII reader sending info to a phone app like Torque Pro do you start to understand the temperatures your trans is subjected to in different driving situations. I use to own a Honda Accord that I used to drive to mountain bike races. I would pile 4 dudes, their bikes and all their gear and then do drives like the 10 hour drive from San Jose to Big Bear Ski Resort that finishes with some pretty sustained grades. I know the trans temp must have been way the hell up there. The transmission on that Honda ended up starting to slip at around 200k and I know the punishment I put the transmission through had something to do with it.

 

[Drcoffee]

Old thread but lots of good info...wish i would have found this before. It's got me wondering if I should install this:

https://www.amazon.com/Tru-Cool-Long-Transmission-External-708-4739P6/dp/B008BTJFJ4

It's a tight squeeze but i have this TruCool 4590 installed:

https://www.amazon.com/Long-Tru-Cool-Transmission-Cooler-4590/dp/B005XZX8RY

When I here "heat kills transmissions" I think to myself: what are they calling heat? If that the case why would manufacturers run the tranny to the radiator to heat it up? I believe what they're calling heat is anything above the normal operating temps but they should state that...heat is a subjective term.

I'm going to abide by the service manual when it comes to the recommended operating temperatures and try to achieve that with the add-on thermostat I posted above...by the way the TruCool thermostat fully opens at 180 degrees which should be almost perfect.

When it comes to manufactures, its all about CAFE standards and mpg.
The faster the Fluids get up to temp the lower the mpg. The tranny runs most efficiently between 130-170. Adding a cooler usually wont make the atf lower than 150*F. Using the right cooler will allow the temps to rise to op temp without over cooling. The tru cool LPD cooler and the bm 70264 allow cooler atf to bypass the cooling plates and stay in the right temp range.. so it comes down to BTU efficiency. The bm70264 is 14,000 btu. The tru cool LPD4544 os 20,000 btu. That should keep you below the 200*F atf cooked atf level.

The LPD cooler does not need a special theromstat to operate. That is the beauty of it.

 

[Kotrin]

[MENTION=115088]theriddler[/MENTION]

[MENTION=78997]Drcoffee[/MENTION] had it right. The newer vehicles, especially the tundra's actually have a heater installed IN the transmission for MPG. The quicker fluid gets up to operating temperatures the better the transmission shifts along with increased MPG. I'm not talking like 5 it's probably even not even 2 but I'm not a engineer in this area. If it was electrical I would be better suited to talk about. It's the same with it being to cold. When I snow wheel I've actually put a piece of carboard in front of my cooler to help it out on occasion. I've learned a lot since I put in my Scangauge II and monitoring the temperature. City driving is the WORSE for my little transmission. I'll sometimes drive it as a manual to help it out.

The cost of bypassing is better than pink milkshake. Even if you put in a smaller BTU one it's still a benefit over the through the radiator in just keeping it from potentially going bad and unless you plan to replace the radiator.

Now all of this is from personal experience and what I understand. But just like a lot of people here I believe in preventive maintenance or preventive before it happens. Now I may have gone another 40K or even more but it was better to know I wouldn't need to worry about it versus oh I need a new transmission...

 

[theriddler]

[MENTION=115088]theriddler[/MENTION]

[MENTION=78997]Drcoffee[/MENTION] had it right. The newer vehicles, especially the tundra's actually have a heater installed IN the transmission for MPG. The quicker fluid gets up to operating temperatures the better the transmission shifts along with increased MPG. I'm not talking like 5 it's probably even not even 2 but I'm not a engineer in this area. If it was electrical I would be better suited to talk about. It's the same with it being to cold. When I snow wheel I've actually put a piece of carboard in front of my cooler to help it out on occasion. I've learned a lot since I put in my Scangauge II and monitoring the temperature. City driving is the WORSE for my little transmission. I'll sometimes drive it as a manual to help it out.

The cost of bypassing is better than pink milkshake. Even if you put in a smaller BTU one it's still a benefit over the through the radiator in just keeping it from potentially going bad and unless you plan to replace the radiator.

Now all of this is from personal experience and what I understand. But just like a lot of people here I believe in preventive maintenance or preventive before it happens. Now I may have gone another 40K or even more but it was better to know I wouldn't need to worry about it versus oh I need a new transmission...

Cool, that's very informative...I had no clue they put a heater in the transmission but i can see why they would. Everything is about mpg's and going "green" now...especially on a Tundra which probably struggles to hit 16 in the real world. I'm sure Toyota does it's best to give durability, mpg's, and keep the cost down...I for one would rather put up some money of my own and buy the external tranny temp and lose a mpg or two until the tranny gets up to operating temp. One tranny replacement is enough to last me a while

 

[BrianSD_42]

I do wonder if some of this thread is just paranoid. If you live in a city and don't off-road daily or tow and you change you fluid every 30k as instructed (drain n fill) then you should be fine.

Even getting a bit hot briefly isn't going to ruin the trans. I had my trans heat light come on only 2 times and both instances was a long slow 2wd crawl at low rps. I let the truck cool off for 15 and then kept driving but in 1st instead.

I have a 97 and don't even know my trans temps. Still going strong at 257K miles on original trans.

Now I have a trans cooler. Installed it about two years ago.

Btw IMO the trans heat indicator is a warning light, not a you're f#cked light. Toyota engineers chose to set it to go off at high temps as a warning to stop the engine because you are in the danger zone. But being in the danger zone does not mean that your trans is toast.

 

[mtbtim]

I do wonder if some of this thread is just paranoid. If you live in a city and don't off-road daily or tow and you change you fluid every 30k as instructed (drain n fill) then you should be fine.

Even getting a bit hot briefly isn't going to ruin the trans. I had my trans heat light come on only 2 times and both instances was a long slow 2wd crawl at low rps. I let the truck cool off for 15 and then kept driving but in 1st instead.

I have a 97 and don't even know my trans temps. Still going strong at 257K miles on original trans.

Now I have a trans cooler. Installed it about two years ago.

Btw IMO the trans heat indicator is a warning light, not a you're f#cked light. Toyota engineers chose to set it to go off at high temps as a warning to stop the engine because you are in the danger zone. But being in the danger zone does not mean that your trans is toast.

You're right that most people can get away with the 30k interval of a fluid change. But, for people who push their rigs and run higher than average trans temps on a regular basis, it would be prudent to renew it more often. I like the simplicity of drain and refills so I decided to do it every 10k to keep my fluid in good shape. For people who don't want to do it that often, do the complete flush every 30k or whatever interval your synthetic fluid is rated for.

You're right again that having the trans temp light come on isn't a death sentence for your auto trans but I also wouldn't qualify it as a nothing event. The "idiot" light comes on around 300 degrees. At that temp, you cooked your fluid really good and lowered it's effective lubricating life expectancy dramatically. When you get back home, it would be prudent to do a complete flush. Say this event happened just after you did your last flush, I certainly wouldn't wait another 25k+ miles for the next fluid renewal.

As for monitoring, if you were doing that while you were wheeling, you would have noticed your trans temp spiking and could have stopped well before the 300F mark. Waiting until the "idiot' coming on as an effective monitoring tactic is something I would never recommend somebody do. For people who push their rigs hard, I highly recommend you monitor your trans temps.

 

[octanejunkie]

Waiting until the "idiot' coming on as an effective monitoring tactic is something I would never recommend somebody do. For people who push their rigs hard, I highly recommend you monitor your trans temps.

Prudent and practical advice.

I got my trans fluid up to 280*F twice on a weekend trip not too long ago and let it cool with no ill effects, but I only knew about it because I was monitoring with Torque Pro. I did a complete flush after that weekend and all has been well since.

There is as much bad info about transmissions out there as there are bad transmissions out there, probably because most drivers don't maintain them properly or don't want to pay a shop exorbitant fees to do so - many seem to wait for problems to arise, then the cost is even higher. Don't be that guy/gal. Get proactive about your transmission's health and extend it's life.

 

[Kotrin]

I think I would rather have people concerned and educated versus the other. But you guy's are correct. People tend to panic just like the;
"I accidentally shifted into reverse when moving slowly or I shifted into 4wd, etc etc. "

But honestly if you maintained it and checked the radiator (that's my biggest fear and why I did my by-pass), changed it regularly, you'll be fine minus random previous owner mishaps. I'm glad I did it cause I see temperatures climb above 200+ and it allows me to better maintain the temp by OD or similar changes.

I've been thinking of writing a transmission article to try and clarify it, but this did a great job just needs some clarification/teaching is all. It helped me and even got some great knowledge from it Previous 4Runner was a 5th gen and before that was a manual so...I'll leave it at that

 

[ralfk]

I invested in bluetooth ODB reader + new android headunit which runs the torque pro app. I always monitor my temperatures on long trips or in hilly areas. I find that with OD on, the temp shoots up to 225F on sustained climbs. With OD off, i'm running about 20F cooler (~200-205F). So monitoring is key.

I usually keep OD on unless i see the temp climb past 200, in which case I have found keeping OD off is actually extremely helpful. I have not seen the temp climb much past 210F by city driving...even when stuck in traffic. Although bay area temperatures rarely go above 80F so your results may vary on ambient temps.

 

[octanejunkie]

I invested in bluetooth ODB reader + new android headunit which runs the torque pro app. I always monitor my temperatures on long trips or in hilly areas. I find that with OD on, the temp shoots up to 225F on sustained climbs. With OD off, i'm running about 20F cooler (~200-205F). So monitoring is key.

I usually keep OD on unless i see the temp climb past 200, in which case I have found keeping OD off is actually extremely helpful. I have not seen the temp climb much past 210F by city driving...even when stuck in traffic. Although bay area temperatures rarely go above 80F so your results may vary on ambient temps.

Seeing my trans temp regularly over 200 would make me uncomfortable. Where are you located?

Since I've started driving with TP and monitoring my trans temp, I turn OD off a lot. Most hills, OD off. In traffic, OD off. As a matter or fact, if the speed limit is 35 or lower, I keep it my 2WD Auto in 2nd gear to get the benefit of engine braking and higher rolling RPM - turns out it is also more fuel efficient (that's right) and I use my brakes less.

Contrary to the manual that came with the car that advises leaving OD on most of the time, I really only use OD on flat stretches of open road while traveling over 55 MPH and I find my MPG and fuel economy to be better than originally advertised on the factory window sticker. YMMV

 

[BrianSD_42]

As for monitoring, if you were doing that while you were wheeling, you would have noticed your trans temp spiking and could have stopped well before the 300F mark

Haha well I really would like to know my trans temps but I have been too lazy to install a 3rd party sensor and guage. I understand it is pretty easy though. I agree, definitely be concerned if the light comes on and be extra diligent about the fluid changes.

 

[mtbtim]

Haha well I really would like to know my trans temps but I have been too lazy to install a 3rd party sensor and guage. I understand it is pretty easy though. I agree, definitely be concerned if the light comes on and be extra diligent about the fluid changes.

Hey Brian, I added an aftermarket gauge to my 98. I didn't feel real comfortable messing with electrical because I had very little experience with it so I had my friend Mikey help me out. After doing this job, I've handled some other minor electrical things on my own and bought some tools to do it like a nice set of wire strippers, shrink butt connectors and a heat gun.

Here's the video of the install:

<iframe width="560" height="315" src="https://www.youtube.com/embed/fT_2szdKXRM" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

 

[19963.4lsr5]

I bought a cheep thermocouple sensor and pinched it between the hose and the cooler nipple and ran it into the cabin. If I want to look at temps I just plug it in and turn it on.


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[ralfk]

Seeing my trans temp regularly over 200 would make me uncomfortable. Where are you located?

Since I've started driving with TP and monitoring my trans temp, I turn OD off a lot. Most hills, OD off. In traffic, OD off. As a matter or fact, if the speed limit is 35 or lower, I keep it my 2WD Auto in 2nd gear to get the benefit of engine braking and higher rolling RPM - turns out it is also more fuel efficient (that's right) and I use my brakes less.

Contrary to the manual that came with the car that advises leaving OD on most of the time, I really only use OD on flat stretches of open road while traveling over 55 MPH and I find my MPG and fuel economy to be better than originally advertised on the factory window sticker. YMMV

I should rephrase, regardless of OD on/off, my temps are never above 200F on relatively flat terrain. However, on long sustained climbs (such as Sierras) with OD ON they do start to spike over 200F. I find that less common with OD off so I turn OD off when that starts to happen.

The main reason I did not keep OD off was because until recently i had a bad pinion bearing in the rear diff and it would get louder when coasting with OD off. I have fixed that issue so I guess I could try keeping OD OFF more often and see what happens.'

here's my setup with bluetooth ODBII + torque pro app:

 

[HeelAndToe85]

My B&M 70264 trans cooler allows my trans to run around 20 degrees cooler which can make a pretty big difference when you're climbing grades or towing. Since you're in Chicago with cold winters, your concern is legitimate. The coolers like mine have a low-temperature bypass that's suppose to divert the thicker fluid straight through cooler and not allow the fluid into the cooling fin channels until it thins out as it heats up.

I can't find data or literature that shows a low-temp bypass in the B&M 70264. Where can I find info on this? I want to run this in series with my OEM setup, but it is important to me that trans fluid gets up to temp normally.

For a data point / FYI:
For my 100% current OEM setup: Normally I see scangauge trans temps 205F or below for normal use. If I'm driving a ton on a hot day up to 210F. If I'm driving in mountains 230F. If I'm on steep mountain roads in 2nd gear at lower speeds (35mph) on a hot day I have seen 248F. 4LO offroading / rockcrawling I have never gotten over 210F.

 

[DK327]

I can't find data or literature that shows a low-temp bypass in the B&M 70264. Where can I find info on this? I want to run this in series with my OEM setup, but it is important to me that trans fluid gets up to temp normally.

https://static.summitracing.com/global/images/instructions/BMM-bm_cooler_techdoc.pdf

Check last page for "LPD" feature.