Transmission cooler or not Thread

for the record - I learned something.

 

A couple of points that have influenced my thinking that lower RPM was more efficient.
First, in the Pacific Theater during WWII, Charles Lindbergh flew a few missions in the P-38. Twin Allison V12 engines boosted with either supercharging or turbo. ( Can't remember which one). He proved the theory of running over square not only didn't destroy the engine but increased efficiency. Over square is running at a manifold pressure higher than RPM ÷ 100. i.e., 30 inches of MP and 2,500 RPM. Or simply lugging the engine.
His aircraft was noted to require less fuel to refill upon return from a mission.

Second was a study done by BMW where they found the higher MPG was achieved at a lower RPM and higher throttle setting. But, this was a manual gearbox.

There are so many variables such as the decreased torque required in 4th on the Tundra or the most efficient RPM that my old way of thinking has changed.

Next trip south I'm just staying in S4 all the time instead of shifting to 5th as conditions permit.

 

None of this thinking is wrong. It has been proven right but in every case that you have listed above, the power losses through the transmission are the same. Not true going form a 1:1 straight power transfer to a level of gear amplification like overdrive.
In many cases you will get better efficiency at a lower RPM. You will nearly always make power more efficiently at higher throttle opening (this does depend on some other dynamics of your engine).
The point here is making power. Every engine has a sweet spot. This sweet spot will vary based on how far open the throttle is. The key is finding that sweet spot for the power that you need.
When you are poking a big hole in the wind at 60 plus miles per hour, you need to make a lot of power. Look at the torque curve of this engine. It makes peak torque at 3,600 rpm. That is where this engine makes power most efficiently. Now you are not running at full throttle so 3,600 rpm may not be the end game but am am sure that 2,000 is not
Rule of thumb. A gasoline engine turns gasoline into power at about 33%. If you need 150 hp to run your truck and trailer down the road you will need to burn 450hp worth of gas to do it. Give or take.
It is possible that your engine is more efficient at 2,500 but your transmission is less (it makes a lot of heat). So now your engine needs to make more power at 2,500 than you asking it to make at 3,100. Sure you are making power more efficiently but you are pumping that cheaper power to the front of your truck to your expensive cooler and litterly giving it to the wind. But we feel better because our engine is running slower and our transmission is running cooler
I think that the best answer would be some 4.10 gears in the rear. This would give me a few less revs in 4th for towing and a better overdrive for cruising empty. Maybe......?????? but on second thought, this OD seems to be a little high for the Toyota engineers comfort. They are very quick to let it downshift..... Maybe this is to protect the trans? Maybe it is more efficient to drop a gear than to push that much power through OD?

 

I just got my transmission fluid test results back from Blackstone. I'll try to post tomorrow after I blot out certain information to protect the guilty.

I will say that my transmission isn't being hurt by the amount of towing I'm doing and can extend my drain and fills out to 50,000 miles. I'll still do it every other year if I continue to tow 2k a year.

 

Here's the report and my letter to them. Don't know why my letter got scanned and saved twice.

So it look like the transmission doesn't mind a little work now and again. I normally make one trip down and back each year but had to drag the trailer home in January only to go back in February. So I'll continue to do the D&F every other year if I do the once down and back.

 

What fluid are you using

I can’t get the download on my phone

 

Good old Toyota brand WS.

 

See if this helps

 

Installed transmission cooler @ 42k miles and today did a drain and fill @ 43k miles.

Going out on a limb that this is the first one it’s had. Yikes.

 

One easy way to compare color between old and new is to put each in the same size tubing.

 

Very interesting reading, appreciate the input, commentary,opinions and facts.

 

Without a cooler staying in 4th definitely helps keep temps down, they still get hot but not as quickly or as high. With a cooler the temps stay the same in any gear.

 

No disagreement here. Watching and keeping temperatures in line is very good practice. However, if we only do that, we may not be doing ourselves or our trucks any favors.
We need to understand where is that heat coming from and why?
What are the advantages of running in a higher gear and making the heat?
What are the disadvantages of running in a higher gear and making the heat?

 

Perfectly red fluid in your transmission is not the goal. Your fluid changes colors because it is doing its job. This is not like gear oil.
Transmission fluid is design it carry contaminates, wear particles, water etc. It does darken as it absorbs this things. It is capable of carrying a lot.
Get an analysis done. It will probably show that the wear metals and other things that are being carried are well within the limits of that fluid.

 

We've just about proven you don't save much if any fuel towing in S5. Since my OCI is 5,000 miles I don't think running at a slightly higher RPM is going to reduce the life of the engine enough that I'll ever notice. I do know that towing in S5 with the torque converter locked will increase ATF temps slightly. About 10° F if I remember correctly. I always attributed this to decreased coolant flow at the lower RPM. Here of late it's proven that is only part of the reason.
One thing I can't see in the Blackstone report is the wear on the clutch packs and brakes. Since insoluble readings are 0 I wouldn't think that would be it.

 

I drove commercial trucks prior to my current career. And when I had a heavy load I would run lower gears than when the truck was empty. It allowed for more power and it put less strain on the drivetrain. I have seen transmissions practically “blow” off the truck from the torque because the driver didn’t know what they were doing (too high a gear for a climb with a load). Literally looked like the truck pooped out a transmission. I have seen many cracked fly wheels as a result of the same issue mentioned above.

Hence why I truly don’t understand the argument against not towing in a higher gear and/or overdrive…. Tundra or Mack…. Lower gear is better.

The motor can handle the higher revolutions far better than any transmission can handle extreme torque/heat IMHO.

 

I always have a hard time keeping the torque converter locked in S5.

 

Thank you for taking the time to post this video... It really helps having the visualization of what's happening w/the gears during the various shift points, but also explains why there are so many shift solenoids, etc and what they are each probably doing as the truck works it way through the gears...

So, I haven't towed anything significant w/my '21 yet, but my '08 saw a fairly decent amount of time towing a trailer about the size of yours... not having this knowledge or even blue tooth scan tool, etc. while driving, I based most of my driving decisions on the truck's behavior under various conditions. IE>>> If it was hunting for a gear, it wasn't being efficient and I quickly learned that I could mitigate that my remaining in S4 for the majority of time I was towing... (dumb luck I guess) But that's where it spent most of its towing time, and I had flawless service while towing and never had the transmission temp needle climb on me and the truck is still in service as it nears 300k.

Now, as look to possible towing on a regular basis again in the future (but w/the '21), I had been concerned about overheating issues due to the design change of these later year Tundras and had considered adding the cooler before I start towing w/it... This information is very helpful, and it gives me a more factual understanding of my vehicle's 'behavior' (while it had been towing in the past) in relation to transmission gear and performance; which leaves me a lot more confident about towing w/the '21 in OE configuration.

So, out of curiosity, let me ask this question... How does a gear swap (let's say to 5.29s on 35" tires) affect the efficiency of the transmission and it's gear ratios after the swap?? Is fourth still the most efficient, or does that change? I would assume it changes, but that's only based on what others have said about towing (and just driving unloaded) after a gear swap. They talk about less up/down shifting and gear hunting, and I assumed it was because the truck is staying closer to the 3,000 rpm range so that transmission remains more efficient??

 

On a level road with no headwind I could tow at 65 MPH with the TC locked. I think the turd shaped trailer I tow helps. Speaking of which, have you noticed some trailers that have a one piece nose section partially caved in while being towed? That and the membrane roofing with a big bubble? My Turd has a one piece fiberglass laminated roof that extends from the diamond plate aluminum in the front to the rear bumper. No cave ins or bubbles. Ugly but effective.

 

I had wrongly assumed that 5th was a 1 to 1 drive through the transmission and only 6th was the overdrive. . Pretend the paper sack is a dunce cap.

 

It seems like I have to keep my foot in it to keep the TC locked. So if I'm in S5, I can go 100 mph with it locked or I can go 60-65 with it unlocked. Or I can stay in S4 and watch the gas gauge go down.

 

Look into TS-B-0087-21. I had this done proactively. After the reflash I did notice slightly delayed TC unlock but towing and unladen.

Can't hurt to pester your dealer to do this. Quote the TSB to the service writer and of they blow you off like they did me, call corporate. That got me right in but the service writer gave me the stank eye and gave me the double stank eye when I demanded the under hood sticker to show it was done.

 

You are welcome. I am nerd about this stuff

S4 will always be the most efficient gear through the transmission. However, like you suspected the best gear for your speed may change. The hard part with big tires and a lift is the extra wind drag and the extra rotating mass. One pound of rotating mass is like adding three pounds anywhere else.

 

Clutch wear in these automatics is basically non-exsistant. The fluid does an excellent job of lubricating while providing enough friction.
I have also read that transmissions work best with slightly dirty fluid. The particulate matter in the fluid provides almost perfect friction for the clutch packs.

 

@mverkaik it's good to have you here and speaking for the forum, having you share your knowledge is greatly appreciated.
What are your thoughts on the aftermarket deep transmission pans that hold an additional ~ 3 qts ATF?
My sister who also owns a Tundra has a Doctorate in mechanical engineering specializing in heat transfer. Next time we talk I'm going to get her opinion on the benefits of the additional cooling of these pans. I have a feeling I'll get a lot of "It depends on ..." from her.

 

I'm going to chime in from the cheap seats:

I don't think more fluid is better or worse.

I truly think we should run the trans at a cooler temp than 195.

I recently got internet jumped for saying one should pin the thermostat open.
you know, to make it run cooler!
pinning it open dropped from an avg 200 (unpinned) to 165ish pinned.

the resident "Toyota engineers" were saying it would run too cool.


good grief.


get a trans cooler.

pin it open.

enjoy your transmission for years to come.

 

Thank you. I enjoy this stuff and have a passion to learn as much as possible.
More fluid will never hurt.
It will take longer for the mass to heat up. This is good and it is bad. Toyota did design these to run at 200 degrees and works hard to heat up the fluid.
It will hold more debris before the fluid needs to be changed. But if you are doing a drain and fill every 30k anyway.....????
It will take longer for the fluid that is in there to break down. But you are monitoring fluid temp and have proven that the truck is not going to cook it.
More pan area will provide some additional cooling benefits. But not much.

Worth the money? IMO, not for you.
Cool thing to have? Absolutely!
I would install the cooler before I would do this.

 

<hat tip> to your absolutely reasonable insight to this question.

 

Toyota wants this thing to run at 185 or more. That is why the thermostat opens at 185. That is why the pre-heat the fluid with the coolant.
Cooler fluid is thicker. Thicker fluid will not flow as well, will not pump as efficiently, and may not be doing all that you hope it would.

Nobody wants to pound on their engine till it is warm. The cold oil is not as effective as warm thinner oil. The same applies to the transmission. Fluid at temperature flows better and performs closer to the design intent of the transmission.

Now the goal here would be to keep the fluid as close to that 200 degree number as possible all the time. You can add a cooler to do this, you can run the trans in a friendlier gear to do this, you can drive less aggressively to do this. I would not promote pinning the T-stat open.

Just my two cents.

 

I have noticed that once we leave our wintertime campground on the Gulf we are on a 55 mph road. My transmission will not shift into 6th gear until the ATF reaches 100° F.