A good auto transmission question:

[Mighty690]

I've been meaning to post this question for a while now. It pertains to a recent reading of my 1993 Owner's Manual regarding shifting the transmission. When climbing a steep and steady grade in my 80 I am prone to dropping it into 2nd. Revs increase, throttle position decreases. Engine seems happy and I'm happy. BUT, the Toyota manual states that one should not climb or load the engine for prolonged periods in 1st or 2nd. It says that it should be left in drive for such prolonged, extreme duty (overdrive off, of course).
I've never rebuilt an automatic transmission and tend to be suspicious the contraptions in general, so I'm not an expert on them - well, not that I'm an expert on ANY part. (I'm one of the guys that would have bought one with a manual transmission if I could have.) I would like an expert to mechanically explain the above "leave it in drive" admonition.
Thank you!
(Exact quote will be found in post #6.)

 

[wrongway around]

Ya funny how little is known about the a442f tranny.
I've found if you want to save the tranny from overheating out of lockup you have to keep the revs up,but thats not the best for the motor. I would never own an 80 without a tranny gauge hooked up at the tranny output line.
Plus i doubt Mr toyota would ever say that you can get lockup in any gear just by over riding the solenoid. But im definitely no expert either.

 

[scottryana]

You want to know what my nonmechanical guess is? They were worried people would forget about it in 2nd and run it to redline for extended time. Running it at 3500-4000 is probably fine.

 

[Mighty690]

Hmm... interesting thoughts. Thank you. When I talk about 2nd gear hills I'm talking about between 3000 and 3500 RPM. In the meat of the torque curve, everything good. But I digress; there must be basis for that statement in the manual. If I wasn't so warm and comfy right now I'd go outside and get the manual and make a direct quote from it regarding this "leave it in drive" thing. Maybe tomorrow.

 

[wrongway around]

Around where i live the busy time for truck tranny rebuilds is hunting season, slow low revs in drive. At least thats what the tranny guys tell me.

 

[Mighty690]

Okay, here's the direct quote from the manual:
"Do not continue hill climbing or hard towing for a long time in the "2" or "L" position. This may cause severe automatic transmission damage from overheating. To prevent such damage, "D" position should be used in hill climbing or hard towing."

 

[Mighty690]

Funny: the manual also says that maximum allowable speed in 2nd is 67mph! Can't imagine doing that...

 

[SmokingRocks]

thats bouncing off the redline basically.

Where are you towing for extended periods of time in 2nd or 1st? I certainly hope its not on the interstate.

Sounds like their main concern is that there won't be enough cooling air passing over the trans cooler / radiator at that speed. Which would cause the transmission to overheat and potentially the engine as well. If you are doing this a lot I'd install an additional tube and fin transmission cooler and a gauge so that you can make sure you aren't going over 220 degrees.

Better yet, get a truck that is designed for towing and put the 80 on the trailer.

 

[elhombre]

Sounds like another great reason to upgrade the fan clutch with thicker fluid to keep everything nice and cool.

 

[UWdave]

Ideas on why Toyota would not recommend extended 2nd gear runs under heavy load:

- Maybe the torque converter doesn't lock in 2nd under load??? The lock helps keep the transmission substantially cooler.

- Maybe low cooling flow when in 1st and 2nd gears? Every trans is different, but maybe the pump isn't driven well in those low gears??

- Could be a high heat gearing combo?? Unlike manuals that have individual set of gears for each speed, autos use different combinations of locked/unlock planetary gears. (interesting side note: Allison 1000 5 and 6 speed transmissions are mechanically identical, the 6 speeds just have another mode) Maybe 1st and 2nd use a rotating ring gear which causes more heat.

 

[Mighty690]

thats bouncing off the redline basically.

Where are you towing for extended periods of time in 2nd or 1st? I certainly hope its not on the interstate.

Sounds like their main concern is that there won't be enough cooling air passing over the trans cooler / radiator at that speed. Which would cause the transmission to overheat and potentially the engine as well. If you are doing this a lot I'd install an additional tube and fin transmission cooler and a gauge so that you can make sure you aren't going over 220 degrees.

Better yet, get a truck that is designed for towing and put the 80 on the trailer.

I'm not towing at all, in fact. This is just a technical question. When I'm climbing in 2nd, it would be the same speed as if I were in Drive. The engine and throttle position would appear to be superior climbing in 2nd, but the manual doesn't indicate that's good for the tranny.
The last time I can recall doing this was climbing up the grade into Death Valley. Hot + altitude + it was very scenic, so we were just cruising along enjoying the experience. Dropping the rig into 2nd, engaging cruise control and keeping my head up was a great way to go. The engine, with its new fan clutch and rebuilt radiator and head gasket, wasn't going to overheat anyway. Still, why does the Owner's Manual say to keep it in Drive?

 

[Whileemptyheadsdream]

All parts are moving faster, more friction, same airflow over cooling tubes. Heat Is a killer

 

[Tools R Us]

Okay, here's the direct quote from the manual:
"Do not continue hill climbing or hard towing for a long time in the "2" or "L" position.

Define "long time", if the grade is say, 6 miles long and you are going 60mph, that is ~6min, is that "long time"?

This may cause severe automatic transmission damage from overheating. To prevent such damage, "D" position should be used in hill climbing or hard towing."

At least on mine, if the throttle is matted on a steep grade the trans will drop to 2nd, it's in the factory programing. Depending on grade, it will sometimes hunt between 2nd and 3rd, so I hold it in 2nd int gear that I prefer with the shifter.

My guess; the manual is written for the world market, all of the USA market rigs came with a very nice/large cooler, not true of other markets. On USA market rigs, I have never seen anything temp wise that I would consider concerning, and we go uphill often in desert conditions.

 

[Tools R Us]

Funny: the manual also says that maximum allowable speed in 2nd is 67mph! Can't imagine doing that...

I routinely do steep grades at 60-65mph indicated in 2nd gear, it's ~4000-4500rpm, right where the motor makes the most power, it's a non-event. Mine has stock gears and 37" tires, so corrected that's ~72-78mph.

 

[Tools R Us]

...
Sounds like their main concern is that there won't be enough cooling air passing over the trans cooler / radiator at that speed. Which would cause the transmission to overheat and potentially the engine as well.

When running the motor at fullish throttle and ~4000rpm, it's making max power, so also max heat, but: When turning that rpm the pumps are making max fluid circulation, fan is blowing at full potential, the rig has great air airflow around it, so is cooling at full potential. If fully loaded, lugged down at say 2500rpm, not so much.

If you are doing this a lot I'd install an additional tube and fin transmission cooler and a gauge so that you can make sure you aren't going over 220 degrees.
...

The factory cooler is well setup to take the load, have you looked at it? It's huge in comparison to most aftermarket coolers.

 

[Heckraiser]

I am also a little baffled by automatics, but everything I have read on mud and elsewhere seems to indicate the transmission is happier and cooler being left in 2nd gear for a hill climb compared to jumping back and forth between 2nd, 3rd and OD. The engine makes more noise, but I'm confident the 'ol FZ can take 4k rpms for a few minutes if needed.

 

[Whileemptyheadsdream]

I have a theory. The lack of power In our rigs and our attempts to make up for that lack of power causes the heat that blows the head gaskets. I wonder If there is a way we could record as many H/G replacements as possible and see there association to hot climates and hills and Increased heat we are talking about here. I still think the bottom line here is Its a heat Issue. I apologize If this has been done already I have only been reading here about a year. Thank You !

 

[Whileemptyheadsdream]

thats bouncing off the redline basically.

Where are you towing for extended periods of time in 2nd or 1st? I certainly hope its not on the interstate.

Sounds like their main concern is that there won't be enough cooling air passing over the trans cooler / radiator at that speed. Which would cause the transmission to overheat and potentially the engine as well. If you are doing this a lot I'd install an additional tube and fin transmission cooler and a gauge so that you can make sure you aren't going over 220 degrees.

Better yet, get a truck that is designed for towing and put the 80 on the trailer.

This last sentence Is sadly very true. I talked to my son about this saturday, these trucks are just not designed to pull trailors. You can load them up and go anywhere, but I read all the time how difficult It Is for people pulling trailors especially on grade. You run the risk of heat related damage. Good Post smoking !!

 

[SmokingRocks]

When running the motor at fullish throttle and ~4000rpm, it's making max power, so also max heat, but: When turning that rpm the pumps are making max fluid circulation, fan is blowing at full potential, the rig has great air airflow around it, so is cooling at full potential. If fully loaded, lugged down at say 2500rpm, not so much.

There is a point where faster circulation actually becomes more of a detriment rather than benefit. The fluid is not able to cool to its full potential as it is getting pushed through the element too fast. Also as the element gets heat soaked its efficiency drops. I'm being lazy and dont want to dig up and run the numbers on the thermodynamics of the stock cooler and its cooling potential with a certain amount of flow of x degree fluid through it so I can't say for sure that it will or won't experience this phenomenon but it may.

Yes the stock cooler is a fine set up, more than most trucks have. However I am a proponent of having my transmission run on the cooler side rather than the hotter side, I'd still put an additional tube and fin or better yet a Bar and Plate cooler in. Judging by some of the temps I've seen people reach on the site I would safely say that an additional cooler would be a good idea.

The factory cooler is well setup to take the load, have you looked at it? It's huge in comparison to most aftermarket coolers.

Meh, its a good design and a decent size. I certainly wouldn't say its huge in comparison to most aftermarket coolers though. The problem is the trans fluid also goes through a pre-heater in the radiator to aid in cold weather start ups (gets the trans up to temp faster) so if you are running up a hill heating up your trans fluid and coolant then effectively the only trans cooler you have is the small on infront of the radiator. In this case it is actually undersized.

@Whileemptyheadsdream name is Reed bud, I hate my username. I was getting frustrated because the mud reg rejected my attempts for like 20 mins.

If your son is set on towing with his 80 I'd recommend a coolant temp gauge (the stock one doesn't show enough detail nor real time temps) and a trans temp gauge on the outgoing hose and also an additional trans cooler.

I'd put a red thin piece of tape at the 220 mark on the trans and tell him he should not exceed that temp, maybe 240 on the coolant temp... IDK whats too hot on the coolant maybe someone else can chime in there. Hope these post help.

 

[Mighty690]

Define "long time", if the grade is say, 6 miles long and you are going 60mph, that is ~6min, is that "long time"?



At least on mine, if the throttle is matted on a steep grade the trans will drop to 2nd, it's in the factory programing. Depending on grade, it will sometimes hunt between 2nd and 3rd, so I hold it in 2nd int gear that I prefer with the shifter.

My guess; the manual is written for the world market, all of the USA market rigs came with a very nice/large cooler, not true of other markets. On USA market rigs, I have never seen anything temp wise that I would consider concerning, and we go uphill often in desert conditions.

Tools,
Thanks for your thoughts. I'm impressed to hear how hard your rig runs and takes it. I ought to give mine more of the beans!
I agree about holding it in 2nd when it's hunting, which makes total sense to me, but that Manual got me to questioning myself.