Auto Trans Altitude OD Switch

[MightyMontana]

I apologize for this old thread, but I can't seem to find what I need with the search function, all in one place.

I have 1986 22re Sunrader Auto Transmission Altitude Sensor Switch Questions

I understand the purpose and function of the switch as it normally functions. What I need answers and possibly pictures of are as follows.

Where is the switch located? Where on the transmission body? I thought I saw a picture somewhere but can't find it again.

Was it installed by the Sunrader Corp? Toyota Dealerships have no idea what or where it is and have no part number etc. Some deny it exists. Can it still be ordered if it fails? What part number and who made or makes it?

Can it be calibrated so it doesn't cut out OD at about 3100 ft? I would like to be in control.

What "switch" is located under the dash above and behind the brake pedal that you can splice a manual switch to to control the altitude switch or some other OD function?

What is the proceedure to install a manual switch to let you control (deactivate the altitude switch) when the OD comes on and off? I find the link but there seems to be no detailed instructions.

Any help will be greatly appreciated as I live in he mountains of western Montana and need more control and hope there is a way to work around the switch to obtain manual control.

Thanks in advance for any help and answers to my questions needs.

[Derek up North]

The altitude (Pressure) sensor might be located behind the dash (near the speedo) or behind the driver's side kick panel. I've seen both reported.

[WME]

Why bother. The standard recommendation is to never use OD.

WME

From high in the Rockies in Wy.

[Lee & Joan]

I like WME had heard not to use OD, but my recent trip over the same roads & conditions I switched it back on. My MPG went up about 2 MPG. So now I am also interested in being able to selectively activate OD over 3000 feet. Long downgrades come to mind as the place you would want to reactivate 4th gear.

[cabinguy]

The relay is mounted on what would be the clutch pivot, under dash, it is marked as such, simply unplug it, run a jumper wire between the top 2 female connections with a switch in line, and you now can select to use overdrive, anytime even over the 4k limit that is factory.

Did this to an 86 dolphin, though the trans and set up should be the same no matter what the actual camper manufacture is.

[noahrexion]

Toyota Part # 89531-28010 is the relay, it is blue and has 3 wires running to it (all are female) and two are in line with one another - I believe these are the two wires that 'cabinguy' is referring to.

I, too, would like to try this and will be taking a stab at it soon enough. Please let me know how this works out for you. I asked this exact question either here or on Yahoo boards and received no direct answer.

Thanks for the help cabin guy. For reference this is on my 86' Dolphin. Please report back if you try this out Montana!

[Bob C]

Hearing about this altitude sensor switch is very good for me. i am going to the Rockies next summer and would have tought that the RV tranny was going to die because it would not go into OD while coasting down gradual grades. I always use the tranny for engine braking in the hills of SW WI. My Dad was a truck driver and ALWAYS told me to go down every hill in the same gear I went up or one gear lower. My Toy has a overdrive deactivation button on the end of the shift lever, would it still have the pressure switch?

I have pulled trailers all over the country and have never made the brakes hot, not once. I plan on doing the same with the Toy.

[Maineah]

The cut out is more for the engine then the trans you lose a good bit of power at altitude that's why they lock it out but it an easy thing to do with the button on the shifter, to my line of thinking is it's good for both. I can see where it would be an issue if you live in the hills and are not going up and down them.

[waiter]

Bob;

Never go down a hill any faster than you went up the hill - Sounds like we have the same philosophy.

Trust me - This will NOT be a problem in the Toyhouse.

I've found I rarely need to use the brakes on anything but the steepest of grades (10 - 15%). The aerodynamic frontal area of a Toyhouse is about equivalent to that of a barn door, and, although they are heavy, 6,500 lbs, it won't build up speed on those downhills like an 80,000 lb 18 wheeler.

I haven't bypassed my altitude switch yet (its on the list, and most of my driving is low land), I just haven't found enough circumstances where I've found myself saying; "Darn, I wish I could put it in OD". In fact, unless I'm drive 55 on the flats and have a tailwind, I normally don't use the OD.

John Mc

88 Dolphin 4 Auto

[Bob C]

My Dad would kick my butt if he heard that I was going fast on a downhill. I was pulling a 2500 lb pop-up behind my Chevy Caprice coming out of the Bighorn Mtns headed toward Cody WY and never heated the brakes. I ended up going down in secon gear and occassionally had to go to first due to the drop. In first gear I had no problem keeping the speed down around 25. I pulled into a service station in Cody to fill with gas and the mechanic came out to the pump and told me what the price was for a brake job. I told him that I never heated the brakes up and he did not believe it. That guy is getting rich because people never learned how to downshift.

My daughter was taking drivers education and the instructor told her not to downshift on the hills. She informed him that her dad told her how to properly drive in hills and that if the instructor wanted to argue, argue with dad. The guy called me and I asked him if he ever drove a truck. He informed me that he had not. After a little discussion, he agreed to leave my daughter alone about it. the next year, the same daughter was driving down a very steep grade pulling the 2500 lb trailer and the brand new brakes on my Chevy Astro blew a line (improperly installed by the dealer.) She just kept downshifting and got around the corner at the bottom. She was sure glad that she learned to use the tranny.

[McShank]

I finally got around to bypassing my altitude switch and replacing it with a dash mounted toggle. At the same time I installed a vacuum gauge to help me know when I should downshift from whatever gear I'm in. I spend a lot of camping time at higher altitude and the noise of the high rpm's even when I'm just going downhill was so very loud we couldn't hear each other. (Insert marriage jokes here - we just celebrated 22 yrs.) With my 4 cylinder engine the vacuum gauge spends most of its time in the bad zone but it still tells me when I am leadfooting with no benefit.

Seamus McShank

[86rader]

Excellent post, McShank. I think you are dealing with the OD situation the smart way. Unnecessarily spinning at high revs on downhill grades is silly, IMO. Staying out of OD completely may be the right solution for those unsure about what gear they should be in or simply not willing to be bothered with it and that is fine. Personally, I enjoy being part of the decision making process.

The drive downhill in the same gear you drove uphill may make sense in some vehicles, particularly vehicles with better power to weight ratios that can climb at decent speeds. But as has been mentioned, the toyhouse has a built in parachute and will roll down slight grades safely in OD with little or no braking. These same grades can not be climbed in OD if you tried. It all comes down to using good judgement. If you are on the brakes much at all to keep a safe speed, you really do need to think about going to a lower gear before you smell brakes.

I have a few other questions concerning this.

Does fuel shutoff completely with the V-6 during engine braking? I know it does with modern engines. I doubt it does with the 22RE. If you lived in an area where you regularly drove down very long downgrades, installing a FI cutout switch might make sense. Then again, it might also result in you blowing something up with the ECU! So, maybe it's a bad idea. Also, I guess it might result in stalling an automatic which would make it a very, very, very bad idea.

Please disregard the last paragraph!

One other question regarding vacuum gauges. I realize that the higher the vacuum, the better, with a carbureted engine. I am not so sure that this is the case with FI. Remember that FI engines have O2 sensor(s) which keep the fuel air ratio about right. Carbed engines don't and fuel air ratios get out of whack under heavy load.

[Bob C]

Long stead grades are not my problem here in Wisconsin's hills. We have short steep hills with corners all over them. Last weekend I ended up in second gear on the way down to make the 30 mph corner at the half-way point. We may only loose 600 feet in elevation but it will happen in about 3/4 mile but there may be a couple of 45 degree curves thrown in to keep us awake.

[stacy]

MightyMontana - I just bought an 86 sunder and brought it back to taos, nm where I live (7500 ft) and am wanting like you to find out more details about the o/d bypass. It is in the shop now and the mechanic is also wanting to know more actual details about 'how' to do this process. Did you ever find out anything specific to this post as to how or did you figure it out yourself? Any help on this would be greatly appreciated!!

[douglitas]

yeah getting ready to do this too! any pointers about exactly how to bypass the elevation sensor for OD? mine is '87 Seabreeze 4 banger with auto trans.

thanks!

[straygoose]

Why bother. The standard recommendation is to never use OD.

WME

From high in the Rockies in Wy.

Why is that? I use my OD all the time, unless it's an extreme climb. And with rolling hills and such, as soon as you step on the gas it kicks out of OD and into "passing" gear.

I'm glad mine has OD. She runs at pretty high rpms without it. Don't have a tach, but just by the sound of her I'm guessing over 3000rpm at 55mph. She doesn't nearly run that hard in OD.

I just wish I had cruise control on mine. It is the only thing I don't like about my GranVille. Anyone know where to get cruise control installed. I checked around a couple places in my travels and they just looked at me kinda funny. no one seems to install after-market CC anymore.

[waiter]

If you get the Cruise Control, make sure it has an electric servo (The thing that moves the gas pedal). Most cheap aftermarket use a vacuum servo. Problem is, your gas pedal is on the floor a lot and you don't generate a lot of vacuum.

John Mc

88 Dolphin 4 Auto

[WME]

Why is that? I use my OD all the time, unless it's an extreme climb. And with rolling hills and such, as soon as you step on the gas it kicks out of OD and into "passing" gear.

I'm glad mine has OD. She runs at pretty high rpms without it. Don't have a tach, but just by the sound of her I'm guessing over 3000rpm at 55mph. She doesn't nearly run that hard in OD.

I just wish I had cruise control on mine. It is the only thing I don't like about my GranVille. Anyone know where to get cruise control installed. I checked around a couple places in my travels and they just looked at me kinda funny. no one seems to install after-market CC anymore.

Do you have a temp gauge??? Lots of heat in OD. Lots of toasted transmissions in the Toyota forums.

WME

WME

[straygoose]

Do you have a temp gauge??? Lots of heat in OD. Lots of toasted transmissions in the Toyota forums.WMEWME

I assume you are talking about trans temp, and no I don't have gauge for that. I do notice that engine temp goes up a bit on the long climbs, but other than that, no problems. I shut the OD down when I'm climbing hard anyway.

[zero]

I find it hard to believe using OD causes excessively high heat when used properly. Since the RVs have conventional torque converters, they slip ALL the time regardless if in OD or not. Slippage causes heat and coolers are there to deal with it. The standard figure for normal torque converter slippage at highway speed on a flat road is 15%. If you engage OD and the RV does not seem to be working extra hard - I doubt it hurts anything. Now if you're climbing hills in OD and putting the gas pedal to the floor and "lugging" - well yeah. Then slippage will increase and so will the heat.

I hear lots of stories about people frying transmissions. But -most that I've heard are from people who have never rebuilt a transmission themselves and often do not know what condition the trans was in before it blew. After a rebuild I'm sure many people never know for sure what caused the failure. I do know, for sure that many transmission repair people are blatant liars.

Any transmission - manual or automatic is stronger in direct-drive (no gears used) then when in OD. Not because of the heat. More because extra gears, brakes, bands, sprag-cluthes, etc. are in use. The main thing is if the trans OD is built heavy enough for the GVW.

I've got a 20 foot Minicruiser with the A43D trans (no lock-up) and 22REC engine. It drives much nicer and quiter in OD when I'm on a flat highway. If I come to any substantial grade and it really starts to slow down - I just shut the OD off. At least on my rig the OD makes a big and nice difference.

I will say though that from fuel mileage tests I've seen, the OD does not increase MPGs. That struck me as odd until I looked at Toyota engine specs for 22R engines. They have a very high RPM peak torque curve. So, they can get optimal fuel mileage at higher RPMs then many other engines.

Any engine makes it's best MPGs when run at its peak torque curve. My diesel trucks (Ford, GM and Dodge) all have peak torque curves at 1800-2200 RPM. The Toyota 22R peaks at around 2800 RPM.

[linda s]

Well there are too many people on this group and others who have measured the difference in heat with OD on or off. Addition of tranny temp guages is pretty common with toyota motorhome owners and many have relayed their results. Much higher heat build up in the tranny with OD on. No I don't think they all made it up. Many are experienced mechanics. I do get better mileage without OD so it has never been an issue for me. Why would I push that button and lose mileage. I am talking about the 4 banger only.The v6 has no known issues as far as I know with OD

Linda S

[zero]

Well there are too many people on this group and others who have measured the difference in heat with OD on or off. . Much higher heat build up in the tranny with OD on. No I don't think they all made it up. Many are experienced mechanics. I do get better mileage without OD so it has never been an issue for me. Why would I push that button and lose mileage. I am talking about the 4 banger only.The v6 has no known issues as far as I know with OD

Linda S

That sounds like a broad, anecdotal claim with no hard data to back it up. Claiming that "everone on the Web says so{" does not make it so. I haven't heard nor seen a single post with actual conditions given, and what parts actually failed. Linda - by your claim, you are also saying that Toyota made a huge goof offering the A43D in 1 ton trucks? They did it for years and sold many HD 1 ton chassis-only trucks they knew were destined to be RVs or box trucks. I guess the Toyota engineers are less informed then the Web-posters you speak of.

For this "danger-high-heat" story to make credible sense - seems we need some case histories with #1 a transmission known to be in good shape at the start, #2 how it was used in OD including ambient temps, GVW, and angle of inclines climbed, #3 normal temp verus OD temp under flat, medium and steep grade use, #4 if a trans failed a detailed report on exactly what part or parts failed, etc. Most transmission fluids can sustain heat up to 380 degrees F. Clutches and seals can withstand 300 degrees F. So what is going on here? The Toyota engineers don't know what they're doing? People are hitting the OD button and having their transmissions climbing over 300 degrees F? I'll add I guess these same people have large oil-to-air coolers that can't fail to keep the temp down?

You ask "why would anyone push a button to lose mileage?" I know a few people, including me, like the quieter engine when on a long flat stretch of highway that the OD provides. I suspect any fuel mileage loss is minimal but cannot say I've done any well-controlled scientific studies on the subject. I've seen published road-tests for these RVs in and out of OD but I don't know how they were actually being driven. Using OD is going to cause loss and excess heat if the RV is lugged. If not - I doubt it hurts a thing.

Back to the apparently clueless engineers at Toyota . . . one would think if using OD caused such a heat hazard . . . the 1 ton trucks would have trans-heat-temp-sensors that would block out OD when temps got to certain level. If they did it for high altitude, they could of done it for heat for just a few extra bucks.

[Gulfstream Greg]

Why bother. The standard recommendation is to never use OD.

WME

From high in the Rockies in Wy.

I agree but only as far as the 4cyl is concerned. The V6 and Turbo 4cyl all use a trans with a locking torque converter, the standard 4cyl carb and FI do not. The constant slipping in the 4cyl converters is what generates the heat. OD just makes it worse.

Also I thought that I read somewhere the altitude sensor was adjustable.

[zero]

I agree but only as far as the 4cyl is concerned. The V6 and Turbo 4cyl all use a trans with a locking torque converter, the standard 4cyl carb and FI do not. The constant slipping in the 4cyl converters is what generates the heat. OD just makes it worse.

Also I thought that I read somewhere the altitude sensor was adjustable.

If the "standard" recommendation (whatever that means) is never to use OD - why do you suppose Toyota included it when they built 1 ton trucks with the A43D and the 2.4 engines?

[linda s]

Well Toyota must have known people were having issues with the tranny's because they started adding an extra tranny cooler in 1987. What you keep calling anecdotal is the reports of dozens of very experienced toyota motorhome owners over many years. People who have actually recorded their results instead of just guessing like you seem to be doing.

Linda S

[Derek up North]

Do you suppose Toyota would build a 'niche' A43 transmission for the MH market without overdrive? Somehow I doubt it. They made one to try suit everything from an empty flatbed to an overloaded MH. The Owners Manual (1992) does have a note not to use overdrive while towing to help with engine braking. Not sure what's written in other years.

If we agree that: "Any engine makes it's best MPGs when run at its peak torque curve. ... The Toyota 22R peaks at around 2800 RPM." then 55mph NOT in O/D is a fair bit closer to 2800rpm than 55mph in O/D. "Ya pays yer money and takes yer choice."

http://pw1.netcom.com/~sgalaba/mph.htm

[straygoose]

Sorry to start a dustup, but I'm still not completely understanding this. I have automatic OD. That means that when I am going up a hill, if I step on the gas hard, it shifts out of OD and into the "passing" gear. If necessariy, it will even shift into another "climbing" gear on long, hard hills. I try to avoid that, since I figure the engine is running close to red-line at that point.

I'm not trying to prolong the argument here, just trying to figure out what you guys are trying to say. It sounds to me like you have OD, but its not automatic, which doesn't make sense. Or that driving with OD and the cruise control on at the same time is the problem. That would kind of make sense since I could see the CC overriding the OD, causing the trans to overheat because it didn't shift out of OD.

My Goose is an '87, but its on an '86 chassis. Was the powertain package for the '86 Hilux any different from previous or future model years? I know I have this funky 1/2-ton front axle, 1-ton rear setup, but other than that I thought she was pretty much a generic Toyota setup.

BTW, I had the trans flushed and tuned about a thousand miles ago (43K), and I asked the trans guy if anything looked amiss. He said that the old fluid looked great and that the internals looked great. I did specifically ask him if the trans fluid showed any signs of being burnt (the smell test), and he said no.

So, I don't be seem to be having this problem of the OD overheating the trans. And I drive her virtually every day, to the tune of 14K+ miles since last November, probably 80% or more of those miles in OD. Maybe the previous owner put a trans cooler on her and I failed to notice it. I'm going to have to check on that, and if not, she's going to get one soon as I get home next month.

Either way, I'll keep an eye on my trans fluid. It'll be the first indicator of any overheating problems.

To Linda:

How do you get better mileage when you constantly run at higher rpms? I tried running without the OD for a full 200 miles a few times and went through way more fuel than when in OD. Matter of fact, one time I don't think I even made it 200 before having to re-fuel. And I usually get 220 or more if I'm topped off, on mostly flat highways or rolling hills.

Not saying your wrong, but if you are pulling it off, I want to know how. Could be useful information down the road somewheres.

I drive a lot of miles in my RVs (anywhere between 15-20K miles a year). I've had the Goose long enough now that I know her fuel needs like the back of my hand. She gets waaay better mileage running in OD.

[waiter]

Make sure you have an aux tranny cooler, looks like a mini radiator just in front of the engine radiator. These trannys run hot and need to be cooled. The heat generated seems to be the culprit for the early demise of the tail shaft bearing. (If you don't have one, I'd recommend one, cheap and easy to install)

The OD is automatic, its like a 4th gear, and behaves just as you described. It will upshift / downshift automatically as torque is required (throttle setting vs speed)

It can be disabled if the popping in and out get to a nuisance. It will also be automatically disabled if your vehicle is above 3000 ft in altitude.

There is ongoing discussion on does the OD really save gas? I would say from my 25,000 miles that it appears to not save fuel, and may actually cost a tiny, tiny bit. HOWEVER, I have not taken any real accurate data to support that conclusion. It just seems to be that way. I also throw in that same mix, I have Cruise Control, and its possible the that could be aggrivating the fuel MPG, as the CC may be constantly "hunting" the throttle,m where a nice constant pressure would be much better for fuel economy.

I'll work on this later.

JOhn Mc

'88 Dolphin 4 Auto

[Gulfstream Greg]

If the "standard" recommendation (whatever that means) is never to use OD - why do you suppose Toyota included it when they built 1 ton trucks with the A43D and the 2.4 engines?

The standard recommendation was originally conceived from/by 4cyl owners that assumed the V6 was the same animal as far as the trans is concerned. It was born from trans over heating issues and the fact that the 4cyl (even the FI engine) was under powered to run in OD with a grossly over weight coach and cargo strapped to its back. The altitude switch falls into the same arena. Even an empty 4cyl fi engine pickup at altitude is under powered and cannot support OD properly. The altitude switch was engineered in for a reason. Maybe fuel mileage, emissions, engine damage or all of the above. Urban myth has it that lugging an engine is one of the worst things as far as prematurely wearing out the cyl walls, cam and crank of an engine. Wonder if the myth busters ever covered that one? Maybe Toyota knows more than we think we do.

[straygoose]

Make sure you have an aux tranny cooler, looks like a mini radiator just in front of the engine radiator. These trannys run hot and need to be cooled. The heat generated seems to be the culprit for the early demise of the tail shaft bearing. (If you don't have one, I'd recommend one, cheap and easy to install)

The OD is automatic, its like a 4th gear, and behaves just as you described. It will upshift / downshift automatically as torque is required (throttle setting vs speed)

It can be disabled if the popping in and out get to a nuisance. It will also be automatically disabled if your vehicle is above 3000 ft in altitude.

There is ongoing discussion on does the OD really save gas? I would say from my 25,000 miles that it appears to not save fuel, and may actually cost a tiny, tiny bit. HOWEVER, I have not taken any real accurate data to support that conclusion. It just seems to be that way. I also throw in that same mix, I have Cruise Control, and its possible the that could be aggrivating the fuel MPG, as the CC may be constantly "hunting" the throttle,m where a nice constant pressure would be much better for fuel economy.

I'll work on this later.

JOhn Mc

'88 Dolphin 4 Auto

I figure it probably does have the cooler already, and if not it will get one when I get back to Texas. Like I said, the mechanic that did the flush said everything was fine, so I suspect I don't have the overheating problem. I'm going to take a look for the cooler later this afternoon.

Yep My OD is the same. I have the on-off switch on the shifter lever, and a little orange light by the AC console.

I'm still don't get the OD hurting the mpg angle. I get better mileage with OD on and running at lower rpms. I understand the power band theory, but I still get better mileage with OD. I drive a lot of flatlands and gently rolling hills, so that might be the reason. I rarely have to boot her in the rear end with that passing gear to do any climbing.

I took her through the Appalachians on her maiden trip with me and found out right away that her and the mountains are not a good match. So now when I head back down to Texas I just go around 'em. The trip is like fifty miles longer, so its no big deal.

And I certainly didn't make a huge study of it. I just know from experimenting on a couple of long trips that no OD=lower mpg. I have a pretty steady foot, so I'm reasonably sure its not my driving habits. It was probably about 1-2 mpg, by my reckoning. Maybe not as earth-shattering as I previously mentioned, but on some of the 1700 mile trips I make, 1-2 mpg means a fair amount of money at the pump.

Plus, I just have this aversion to running four-bangers at high revs. Blew a 4cyl. sky-high once and learned an expensive lesson.

[zero]

Do you suppose Toyota would build a 'niche' A43 transmission for the MH market without overdrive? Somehow I doubt it. They made one to try suit everything from an empty flatbed to an overloaded MH. The Owners Manual (1992) does have a note not to use overdrive while towing to help with engine braking. Not sure what's written in other years.

If we agree that: "Any engine makes it's best MPGs when run at its peak torque curve. ... The Toyota 22R peaks at around 2800 RPM." then 55mph NOT in O/D is a fair bit closer to 2800rpm than 55mph in O/D. "Ya pays yer money and takes yer choice."

http://pw1.netcom.com/~sgalaba/mph.htm

Toyota had the trans built by Aisin. For an extra $5 they could of included a temp-sensor that would prevent OD from working during high heat. NO new transmission design required. GM did it with many of their auto transmissions when in HD use. What many of you people are saying here is that Toyota screwed up for years and sold 1 ton vehicles with OD that could not be safely used? And they did it for years and never noticed? Sorry - but that sounds absurd to me.

Why do you suppose they added the altitude switch but no temp sensor to block out OD??

Peak "curve" for a 22R is 2400 to 2800 RPM. A Toyota RV with the 4.1 rear axle ratio and 185R-14C tires has RPMs as thus.

55 MPH

Four speed manual trans - 2960 RPM

A43D automatic 3rd -3400 RPM (15% slippage)

A43D automatic in 4th OD - 2450 RPM (20% slippage)

65 MPH

Four speed manual trans - 3500 RPM

A43D automatic in 3rd - 4025 RPM j(15% slippage)

A43D automatic in 4th OD - 2850 RPM (20% slippage)

[zero]

I'm still don't get the OD hurting the mpg angle. I get better mileage with OD on and running at lower rpms. I understand the power band theory, but I still get better mileage with OD. I drive a lot of flatlands and gently rolling hills, so that might be the reason. I rarely have to boot her in the rear end with that passing gear to do any climbing.

When Winnebago made their first Mini-Warrior Toyota with the four-cylinder 22R engine they published road-test results. They claimed 1-2 MPG better when not in OD - but - no mention was made of actual driving conditions for the entire test. That's the problem with published specs like that. Did they turn off the OD when climbing hills?? I don't know.

An engine makes its best efficiency when run within its torque curve which is 2400-2800 RPM for a 22R four-banger. But - other factors come in to play for MPGs. In some cases an engine run out of its torque curve gets better MPGs. The main issue is that cars and trucks get run an varying speeds and load. If an RV was being built to run at just one speed and a fixed angle grade - an engine could be sized to match it perfectly. In the real world, that so-far cannot be done. The closest anyone has come so far is with something like an Eco-Boost Ford engine. Basically and engine that "changes sizes" when load demands change. A turbo helps an engine act like one twice it's size only when needed - which is part of that tech.

No one is going to convince me - without some actual proof - that OD cannot offer a slight gain in MPGs when used in ideal conditions. If you use OD and cause the engine to work harder and you're pushing further on the gas pedal -fuel mileage will drop - as compared to the same speed in 3rd (1 to 1 ratio).

On the subject of RPMs? I like to see some specs from an accurate tachometer showing the difference of how much torque converter slippage occurs between 3rd (1 to 1 ratio) and 4th (OD 1 to .688 ratio). As far as I can tell - when driving down a relatively flat highway at 55 MPH - with my 1988 20 foot MiniCruiser -there's approx. a 5% increase in slippage in OD. 15% in 3rd and 18-20% in 4th. Not a huge difference. I did it on a windy day (off and on wind) so it was not a perfect test. Regardless of not having perfect accuracy - I refuse to believe the stories that the slight increase in slippage and heat destroys these transmissions. Of all the doom and gloom I hear - I'm still waiting for even one episode where accurate data is presented showing a clear cause-and-effect and exactly what specific parts failed.

It is obvious -at least to me - that Toyota could of easily put a temp sensor in the A43D trans to stop OD from working when hot if they were concerned. Maybe Toyota engineers don't read enough anecdotal stuff on Web-forums??

[Maineah]

Ok here is the deal all non-lockup converters slip fact of life. When you are cruzing down the road flat ground nice high way the engine is not making much horse power or torque no matter what the rpm and the slip is low. There is an optimal rpm for any engines power it is rated at X rpm what they don't tell you it is it’s at wide open throttle at X rpm. So just puttering along the slip is there but not bad because the power is low, greater than the average car due to the air drag but tolerable. The hills come into view and you have to put your foot down a bit HP and torque increases require gasoline not RPM and they climb rapidly with your foot on the gas now the slip really comes in because the power is there and the MH is not going any faster. Now would be the time to unlock the O/D. Yes they will down shift but at that point the HP and torque is really high and the convert is in full slip mode. I all ways used my O/D but it was the only thing I owned that was an automatic and I drove it like a stick and down shifted the O/D at the slightest hint of a load. Bottom line change the fluid every 30K add a cooler and lock out O/D when there is a noticeable load and the trans will make it 150K or more. And yes left to their own devices they will get hot.

[Maineah]

I was a manager for a very large transmission shop in MD we would not warranty overhauls on motor homes with out an added cooler most motor homes in the 80's just had the bone stock coolers they were not enough

[zero]

Adding an oil-to-air cooler makes sense for any car, truck, or RV if being worked hard. It can't hurt IF installed right with a thermostat that shuts out the added cooler in cool weather. The factory trans "coolers" that run through the radiators are also trans "heaters" for cold weather operation. The four-cylinder Toyota "box" trucks like U-Haul used had oil-to-air coolers on them.