Toyota WS vs Amsoil Fuel-Efficient Synthetic ATF

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Greetings,

I have a 2008 Sienna with a towing capacity of 3,500 lbs. I am towing a camping trailer that weighs 3,500 lbs and has the aerodynamics of a parachute
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Believe it or not, i get 35 mpg highway without the trailer and 15 mpg with the trailer....

I have installed one of the largest capacity ATF coolers I could find (21,000 BTU rating) and a Scangauge II to monitor the ATF temperature.

On a hot summer day (100 degrees Farenheit) after towing for several hours, the ATF is in the 200-210 degrees Farenheit range (and peaked at 222 degrees Farenheit). This is hotter than I would like.

I drain and fill (4 quarts) of ATF every 7,500 miles. In the next few weeks, I am going to drop and clean the pan, flush out all the ATF via the cooler lines and install a Magnefine filter.

My Sienna requires Toyota WS. I am considering switching out the Toyota WS for Amsoil Fuel-Efficient Synthetic ATF. My sole motivation is superior protection - I am not looking to save money. My layman's knowledge on this topic is that synthetic oils offer better protection - especially in a hot environment.

Any comments or suggests appreciated.

Thank you,
Gunter
 
You're concerned with temperature management; I'm curious as to how many gears are in your transmission, and if you are towing one or more gears below the top gear.

I ask this since if your trans is doing a lot of shifting between top gear and one below (like on every slight hill) it is generating a lot of heat and you are better off keeping it in a lower gear all the time.

The trans cooler will certainly help, but IMO 222 isn't all that high if you are using synthetic fluid. I'm a big fan of Amsoil and if their fluid meets the specs for your vehicle, then
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and I'd change it out.
 
One fluid has been tested by the vehicle manufacturer for the application, while the other has been tested by the additive supplier to be compatible in applications calling for WS. It is unclear whether the additive supplier tested their fluid in every single WS application on the market, whereas, you can be certain that Toyota did.

The choice should be fairly clear.
 
Why not contact Toyota of North America and ask them what they recommend as a ATF replacement interval with the data you have provided. If you are doing a drain and refill every 7.5K miles I would not mess with a complete fluid flush you are replacing fluid at a very frequent interval.
 
I used Redline D4 in place of WS in my Prius for 80,00 miles and it worked like a charm. If Amsoil says their ATF will suit it, then I believe it.
 
My Sienna has 5 gears.

When I am towing on flat terrain, I leave it in 4th gear. Once I get up to crusing speed (55 mph), the transmission does not shift at all. The engine is spinning at around 2,100 rpm.

When I am climbing a hill, I down shift to 3 or even 2 to keep the engine spinning around 2,500 - 3,000 rpm.

The combination of the above techniques seems keeps the # of shifts to a minimum.
 
you are going to kill it. Buy a 1/2 ton truck, even with a mid level engine and an economy gear it would tow fine. A van is for hauling people, not weighted shutes.
Toyota Tundra 4.7
Ford F150 3.7 V6/5.0 v8
Dodge Ram 4.7
Chevy 5.3
Even with gearing in the 2.xx-3.2x it would pull WAAAY better than the van.
It will be more stable and brake faster.
 
I talked to a guy that said he pulled a 32' bumper pull travel trailer ready to camp at 8,000lbs with his Sienna. He said it is a 10' and has 200k miles on it. I Called him on it and he had no proof..
 
If I had the $$$, I would happily upgrade to a 1/2 ton...

The Sienna, trailer, passengers and cargo come in under the GCVW. So, according to Toyota, the Sienna is designed to do it....

Surprisingly, the Sienna tows the trailer very well. The engine cooling temperature does not increase at all while towing. I also installed air bags in the rear suspension that keeps the Sienna perfectly level. The trailer has its own electrical brakes, so braking is not an issue. While towing, it feels very stable.

Over at the Siennachat forum, guys are pulling trailers heavier than mine and are not reporting any problems.

I realize I am putting a lot of strain on the vehicle. That is why I am looking for th best possible ATF.
 
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I would also install a magafine transmission filter. Possibly install electric fan on the cooler with a thermostat type switch. My vote goes to Amsoil assuming it meets the WS spec. Get some LT tires on the van to improve stability.. and for the love of god, don't be one of those rolling road blocks. it should do 65mph safely, if not something is amiss. I had to swerve around a Tacoma pulling a big TT. He pulled on the hwy from the merge ramp doing 40mph. I was going 65mph...the speed limit was 70mph. That was downright dangerous
 
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Personally, I would use Amsoil. Their base stocks are selected to handle the heat. I have used Amsoil ATF in most of my cars and trucks for many many years. Between its own weight, 5 people, gear, and a 6000 lb 24' boat; my van is pulling over 12,000 lbs in the summer, through the hills of Kentucky.

anyway; while you are certainly stressing your van - Toyota uses transmissions made by Aisin Warner. they are the best transmissions out there. period.
 
While you might be "maxed" at your trailer weight, you would also want to take a look at your GCWR (gross combined weight rating) and make sure you're not over that. While not a question you directly raised, it's important to note. That rating takes into account the vehicle weight, vehicle contents, trailer weight and trailer contents. As long as you're at or below the trailer tow rating and the GCWR, you should be fine. At face value, it seems you're OK. But it is for you to check and assure; I cannot diagnose it from here. Take your loaded rig to a scale and check to be sure.

As for the tranny fluid, you've added a nice sized cooler, and you're draining/filling probably way more often than needed. Your temps are not unexpected, and probably well within safe operating zones. If your tranny fluid got "hot" by Toyota limits, I suspect the CEL or other indicator would come on; if that has not happened, then you're fine. And with the added volume capacity and thermal effect of the cooler, I doubt you'd ever get to such a temp.

I'll add this because it applies indirectly to your concern of tranny temps:
The topic of wind resistance is often misunderstood. When you double your speed, the resistance from wind is squared! Going from 25mph to 50 mph is 2x the velocity increase, but the force requirement to overxome the air resistance might go from 30 pounds to 900 pounds of force! Therefore, small changes in speed on the highway result in a LARGE difference in force requirements. If you are traveling at 70mph, and drop even to 65mph, you can greatly reduce your force needed to pull the trailer. That force requirement reduction means far less stress on the tranny gears, and the fluid between them.

I once experienced this phenomenon in a "test" with my travel trailer in South Dakota heading out I-90. I ran 75mph for one tankful; the tranny temps were always over 200 degF. I dropped to 70mph on the next tankful and dropped 15 degF at the tranny temp, and gained almost 2 mpg in fuel efficiency. With only 5 mph difference!

Overall, the topic of ATF is really no different that engine oil or diff fluids. Often synthetics are not a requirement, but an option, based upon your intended OCI pattern. They may or may not make sense, depending upon your maintenance plan. There are plenty of good conventional products that likely would do well in your appliction.

So, I suspect you don't "need" an Amsoil ATF product, although you can certainly use one. Look up your vehicle on the Amsoil website, and get their specific fluid unique to your application; that way you're covered under their warranty. If Amsoil is your choice, please consider using our sponsor ... support those who support us!
 
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I use Amsoil ATF (ATL in your case) in every vehicle it's spec'ed for. That has included one Toyota, one Chevy, and two Chrysler. Never had an issue. Both in the transmission and transfer case. Toyota WS is obviously great stuff, but I feel Amsoil is better. A Magnefine filter is also a good suggestion.

What about the braking situation on the vehicle? Electric brakes in the trailer.

I think my Dodge Ram 2500 is the ideal tow vehicle for me. But my trailers are much heavier than yours.
 
My $0.02, I've owned I think 9 Toyotas over the years, although I don't have a Sienna...

I concur with others that you are pushing that Sienna to the max. Having said that, I don't think peak ATF temps of 222 is all that bad.

I also agree with use of Amsoil ATF. I'm using it in one of my Tundras, and will switch my other Tundra and my Camry to it when it comes time to change the ATF.
 
If you are concerned about temps, is is possible to put on a larger transmission cooler? Or put a small electric fan on the current cooler?
 
make sure you grab the proper Amsoil ATL... WS cars get the "low viscosity" variant IIRC.

The T&C in my sig stays around 180F-200F AT temps during the summer if the A/C is on and you're working it. Hill climbs and in-traffic performance moves will touch 210-220. I don't think your temps are too far out there, considering. Hway cruise is ~160F. It rarely breaks 125F in the winter.

FWIW I used to tow a 3000lb camper with a 3.3L chrysler T&C that was rated for 2500 lbs.. I never had a problem with it, and the longer wheelbase minivan far outdid the 97 pathfinder we later owned, that was rated for 5000lbs. When you say the sienna does it, I can absolutely believe it. Stability and control is far more important when towing than your ability to hold 60 mph up a steep hill.

The sienna is coil-sprung in the rear, which is probably a weakness. You've added helpers to make that better. Check for lightness of the steering wheel under firm braking. If the wheel gets light, consider using a weight-distributing hitch, if the receiver in the van will accept it. (if it's a class III it should).

The WD hitch, with a sway bar, basically forces the hitch to "roll forward" thus lifting the rear of the van and rolling it onto its front wheels. It is a HUGE improvement, especially on longer drives. The anti-sway bar is basically a sliding brake pad that resists L-R pivoting at the hitch, making the trailer less likely to "wag" and also improving cross-wind handling a good bit.

Tow safe! It sounds like you have a good handle on things. What brake controller are you using?
 
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