LV ATF thermal stability

[tundraman]

What is a good rule of thumb for sustained operating temps for the newer LV synthetic base ATFs? In earlier times, 220 F meant your transmission was on its way out. Now some vehicles run in that range continuously. I see a lot of the old charts of temp vs fluid life but if they are correct, there should be a lot of cooked trannys on the newer vehicles.
BC

 

[double vanos]

Mercon LV has a flashpoint of 421 degrees F. The transmissions that it is spec'd for I'm sure are designed to operate at much higher temps than the transmissions of yore.

 

[Fifty150]

What I hear, as common urban legend, is that modern automatic transmissions are fine operating between 200 - 225. But that all depends on who you ask.

Another thing to note is that temperatures vary depending on where you are taking the transmission fluid temperature.

Some install a sensor in the pan. Pan temperature is what a lot of people think of. Fluid is hotter inside of the torque converter and transmission. In theory, the cooled fluid in the return line is returned to the pan, where it is picked up and pumped back up into the torque converter and transmission, as hot fluid is sent out the cooling line.

Some use the vehicle's transmission temperature sensor. With a good OBD II connection, you can read what your car's computer is reading. Different people have different opinions as to where the sensor is located on a particular vehicle, and the value of taking the temperature from that specific location.

Some people install a sensor in the cooling line. This allows them to see how hot the fluid is as it exits the transmission to the cooling system. This temperature should be very high. It should be very high at that point. However, you have no idea what the pan temperature is. Nor do you know if your cooling system is working properly. You just know that you have hot fluid exiting the transmission, which even without a gauge, you should already know that it's really hot.

B&M, a company which sells transmissions & accessories, recommends taking the transmission fluid temperature at the return line. This allows you to know how cool the fluid is actually returning to the transmission, and allows you to monitor the efficiency of the cooling system. Sounds logical. Only problem is that nobody else subscribes to that theory. None of the OEMs take the return line temperature. And if your return line temperature is high, you are in a lot of trouble. That would mean that the fluid is extremely high before cooling, and that the cooling system cannot bring down the temperature.

 

[RoyFJ]

I have the FJ Cruiser and it didn't come with factory oil cooler. The transmission used is the robust Aisin 750 and it comes with Toyota WS ATF as factory fill and the dealer tells you its lifetime fill. Of course then fine print comes where it tells you to do a drain and fill every 60,000 miles if the vehicle is used under extreme conditions. This same transmission is also used in the overseas Toyota Prado, Toyota Tacoma as well as 4 Runner and other brands of vehicles. Except for some applications where a factory oil cooler is used, generally it doesn't come with one.
In my experience using a OBD scanner and Torque Pro the temps in tropical regions as well as summer regularly hits 90-100c or 194F in stop and go traffic and over 115-120C or 248F in slow hill climbs or off roading in sand even with 4 low. I have seen countless horror stories of transmission warning light coming on and frying the oil as well as many others with the infamous tranny shudder. Then there are others who have never changed their fluids and have their transmission running fine. In the end it all depends on where your vehicle is mostly driven and how its used but for me, anything over 90C makes me nervous as that also means higher torque converter temps as I have seen with my OBD scanner. This also means the friction modifier in the transmission oil will eventually break down and fry your TC clutch. I have no desire to face all that and have installed the Hayden 679 transmission cooler right after the radiator and now my temps even under extreme conditions never reach over 85C or 185F. I expect my tranny to last long with my 30000 mile drain and fill schedule. I would rather not pay for transmission service thats going to be prohibitively high and I don't expect good service where I live in first place.

 

[tundraman]

Since my new Tundra no longer has provision for a cooler, frequent fluid changes are the only option I have. A deep pan would be another option if not a warranty problem.
Thanks,
bc

 

[RoyFJ]

Also make it a habit to stay out of OD in traffic and hills.

 

[MolaKule]

The LV ATF's, while they have a fractional lower starting viscosity, will remain in grade at much higher temperatures.

And their low temperatures properties are superior as well with Brookfield viscosities well below 12,000 cp.

In addtion to viscosity stability, and also important, is the Friction Modification chemistry which is much more stable than earlier fluid versions.

Add to this improved multiple anti-oxidant chemistries and you have a much more stable ATF overall.

 

[RoyFJ]

I have always driven manuals so had no need to worry about transmission temps but the ML350 and my FJ Cruiser got me worried about coolers since they both don't come with a OEM one. MolaKule's article hit the spot and both got aftermarket oil coolers and I am a happy camper.

 

[zeng]

Transmission sump temperatures of 220F is a sure sign of impending transmission failures .
However 220F at torque converter outlet or inlet of cooler (as found in 'well equiped' transmisson system) is a different story altogether though.

 

[Fifty150]

Originally Posted by RoyFJ
got me worried about coolers since they both don't come with a OEM

Consider coolers with fans. The fans really work well.