Team,


Recently, I noticed a sudden drop in MPG (I watch closely and have a very consistent commute and load with no stop and go driving so little variation in tank to tank MPG). As I tried things to find the root cause (changed the oil, cleaned the air filter, checked tire pressure, etc), I notice that it seemed my transmission temp took forever to get up to a stead state.


Now this its spring here in the south, I would expect the tranny to get up to full temp during my daily commute (50 miles at 60 mph each way). What I am seeing is a max temp of ~150 deg with an engine oil temp of 193 deg on a 70F day.


My questions are 1) what should be the normal operating temp for the tranny during light load, steady state operation (closer to engine oil, I would assume)


2) How long in mild weather should it take to reach steady temp (engine oil gets to 193 in approx. 15 miles while the tranny takes 40+)


3) does the transmission oil cooler have a bypass or thermostat that could have gone bad and would this contribute to a loss of MPG (I assume it could due to increased viscosity of the transmission fluid)


I appreciate the thoughts and help of the experts.

 

If the 6 speed TS is the same as the 5 speed, it has a 170 degree t-stat bypass in it. Perhaps Mark Kovalsky will happen along and elaborate. He's a former Ford tranny guru.

 

What are you using to monitor the trans temp?

 

I am just using the gauge view within the dash display. I have TorquePro but I have just been using the truck display since I figure its close enough for my purposes right now.

 

I Wouldn't rely on the factory gauge for minor temp. Changes. They are good for gosh and by golly monitoring.

 

Is that the digital one on the productivity screen?

 

The one he is talking about is exact. In the center info screen it shows the temp.

 

I never worked on the six speed TorqShift. I left Ford about that time.

I've heard, but not confirmed, that the internal thermostat is about 195F where the five speed was 165F.

 

Can't really contribute anything other than what mine does. It generally takes about 10-15 miles at highway speeds to get tranny up to operating temperature, around 195* with ambient temps around 70*

 

I need to check the digital screen from tranny temps and get back to you as I am pretty much always in the cold. The truck takes a long time to warm up - period. In the sub zero temps on the highway I can get the needles to go back all the way to cold if I am going highway speeds to the point that heater quits blowing out hot air. Even though the Ford manual says no winter front is needed... And I can tell you that cold makes you take a hit on MPG.

 

99150 - thanks. That is kind of what I would have expected. As I watch my tranny temp over the 50 miles I drive each way it continues to rise over time, but never plateau. Unlike a cooler which has a thermostat which would reach operating temp and then bounce up and down a few degrees.


Everyone's comments make think I have a thermostat or bypass that is stuck open causing the fluid to constantly cycle through the cooler.


Thanks for the help. I have 125k miles so I might as well get this looked at and flush the transmission at the same time (I think they recommend 150k miles)

 

Mine sits at 195 all day long once at operating temp. But I don't understand they'd run them at a higher operating temp. More heat is good now?

 

My '11 F350 would hit 195 within 50 miles, even in cool weather. Sounds to me like you have a thermostat problem.

As I understand it, warmer fluid is thinner, which contributes to less pumping losses in the transmission. It's more efficient. Mark has said in the past the older gen transmissions could run 225 all day, every day and never suffer a shorter lifespan or heat-related issue. The 6R80 in my F150 runs about the same temperature.

 

Keep in mind the trans cooler has coolant cycling through it at 140F. I personally cannot find anything suggesting there is a transmission thermostat in the 6R140 between it and the cooler, but others seem to think there is.

The transmission definitely takes much longer than engine oil to warm up, and on very cold days, mine will never reach 190+ degrees. But I'm talking like highs in the single digits and less.

On a 30-degree day, Mine will reach 190F and sometimes as high as 203F after traveling up a long hill at 70mph with the cruise on, empty.

I think based upon your drive length, it should reach 190+ degrees.

On a side note, I was stunned how much my fuel economy improved immediately after the first oil change. I had a 35 minute run up the highway to the nearest dealer, so I reset the economy on the way up, and then from the dealer back. I honestly saw a 4 mpg difference. The dealer said they also "checked tire pressures" but I'm assuming they were fine previously. Perhaps the terrain was slightly more downhill on the return trip, but I was impressed. I'm assuming the slipperiness of the new oil gave me the improvement.

 

Um....no. That's not how this works. There are all kinds of reasons for a fuel economy change, but "slipperier" oil just isn't one of them.