I was on my way to work this morning in 8-10 degree weather. I happened to notice my trans temp was several degrees higher than normal. I’ve only seen it go above 162 degrees when towing in warm weather. Well, after about an hour of driving in the cold at about 70mph it was up at 167-168, which makes no sense to me. Especially since my coolant and oil temps were lower than normal. Then all of a sudden it was like a thermostat opened in the trans and the temp went down to 155, then slowly climbed back to its regular 162.

Is this normal? From what I understand the trans cooler line only opens up when the trans temp gets above 170 (or thereabout), but I’m curious as to why my trans fluid would get hotter in the cold weather.

 

So, on the way home in 26-27 degree weather the trans temp was 158. I guess it’s possible I read it wrong this morning, but I don’t think so. Guess I’ll watch it again tomorrow morning as the temps are supposed to be 9-10 again.

 

Maybe it took a bit more to open the valve since it doesn't open often?

 

How many are on your TP filter for the transmission ?

The transmission thermostat is not perfect temp wise either.

 

Could be...I’m just wondering why the temp was getting up that high in such low temps...

 

My trans. temps are higher when it is cold out. Below -20C. approx. 165. Below -30 approx. 175. It happens every winter. (new trans filter every engine oil change)

 

I changed out the TP filter and went to the 08 pan and filter less than 20k miles ago, fluid was clear red that I drained and put in 9 qts fresh fluid.

So possibly my trans thermostat is like the OEM engine stat and opening low, around 162. And maybe WatsonR is onto something, this morning maybe with the cold for some reason my stat needed a bit “extra” to open. Will check to see what it does tomorrow.

 

Huh...that is interesting. I wonder why that would be?

 

Thermostats are mechanical and use expansion of material like copper most often or chromium SS spring steel expansion and contraction for throttling and like me in the cold don't always move real well from it.
But the filter has thermostat and a bypass line that controls what sent to the cooler up front along with whats just returned to the transmission itself. If the toilet paper is running with additional restriction it will affect where the fluid flows as well as the temperatures in the transmission when more is bypassed back to transmission instead of the cooler up front.

In a nutshell if you see continued higher temps throw the toilet paper out for a new one. Don't forget to clean the floor too and remember to put the seat down.

 

External temp shouldn't really matter, it still should reach optimal temp, just take longer to get there... It started from a lower temp. It should open when it hits the right temp, 20° outside or 60°.

 

A thermostat opening is exactly what happened.

There is a thermostat in the transmission. It has a nominal temperature of 165°F to open. Nominal means it's an approximate temperature. Anywhere from about 155-175°F is acceptable.

When the thermostat is closed only a trickle of fluid is sent to the coolers. Almost all of the fluid just recirculates inside the transmission with no cooling. So that trans will warm to normal temps (and 168°F is perfect) in almost any temperature. That's how we designed it.

Why? Because the thermostat is not a digital device. It may open at 162°F one time and 168°F another time. Absolute precision on the opening temperature was not at all important, so no effort was made to make a thermostat that is 100% repeatable.

The thermostat in the 5R110W is a wax pellet, not a metallic. It's the same principle as an engine coolant thermostat.

The stock filter does not work like that. It does not have a thermostat in it. It receives 10% of the cooler line flow at any temperature that there is flow. 90% bypasses the filter. The filtered and non filter fluids are mixed back together and go through the cooler. There is no path for the filter to bypass the coolers.

 

Thanks, I was hoping you would reply!

I guess my only question is, would something cause the thermostat to consistently open at a higher temp when it’s really cold out? The last two mornings when I’ve gone to work it has been 8 or below (this morning -2) and on the way my trans temp gets up to 168 or so, then drops down to the regular 162. On my way home from work both days it has been 28-30, and the trans temp doesn’t get above 158 on the way home. Just seems odd to me

Could it be that the wax pellet (not sure how big it is...I’m guessing small) gets super cold and takes more time to heat up to let the thermostat open? Trans fluid temp was 13 when I started the truck this morning vs in the 30’s at startup for the way home.

 

Ive definitely learned THAT lesson. Mostly.

 

I agree, but hat seems odd to me is the trans is reaching a higher operating temp when it is super cold out, and when the temp outside is just cold it runs at a lower operating temp. -2 out this morning, trans goes up to 168 then drops to 162. 30 degrees outside on way home and trans doesn’t go over 158.

 

My trans temps do change with the thermostat opening and closing but end up at the temps that I posted. ( I only look at it when I am on the Hwy.) In the summer it is usually 145-150. What amazed me towing 6500# +2000 in the truck climbing steep grades through BC mountains (Hwy Thru Hell) is the harder I work the truck the cooler the trans temps are. I get that the fan is on hard but when the trans is only 135.F and the ECT is 220, EOT is 235 and the outside air temp is 90.F it tells me that Ford has done an excellent job with the trans cooling.