I have a 2004 F350 with the 6.0/automatic. I usually drive it about 18 miles one way and I plug in my block heater on both ends to keep it warm. (Even though it's not really that cold here) ECT/EOT runs about 185ish, my thermostat is weak. During this trip I don't usually see more than 145 for transmission temperature on my scangauge, and it takes the whole trip to get that high. It's usually not loaded much.

I'm wondering if this is too cool for the transmission? I know the filter doesn't see much action until at least 165, so mine doesn't ever do much. Is it normal for them to run that cool unloaded? I wonder if I could benefit from some sort of coolant/ATF heat exchanger?

 

That's pretty normal for mine and has been it's 200+K life.

 

I had to tow my 31' 5er in August to get into the 170 to 180 range. Yours is normal as Tim stated. The 6 speed trannys behind the 6.7 run around 200 normally.

 

I still wonder if it couldn't benefit from a coolant/ATF heat exchanger like most vehicles have? 145 doesn't seem warm enough to get rid of moisture very well. And it only hits that temp for a very short time. I wonder if MPG and shifting wouldn't be slightly improved from thinner (hotter) fluid viscosity?

 

Do you mean the transmission cooler in the radiator? Your truck left the factory with one of those. Did you remove it?

And it's a cooler, not a transmission warmer. It NEVER warms the ATF. It always cools it.

 

I didn't say it did. Obviously it doesn't. Coolant temp is around 185 and trans temp is 145. That still doesn't answer my question. In most other automatic transmissions they run a lot closer to the coolant temp. Wouldn't it be beneficial to run at least 165 since that's when the filter does the most work? And wouldn't it be better if the transmission was heated by the engine during warmup?

 

the last few day's I have been watching TFT 157 deg , on a long trip normal is 167/180 closer to 175 deg

 

Aha, that's warm, I have seen below 100 for long trips. It's running closed loop and until it's hotter for the thermostat to open to send to the cooler, it doesn't hurt a thing.

 

If I recall, the transmission is always sending around 10% of the fluid to the cooler. And the T-stat opens around 170*f.

 

I think that's correct and that 10% is also going thru the ext. filter.

 

F357: You might want to consider swapping out your trans pan and pick-up "filter" for the '08+ style. You get 100% filtration no matter what temp your trans is running. One of the reasons I did it is just that: they run cool, and the filter up front is a bypass style, so it sees about 10% of the flow, which means about 1% filtration all the while the trans is under 165ish in temp (where the thermostat opens to send more fluid up to the coolers).

About $100 in hard parts plus fluid (SP, LV you choose)...

 

You're both incorrect.

When the thermostat is closed 10% of the normal flow is going through the cooler. 10% of that flow goes through the filter. When the thermostat opens 100% of the trans fluid doesn't go through the coolers, just 100% of the normal cooler flow. That's more than half of the pump output, but not 100% of the pump output.

 

So if they bothered to put a 165 degree thermostat in it, somebody, somewhere must have decided it runs better at that temperature or higher, is that right?

Wouldn't we then benefit from a transmission HEATER in the coolant line?

Is there any particular reason this transmission runs cooler than almost any other automatic?

 

I guess I'd assume the opposite: They didn't feel the fluid needed to be cooled until it got to that 165-170 range...

Perhaps that is why they went to a full filtration filter? These trans do run nice and cool, that is for sure.

Maybe Mark knows why they went to the full filtration versus the bypass?

 

I tihink Dan is correct, the cooler and thermostat are there to protect from heat. There is no need to protect from colder temperatures or warm the transmission fluid. It is full synthetic and it works well below those temps, but it is not optimal for it to get too hot. The set point of the thermostat is set to protect against the higher temps, the cooler is designed to have capacity to cool when working hard and or in hotter ambient air temps. There is no need to heat the transmission. I have run my truck in -45 C weather for a day and the tranny temps never made it over 100 f. Doesn't hurt a thing, the tranny works fine. Without towing or load, there isn't that much heat generation. I think for any more extreme cold starting than this, a pan heater for both engine and tranny would be smart in addition to the block heater. This would be preferable to running the truck all night. Other than that, Mark K can confirm, as an engineer of these trannies, why its not necessary.