A few days ago, I was doing some data logging on my van. I noticed the trans fluid temp was warmer than I thought it should be. It is the much maligned Ford 6F35 with 109k miles on it. It has a thermostatically controlled valve that waits until the fluid is up to operating temp (about 180°F) before opening and allowing the fluid to circulate through the cooler. I saw it hit 208°F on a steady 75mph cruise after about 20 miles. I pulled into a fast food place to grab something to eat. They were packed and it took almost 20 minutes to get my order. I saw the fluid temp creep up to 230°F! Now, I lost the engine under cover due to a very inconveniently placed road gator (thrown retread). I noticed the bottom of the trans is covered in fluid. Upon closer inspection, the left CV axle shaft seal is weeping, which is a common 6F35 issue. I'm guessing the fluid level was pretty low but because Ford did not use a dipstick on this version of the 6F35, a guess is all I have. The trans does have a weird 2-3 upshift where it seems to shift at a higher RPM to 3rd than any other gear. The shift is a little harsh at times as well. I have also noticed a shift flare in 3rd sometimes too.
That scared me so today I went to the auto hobby shop to drain and refill the fluid. I bought a case of Mercon LV from Rockauto (came out to $5.12/quart including shipping which still beats the $8/quart at AdvanceZone). The drain and refill capacity is 4L (about 4.22 quarts). Here is what came out:
Yum! Now I know the 6F35 turns the Mercon LV dark pretty quick but the fluid didn't smell burnt. The pic doesn't capture it but it still had a little bit of a red tint to it. Ford says that you have to do the drain and refill 3 times since only about 40% of the fluid drains out each time. There is a plug by the driver's side CV axle that you remove and then fill up the trans until it dribbles out of that hole. The lift I was using was not perfectly level, with the front being a bit lower than the rear arms. I got 4 quarts of fresh Mercon LV before it started to run out the level hole. I quickly installed the plug then added another 1/4 quart. I made sure to run the trans though the gears for 5 seconds each while the engine was running to ensure no air was trapped in the passages.
On the way home, on the same 75mph, 20 mile stretch, the fluid stayed at 200°F before creeping up to 208°F as I pulled into my driveway. It would drop to about 203°F when I got stuck at a stoplight. According to the Ford FSM, normal operating temps for the 6F35 are 185-200°F.
What causes a transmission to get hot at a steady cruise? Lack of fluid which causes friction? Slippage? Why would the temp continue to climb when I was stopped? I just ordered a Sonnax ZIP Kit for it since its cheap compared to a valve body or reman transmission. I might have a sticky shift solenoid which isn't too bad to replace but I hope the clutches are still good.
Thoughts? Any powertrain engineers here?
The color in the pic might not show right, but that looks like the color trans fluid becomes when it has coolant in it. Put a sample in a clear bottle and see if it settles out some water/antifreeze after a day or two.
And stop looking a scan tool numbers. That sort of thinking is why they have gauges that lie to us now.
Transmission cooler clogged with bugs, grass and debris? Not enough transmission cooler?
In reply to Streetwiseguy :
Is it the cloudiness of the fluid you are talking about? You can kinda see in this pic that its still mostly clear but dark colored:
Its hard to take a pic while shielding your face from 200° trans fluid apparently.
And stop looking a scan tool numbers. That sort of thinking is why they have gauges that lie to us now.
But what if there isn't a gauge? Do I just do as Roadkill does? 
Brett_Murphy said:
Transmission cooler clogged with bugs, grass and debris? Not enough transmission cooler?
Hmmm. You know, I never checked that. It wouldn't surprise me if it was clogged with the corpses of a million love bugs. Also, the undertray is missing. Do you think that would make a difference? I have one on the way.
The 6F35 has an oil to water heat exchanger on top of the trans:
I wonder if the exchanger could be getting clogged? Or if I could replace it with a larger, front mounted trans cooler?
The sooner it fails, the sooner you have justifcation for a manual swap, anyway. 
In reply to slowbird :
I have been looking at how feasible it would be to swap a manual in. The 1st gen Transit Connect used a Focus drivetrain so manual swaps were super easy. The 2nd gen Transit Connect uses Focus, Fiesta, and Escape parts. Apparently the 2013+ Escape could be had with a 2.5L and 6 speed manual transmission. Since its basically the same platform, it *should* be a pretty straight forward swap. At least the mechanical part. I'm sure I'd have to grab the Escape ECU/PCM as well but I don't know how well the electronics would play with each other.
Or I could source the swap parts from Europe since they got manual Transit Connects right from the factory. Further research is needed .
Brett_Murphy said:
Transmission cooler clogged with bugs, grass and debris? Not enough transmission cooler?
Actually, coolant and trans fluid makes a literal strawberry quik looking mixture.
Hmmmm. I wonder if the heat exchanger is clogged with clutch material? If I go through all the trouble of pulling it off to inspect it, I'm just going to replace it since its about $60.
stanger_missle said:
The 6F35 has an oil to water heat exchanger on top of the trans:
I wonder if the exchanger could be getting clogged? Or if I could replace it with a larger, front mounted trans cooler?
If there is no front mounted transmission cooler, plumbing one in might not be a bad idea, provided that the fluid temp doesn't stay too low. Getting and OEM quality one from your local pull-it would probably cost $15.
Ranger50 said:
Brett_Murphy said:
Transmission cooler clogged with bugs, grass and debris? Not enough transmission cooler?
Actually, coolant and trans fluid makes a literal strawberry quik looking mixture.
I 100% agree, but that isn't what I was saying. I was saying that if he had a front mount, fin type cooler, the fins might be clogged with debris. I had a radiator that was otherwise fine start to fail at cooling because it was gunked up with mud, bugs and other schmutz. A good cleaning, straightening some fins and some compressed air and it was cooling fine again.
As it turns out, the transmission cooler he has doesn't seem subject to the vagaries of road debris getting stuck in the fins.
What was the engine coolant temp?
How different was the trans temp compared to the engine coolant temp?
If the heat exchanger is working I would expect the trans fluid and engine coolant to be pretty close in temp.
So if the engine temp was creeping up over 200 then the trans temp would follow, and possibly be higher than the engine temp
If the heat exchanger is clogged I would expect the trans temp to have a bigger delta from the engine coolant, indicating poor flow through the cooler.
stanger_missle said:
It has a thermostatically controlled valve that waits until the fluid is up to operating temp (about 180°F) before opening and allowing the fluid to circulate through the cooler.
I'm surprised no one has commented on this, even though it shows up on stanger's troubleshooting chart. I'd check for continuity or resistance against known values on this one.
Brett_Murphy said:
As it turns out, the transmission cooler he has doesn't seem subject to the vagaries of road debris getting stuck in the fins.
Thats OK, I didn't realize that there wasn't a traditional front mounted trans cooler on this van until I started digging into the transmission stuff today. All of the automatic transmission vehicles I have owned before had a trans cooler mounted up front which always got packed with leaves and crap. That is usually an easy fix though.
No Time said:
What was the engine coolant temp?
How different was the trans temp compared to the engine coolant temp?
If the heat exchanger is working I would expect the trans fluid and engine coolant to be pretty close in temp.
So if the engine temp was creeping up over 200 then the trans temp would follow, and possibly be higher than the engine temp
If the heat exchanger is clogged I would expect the trans temp to have a bigger delta from the engine coolant, indicating poor flow through the cooler.
Engine coolant temp was 191-196°F
Trans fluid temp was 200-210°F but spiked up to 230°F while sitting still for about 20 minutes. That high temp happened a few days ago before I drained and refilled the trans fluid. I have no idea how low the fluid was at that time.
The trans cooler is mounted on top of the transmission. The thermostatically controlled valve is mounted pretty close to the cooler. The exhaust is pretty close to the whole assembly. I'm sure its absorbing some radiant heat from the exhaust.
When I owned a 6.0L Powerstroke, the oil coolers were a big issue on those. If I remember correctly, the temp delta between the water and oil temps was supposed to be 15° or less. Any higher and it was a sure sign that the oil cooler was plugged and bad things were going to happen if you didn't replace it ASAP.
Jerry From LA said:
stanger_missle said:
It has a thermostatically controlled valve that waits until the fluid is up to operating temp (about 180°F) before opening and allowing the fluid to circulate through the cooler.
I'm surprised no one has commented on this, even though it shows up on stanger's troubleshooting chart. I'd check for continuity or resistance against known values on this one.
I have heard of people removing the valve all together. My unscientific guess is that the valve allows the fluid to come up to operating temp quicker for gas mileage and emissions reasons. Cold and highly viscous transmission fluid isn't a big issue here in Florida haha.
But you do bring up a good point. If the valve is stuck closed, then the fluid wouldn't reach the trans cooler. Kind of like when a thermostat fails closed. I'll see if I can find some diagnostic information on it.
In reply to stanger_missle :
That eliminates the possibility that it was higher than normal engine temps causing the trans fluid to read high.
Higher temps when sitting compared to highway still seem reasonable. The torque converters going to generate more heat unlocked than locked, and the water flow rate is lower it idle than 65mph.
How do the temps compare to previous data logging?
You could try using an IR temp gun to check the line temp on the inlet and outlet to see if fluid is flowing. No flow will affect the line temp and delta between inlet and outlet.
