10r80 custom thermostatic valve and cooler lines

[Rodpwnz]

Got under the car again today to check fluid level. Engine at idle, trans in park. I check dipstick and it's completely dry except for maybe a bit up high where it touched some fluid at the fill hole. Here is a picture:

Still the same dipstick reading after adding another quart of ULV fluid, totaling 7QTs. I was worried I would be overfilling since Ford and Haynes manual states 5-6 QT, but after researching more, I'm seeing 7.5-10QTs from other people online. I'll keep adding quarts of fluid and monitoring dipstick reading.

My trans was also making a whirring/humming sound that I don't remember hearing before dropping the pan. Might just be that fluid is low- here is a video of sound:

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[Rodpwnz]

I am now at a total of 10QTs in and still no fluid showing on dipstick with engine running, car in park. I get Fluid up to level 3 on the dipstick when engine is off. I only have 2 more QTs left and I'll be adding them tomorrow to see if I can get some to show on dipstick with engine running.

The pump whirring sound is gone now, I assume it was the fluid pick up pump inside transmission trying to suck fluid but level was too low.

 

[Rodpwnz]

I DID IT! 11QTS of fluid! Now fluid shows on disptick level 6 while engine idle + trans cold. Just as ford requires!

Ford procedure now states I can drive the car or brake torque(on and off 10 seconds) while in air to get trans to temp. Once at temp(200F+, 165F with my thermo), I will check fluid levels again and top up as needed.

I hope I didn’t cause any damage to trans by running engine and cycling through gear modes 5-10 seconds while super low on fluid….

I have one more QT of fluid remaining, and I think I will need it to fill empty trans lines and empty trans cooler. Maybe even another extra quart.

 

[GTP]

Way to go! It was exciting to follow your progress.

Keep in mind that trans issues can also come from too much fluid.

 

[Rodpwnz]

Way to go! It was exciting to follow your progress.

Keep in mind that trans issues can also come from too much fluid.

Thanks Philip, your projects were in part what inspired me to take on my own.

You're also right about overfilling, and that's why I've been so cautious about adding too much...so much so that I delayed adding enough!

Ford procedure calls for fluid to be at or below the 6 point on the dipstick when engine is running and fluid is cold. That is exactly where I am at now.

Once I get it up to temp(165F+ in my case), the thermostat will open up flow to Mishimoto trans cooler, which is roughly 1.5QT capacity(180% more than OEM cooler). I am assuming, once that is filled, I will need to add back another QT or so.

 

[GTP]

Thanks Rod. It's amazing how low it was.

 

[M5.0]

Awesome job, waiting for the good news!

 

[s197oldtimer]

Hi Everyone,

Project is complete and I've posted an update to original posting! Now all that is left is to see if I F'd anything up along the way

Not sure if you were able to hit the track yet? What kind of temps are you getting on the transmission with what ambient air temperature? What kind of transmission temp do you get at the street? Does it warm up fully on the street?

 

[Rodpwnz]

Awesome job, waiting for the good news!

Not sure if you were able to hit the track yet? What kind of temps are you getting on the transmission with what ambient air temperature? What kind of transmission temp do you get at the street? Does it warm up fully on the street?

Original post UPDATED!

It's been great news, all is well and pretty much where I expected and want it to be. I have hundreds of miles on the car since I finished install - zero issues!

I'll answers questions in order:
1. I have not hit track yet, I just finished less than a week ago! Track day is in the works.
2. Transmission fluid temp is typically 160-170F stable while highway driving. Ambient temp is anywhere from 60F to 85F - See pictures from OP.
3. On street, it depends on driving type. Normal driving is 170F-175F, aggresive driving is 175F-180F. Ambient temp was 70-85F.
4. It fully warms up on street, but takes longer to get to temperature(145F+) because the improved racing thermostat allows 10% flow at all times to cooler. OEM warm up was in 10-15 mins, and now I warm up in 15-20mins. Improved racing states the 10% flow is to avoid thermal shock to cooler, and gradually increase cooler temps.

 

[1 old racer]

What p/n did you get

 

[Rodpwnz]

What p/n did you get

I am using the Improved racing FSM165 - It's the full size Transmission cooler with 165F Thermostat core and -10AN internal diameter flow, and I have it paired with improved racing -8AN fitting adapters and Evil Energy 0.5 inch barb adapter(90 degree) to match 0.5 inch OEM hardline diameter + flow.

I had originally contemplated the compact FSC version, but I believe the internal housing is -6AN which is smaller than OEM diameter and may restrict flow.

FSM model is a BEEFY boy - billet aluminum.

 

[Rodpwnz]

Update 10/24//2025: Project was an absolute SUCCESS!

At long last, I finally got the car out to a track day to test out my thermostat and transmission cooling. I am very happy with the results!

Track: Thunderhill West loop - 2 mile CCW
Weather: Sunny
Ambient temps: 70-80F throughout day
Trans temps: 190F MAX
Diff temps: 230F MAX
Engine CHT: 230F MAX

Things to note - this was a shorter track than I'm used to and temps were lower than what I generally experienced transmission cooling issues with. I also short shifted out of habit and was generally less familiar with this track. I plan on going to Thunderhill East loop next month to try it out on a track I'm much more familiar with.

HUGE shout out to Trent Musser! I came to him a couple days before my track day with a few issues on the car and he took time away from other work to get me sorted. He spent HOURS getting me track ready, all on last minute notice to him. Now I'm not saying do this shit to him, but understand the integrity, passion and care for him to do this considering my dire situation. Without him, I would not have made this track day in time. If you're in SF bay area and want the best, I highly recommend giving him a ring. Trent Musser Motorsports: (707)-655-2909. Tell him I sent you.

I am adding this update to OP as well.

 

[Rodpwnz]

Update 11/20/2025: Project continues to be an absolute SUCCESS!

Since last time I went out, I’ve done a drift centric autocross event at Sonoma raceway. And as of yesterday, Thunderhill 3 mile east loop with cyclone!

Track: Thunderhill east loop - 3 mile cyclone
Weather: mostly Sunny
Ambient temps: 60-70 throughout day
Trans temps: 190F MAX
Diff temps: 250F MAX
Engine CHT: 230F MAX

This last track event at thunderhill was my Fiancé’s first track day. Her and I did back to back sessions, so the car was technically going for 40 minute track driving at a time with a few minutes in between as we swapped drivers.

I was paddle shifting, she was in track mode auto shifting. Transmission temperatures were PERFECT. I cannot emphasize how happy I am with the results of this project and modification.

I will continue to monitor and update as we go through winter, into spring and summer where ambient temps will rise into the 90’s and 100’s. I currently have the 165F Thermostat, and I think this is the perfect temp for my street driven and casually tracked car. For more hardcore racers, or at higher ambients, there is also a 145F thermostat. If I ever need more cooling, I can just swap to the 145F core.

Here is a slowmo video of turn 10

Picture from turn 10

Picture from the Cyclone with another mustang buddy

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