If you want lower operating temps do a 180 vs a 188 unless you live in a cold climate. Or wait until the shutters are full open and unplug the shutter connector under the hood latch. Never known anyone to drill our thermostats.

 

I've been running a 180 thermostat in my 2018 3.5 for 15 months and 35K miles now. (best mod ever)
My "normal" engine temp hovers around 192 - 194. It spikes as high as 212 pulling hard up hills but immediately goes back down. No idea what my grill shudders are thinking.

 

All, I went ahead and drained the radiator from the peacock. I used a hose, caught a gallon worth of coolant, but had to use a drain pan because it was also just coming out from the opening when unscrewed. I used a new o-ring and oriented the bleeder valve up. I didn't drill it out as planned. I also went with Prestone Max/Platinum as previously recommended on here. It says a 56/44 blend on the jug.

So far the transmission temperature is in the 170-190 range, down from 200-215s. Using the a/c, I'm consistently at 188-190 for engine temps, highway can go from 180-192. No a/c 193-203.

The old t-stat was clearly sticking. I can see where the brass was rubbing and when compressed, it did not return. I'll do a boil test and post those results with the photos. Oddly, there was a spring that looked like a spring from a pen, jammed up in the bottom of opening.

Thanks for answering my questions.

 

No worries. Glad it fixed your issues!

 

Glad it is working better for you.
I just literally took a trip for all the Michiganders here. From the Detroit area to just north of west branch mi.
I never hit 200 degree engine temp. Up until I hit west branch on I-75 my trans temp stayed under 200. The I hit the hills at around exit 215 and finally trans temp hit 201. But once out of the hills it went just under 200 degrees again.
I also have noticed I am getting a tick better fuel mileage since I have installed the 180 degree t-stat.
One of the best things I have done to my truck!

 

Yea, I never mentioned it before but.... I swear my truck has gotten a tick better fuel mileage with this mod. It seems to run better too but maybe it's my imagination.
I installed the 180F thermostat at 100K miles... truck now has 135K miles and performs better than ever.

 

Sorry all, I was not able to do the boil test. The wife has something about car parts and the kitchen counter. Needless to say, the middle of the original unit has what seemed like coils of a cheap brillo pad in there. And very visible witness marks on the center shaft from where the biding of the unit staying open or staying closed. Odd that this happened after the phaser job, but I was just chalking it off to me driving hard. Thanks again to this forum for the guidance. Also, single digits air temp outside and heat is still toasty for the wife.

 

Sorry all, I was not able to do the boil test. The wife has something about car parts and the kitchen counter

Show her this and tell her it could be much much worse:

https://www.f150ecoboost.net/posts/1367259/

 

What do you mean by you had the three overdrive gears locked out?

 

I had the 3 overdrive gears locked out when pulling the trailer.

What do you mean by you had the three overdrive gears locked out?

@adamhosman2020 - I'll assume you wanted to refer to @2016XLT4x4 comment from a few pages ago...
On the 10 speed, gears 8, 9 and 10 are overdrive ratios. You can lock these out using the shifter so the transmission only will go as high as 7th gear.

 

How does this work with the 6 speed transmission? Only as high as fourth or should fifth work well also? What is max speed when towing?