Ok first thanks for all the awesome helpful content. I have lurked on here for years and it has been so helpful. I hadn’t seen anyone having the problem I am so I figured I would make an account and join in the conversations.

2008 F150 5.4v 3v always ran premium 5w20 full synthetic from mile 0. (Amsoil mostly but also pen oil ultra plat, and royal purple)
repairs done: spark plugs changed, one fuel injector changed, spicer rear differential cover installed, transmission rebuilt in 2019 with about 10k miles on it, external cooler added by the shop that did the transmission. FFD stage 3 electric fans added in 2021.
Ok here’s the problem…. Leading up to the transmission rebuild the truck (trans?) would overheat when idling for long-ish periods of time. Think school pickup line, or multiple drive this that are slow, in the south Alabama summer. Code on dash “transmission malfunction.” Overheating still occurring after trans rebuild and cooler install. Trans shop recommended updating computer which would tell the fan clutch to turn on sooner ($300). I opted to spend that money on electric fans. Installed them myself. Still overheating. Also the actual engine overheated during this time and coolant boiled out of the reservoir - during school pick up. Dropped truck at trusted mechanic and they diagnosed for days only to not charge me and give up. Said the truck and trans were overheating and fans didn’t come on or stay on in time to cool it. I ran the green AC wire of fan wiring to a switch in the cab to allow me to manually control when fans are on or off. This helped but hasn’t solved it entirely.
so there it is, i am hoping someone can help point me in a direction to go. I have thought about throwing parts at it but am not made of money. Ideas I’ve had: transmission pan with cooling fins and higher capacity (aed makes one), new trans cooler -maybe with its own fan, thermostat change (190° or should I maybe get one that opens sooner?), water pump change?, radiator change?, alternator upgrade/change (to be sure fans are getting max volts- I installed eBay volt gauge and it stays around 14.0v).

TLDR: transmission and occasionally engine overheat when idling for any length of time. Electric fans installed. No codes other than “trans malfunction.”

thanks in advanced everyone

 

Thought it was relevant that the transmission shop isolated the transmission cooler they installed. So it no longer routes through the radiator. They said they do this to avoid any risk of contamination of rebuilt transmission with any metal shaving that could’ve been in the old system.

 

I'd go back to a stock configuration and then figure out the overheating problem
You need both trans coolers
They said not to use the radiator cooler in case your engine is messed up (and shooting compression pressure into the cooling system) which can put coolant in the trans and ruin it quick
You need the stock cooling fan, it will flow more air than just about any electric

If you use a thousand dollar electric cooling fan like off a Ford Flex, it will flow enough air
I would just use the factory clutch fan and an aux trans cooler like the HD cooling ones had and the bigger radiator the HD ones had
Your base engine may be the problem, head gaskets, or a crack somewhere
They want the trans fluid and the coolant to be the same temp, can you check the trans fluid temp in live data on your scan tool? and ECT voltage?

 

"coolant boiled out of the reservoir "
A recent thread used the same wording and it turned out to be a leaking head gasket causing the coolant to boil out of the reservoir.

 

thanks this gives me a starting point. I still have the brand new oem fan clutch so I can put it back on there. I would think I need to get the computer updated like the trans shop (and ford dealer) recommended if I do put the fan clutch back though. Bc it was overheating the transmission with the new fan clutch. I don’t have a scan tool currently but I certainly don’t mind having a reason to buy one. (Any suggestions?)
I work offshore so I am planning ahead for Jan 7 when I ge home. My plan for now will be to put fan clutch back on. Change the fluid , update the computer (which they say will make fan come on sooner, and what do you think about installing that ppe aftermarket trans pan that holds more fluids - cools and has a drain plug?
also saw a product that installs on the bypass line to allow coolant to always flow through radiator. Would that be worthwhile?

 

The next scan tool I buy will be an Autel bidirectional one
You don't need a 1300 dollar one
I will buy a cheap one that will do what I need for now
Which is, check my Mercedes over, and be able to tell cars to do things like turn the vacuum pump on, on Mopars
Bidirectional just means it can tell the processor to do things

 

My Ford NGS scan tool does all that, but just up to 2005 Blackwood
Generally, they will just use cooler cleaner and backflush the cooler in the radiator until the stuff comes out clean (that's what I do)
Absolutely on the trans pan, Mine is a E4OD, 475 dollar Hughes HP4680, finned aluminum, holds about 4 more quarts than stock
I think you should get a second opinion from a guy like Precision Transmission in TX about the cooler bypass line
I'm not sure what yours has, or whether it has one like a E4OD with the check valve
I would damn sure run two trans coolers and get a FLT sensor in there to check the actual temp