DIY: Full Flush for Automatic Transmission

Well, because it is kind of expensive, and unless you already know you are low, it's just a waste.

 

I wanted to know because I was curious if the factory under filled it. Which they did by 3/4 qt.

 

Because you’re taking the old fluid out at the same time you’re adding new fluid. If were like an oil change you could just drain it all out and put the right amount in, but it’s not.

 

+1 on all of the reasons above in addition to not allowing the tranny to pump dry when you flush it. Thought I saw something that pumping more than 3 quarts out would increase the chances of having the tranny pump itself dry and do damage. Doing MORE damage while doing maintenance is not the point!

 

Did the flush today and upgraded the tow package cooler to a tru-cool. Mounted it in the stock location with 2 of the 3 stock mounting points. I added 2 more to secure it and relocated the horns. It was an easy job.

Trans runs at the normal temp still. Tried to heat it up but it wouldnt go above 158F. Not 100% sure when the trans thermostat fully opens. I think I'll only be able to test it when I am towing. I'll try to answer any questions.

 

It is actually cheaper. Walmart gets $16 for a gal or $5 for a quart btl. there's almost $20 saved there. And you'd have to keep swapping quart bottles anyway refilling one to pump from just takes a few seconds. Then I have the gal jugs to keep dumping the old fluid into for recycling so it worked out well for me.

 

Anyone getting P0748 after full flush?

 

I just finished this process. Followed the OP’s directions to the letter, except I used my ScanGauge II to monitor transmission oil temperature. Easy job and I had exactly the amount of extra fluid I added drain when checked level. Did the service at 95K on the clock. Mainly because I have no idea how the original owner drove the truck. Old fluid was dark, but still clear and not muddy, so I feel good about the condition of the transmission. Great write up and I figure it saved me >$200, not to mention the piece of mind and satisfaction of performing my own maintenance.

 

You probably already found this, but here's some good info on potential causes and symptoms. https://www.troublecodes.net/pcodes/p0748/

 

Calling @gearcruncher, he seems to be the resident TW transmission expert that I would trust to point me in the right direction.

 

Who did the full flush ?
That solenoid code identifies the transmission fluid pressure sensor .
If for some reason , the truck was running and somehow became very low on transmission fluid , PO748 would trigger .
My first guess is the trans got too low on fluid during the flush or dirty particles from the bottom of the pan accidently managed to travel through the solenoid partially blocking the fluid path .
Try clearing the code and re-test drive to see if it comes back

 

I too upgraded the stock aux cooler to a single Tru-Cool cooler. I bypassed the inline oil cooler.
Here is a short video of my setup:
https://youtu.be/U5w6Wwmahhw

 

What year is your truck? My 2012 does not have a thermostat for the transmission. I just followed what the OP wrote and worked out perfectly. Pumped out 11 quarts, put back 13 quarts without any issue.

 

Which tru cool did you use?

 

It's mentioned in the video. You should watch it, it might help you with your setup. I went with the Tru-Cool 4589

 

I have the exact same cooler setup minus the electric fan. Which fan and controller did you go with?

 

Just a generic aux fan I got on Amazon. It’s a 9” fan. There’s no fan controller. It’s a manual switch on/off when I need to cool the oil, which is rare.

 

I have a 2010. I found a couple posts about the thermostat (like post #11 here), but they look to all be 3rd gen. I did the flush twice now, 45k and 85k, without issues by following the same steps. Im guessing it's new for 3rd gen.

 

The TC does produce a lot of heat, but if you upgrade coolers, like I did, the cooler is large enough to keep up with the heat generated by the TC. The large cooler I installed does a great job at keeping the oil cool when the TC is unlocked. I’ve had to use the electric fan a few times but I am thinking about ditching the fan and putting an even larger cooler, the Tru-Cool 4590 because I know that cooler will do a great job without a fan.

 

I ordered a Hayden cooler to replace my stock cooler on my 2013 Sport. I'm going to install the cooler and flush the system. I see that the transmission cooler lines first run through the radiator, then to the cooler. I'm assuming that I do not bypass the radiator, right?