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Discussion Starter · #1 ·
Not a problem. A few questions...

I was reading up on flushing transmission fluid and there seems to be a big deal made that a flush has to be done with a heated machine because - as soon as the new/cooler fluid hits the temp sensor - the trans will go into bypass.

I was looking at this document here (which is very informative, btw):

http://shop.ukrtrans.biz/wp-content/uploads/catalogs/5R110W.pdf

...and it shows that the TFT is connected to the PCM by two wires and that it is a simple thermistor - temp change = resistance change.



This text and chart describes it in more detail.



The cool thing about the thermistor resistance being higher for lower temps is that - with everything connected as normal - putting a 3Kohm resistor between orange/black and orange/white at the PCM connector will cause the PCM to think that the the trans fluid is 185-190F.

Questions...
Wouldn't this force it out of bypass? Is there any other problem with doing that for a short time for the purpose of a flush?

My other question is how much additional fluid from above the TFT is released when that sensor is removed?

Thanks.
 
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Discussion Starter · #2 ·
I'm gonna bump this because I posted it in the middle of the night. It rolled off of the active list before morning.
 

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That would work. I don't know what percentage or flow would make it through the flush filter. 60-90 minutes to circulate all of it is just my best guess.
 

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Discussion Starter · #4 ·
Thanks for the confirmation and info. I've been thinking about a 2008 pan/filter swap and wanted to figure out a good flush method.
 

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One thing to consider, unless you had a problem and have debris in your system, the roll filter actually works extremely well; so a flush may not be more than wasted effort, even if your last fluid change was 100k late or never.
 

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Discussion Starter · #6 ·
One thing to consider, unless you had a problem and have debris in your system, the roll filter actually works extremely well; so a flush may not be more than wasted effort, even if your last fluid change was 100k late or never.
Got it. The trans fluid actually looks like it is out of a fresh bottle. Mostly, my pan and filter swap means switching to LV. I was thinking that a flush might be in order, but that doesn't seem necessary from my reading.

That reading and your knowledgeable input is causing me to lean towards drain and fill. Faking the PCM with a 10¢ resistor would still be cool, though!
 

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i have never trusted the heated flush 100% as I have tried to warm up the trans to 170 with blocked airflow and it never came close and then having the incoming fluid at 170* is another iffy deal so IDK how ford does it but they don't trick the tstat

so i fear the flush is not 100% new for old swap

that being said i have the 08 pan and filter and the TP this way both circuits are filtered and the coolers protected from debris and the intake that used to be a screen


a pan drop and compressed air at the TP filter orfice gets you a good amount of fluid out then maybe do it again in a day or so and boost the% of new fluid
 

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Discussion Starter · #8 ·
Appreciate the info, @ZMANN.
 

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Not a problem. A few questions...

I was reading up on flushing transmission fluid and there seems to be a big deal made that a flush has to be done with a heated machine because - as soon as the new/cooler fluid hits the temp sensor - the trans will go into bypass.

I was looking at this document here (which is very informative, btw):

http://shop.ukrtrans.biz/wp-content/uploads/catalogs/5R110W.pdf

...and it shows that the TFT is connected to the PCM by two wires and that it is a simple thermistor - temp change = resistance change.



This text and chart describes it in more detail.



The cool thing about the thermistor resistance being higher for lower temps is that - with everything connected as normal - putting a 3Kohm resistor between orange/black and orange/white at the PCM connector will cause the PCM to think that the the trans fluid is 185-190F.

Questions...
Wouldn't this force it out of bypass? Is there any other problem with doing that for a short time for the purpose of a flush?

My other question is how much additional fluid from above the TFT is released when that sensor is removed?

Thanks.
To answer this....NO it will not force it out of bypass as the actual thermostatic valve is mechanically controlled NOT electrically. I.E. it exactly the same as a thermostat. The hot fluid has to hit it and cause it to open. The computer will think the temp is higher then normal, but this only (as described in the above post) changes TCC lock and shifting scheduling. The thermostatic valve is located in the pump housing and is tiny. If you were to hook the machine up properly (to an outlet of the transmission housing) you will still get the flush done. There is always some fluid that is pumped through the system, although the pressure is low in P and N. You can drive the truck around and get the trans hot and then hook the machine up and with it on jack stands, leave it in drive and let it idle. This increases the pressure to a point that some will be pushed pass the thermo valve and flush the system. A heated machine is best, as it keeps the valve open and flushes at higher pressure.

Using air will NOT get very much of the crap out of the cooler at all. The difference between a flush machine and trying to do it manually, even with a product like trans flush when apart is night and day. The coolers in these really hold a bunch of crap that needs to be under pressure to remove. Also recommend pulling the TP filter out when doing this.....just eliminates trying to flush the crap out of that filter for no reason as you should replace it once the flush is complete.
 

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Discussion Starter · #11 ·
Got it, Toren. Was not aware of the mechanical thermostatic control. Sheesh. For as much electronics as is in that thing...

So - to swap the pan and internal filter - would it be best to hot flush and then do the swap?
 

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Well heres the thing...being that ive done a few hundred flushes in my time....99.9% of the time when we did a flush. Afterwards i always checked for DTCs . Ive never even once had a trans to go in to failed management. I'm not saying its isn't possible. But it was always smart to ask the customer when they wanted a flush IF THEY WHERE HAVEN ANY ISSUES!!!! There is a lot of gray areas in automotive world...Now Mercedes Benz and BMW is a different story. You do have to watch them cause they will go in to failed management due to a flush..... Im just saying ive never seen a super duty do that in the 20 plus years of working in a shop with super dutys. Most of the time the TFT sensor is used to monitor for a over heating condition cause they will blow the fluid out of them if they get to hot. And that is programmed into the PCM as a value to where the overheating point is .
 
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