Here's the real question:

If, in theory, the fluid in a transmission goes from 100% (new) at 0 miles to 0% (worn out) at 30,000 miles what's better for the longevity of the transmission?

1. As the fluid ages and wears out, the transmission is running on older and older fluid, until the fluid is worn out. Then a complete flush is done and the cycle repeats. You go from new fresh fluid to crap over 30,000 miles. The fluid get more and more worn out.

2. Let's say you drain 8 quarts out instead of flushing at 30,000 miles. You'll have 45.71% fresh fluid in the transmission. Then you drain another 8 quarts every 7,500 miles. Now you have 8 quarts or 45.71% of 100 percent fresh fluid in the transmission and 45.71% or 4.34 quarts of the remaining fluid has 7,500 miles on it and .the last 5.16 quarts has 37,500 miles on it.

The average mileage for the fluid in your transmission at this point is about 13,000 miles.

If you can keep the "mileage mix" of the fluid in the transmission constantly between 13,000 and say 17,000 miles, is that better than running the transmission on fluid that starts out at zero miles, goes to 5,000, 15,000, 20,000 and finally 30,000 miles?

I speculate that starting with 100% fresh fluid every 30,000 miles does not offset the extra wear on the transmission caused by ever dirtier and worn out fluid in say the last 15,000 miles.

I think I'd rather have an average of 15,000 mile fluid in my transmission all the time rather than 20,000 mile old fluid at 20,000 miles and 29,000 mile old fluid at 29,000 miles.

If you drain the pan twice at 30,000 miles, You'll start the cycle with 70.53% new fluid. Drain it three times and you have 84% new fluid in the transmission and lower the average mileage of the fluid accordingly.

 

Good to know, but as long as my local O'Rielly's can supply me with Mercon SP for $4.59/quart, I'll pay the 34 cent/qt. premium.

 

I hear ya.Ive changed to the valvoline cuz i can get it at any parts store when i want.
If i could get the ford stuff anywhere id probably have stayed with it.I usually never hit my 25k at home always on the road.And i perfer to change it at the track we tend to have plenty of down time and plenty of waste oil dumping areas..

 

O'Reilly's is great for ATF, but they're pretty dumb when it comes to synthetic diesel oil. I noticed the always have Mobil 1 for Turbo Diesel Trucks on the shelf. Great! I'll pick up 4 gallons...

What? there's only three gallons on the shelf. The store manager says he can get an extra gallon tomorrow, but corporate says they're only allowed to stock three gallons on the shelf.

I call the clown in charge of marketing and ask him if he thought O'Reilly's would sell more M1 TDT if they stocked FOUR gallons on the shelf because THREE gallons isn't enough for one oil change on a 6.0 (and as far as I know) any other diesel pick up.

Now, I buy Rotella T6 across the street at Walmart.

 

The tranny holds closer to 18 quarts.

But who cares, some folks have "picked" at details and made comparisons to oil changes and air in tires (useless sarcasm IMO). Ljutic's point was exactly that there is so much left in, that one simple drain every 30k miles will eventually leave a LARGE amount of fluid that is quite old in the system.

The transmission fluid change issue is really a unique situation, and if you can get the transmission life out of multiple approaches to the fluid change it is good information - simple as that. Encourage discussion and we all learn (well except those that know it all already).

To address the earlier posted estimate that 90% was new:

Assuming the pan drain is 8 quarts, 8/18 is apprx 44%, repeat and you get apprx 69% of the way there, repeat and it is apprx 83%, repeat and it is apprx 90%., etc. (same approach as XB70's, and essentially the same #'s)

So ........ It takes 4 changes to get apprx. 90% of the fluid new. Even if you drain 4 times every 30k miles, at 150k miles you will still have SOME fluid in there that is 150k miles old, less than 0.1 quarts though. Also you will have some w/ 120k miles (apprx 0.15 quarts, some w/ 90k (0.35 quarts), some w/ 60k (apprx .9 quarts). Is this enough for 300k miles of reliability - who knows, but I would hope so.

BTW - Ford states that a flush every 30k miles is an acceptable practice also.

With the tranny fluid, I doubt that the oil itself wears out, The issue would be more likely to be particles in the system (filtration inefficiencies and particle deposit) and depletion of the additive pack (detergent, viscosity adjusting polymers, etc).

Since changing 8 quarts 4 times is pretty expensive, personally I would think a good flush periodically would be wise - at least every second or third interval of 30k miles. Problem is, it is VERY hard to find a shop (dealerships included) that have a hot flush machine.

What would be useful information would be for someone to list the transmission flush machines that acceptably deliver a hot-flush (I believe the target is to get the system over 170 *F).

 

8 quarts x 4 = 32 quarts x $4.59 for Mercon SP = $144.68

Can you buy a Mercon SP/LV flush for $150?

What's the probability it will be done correctly?

How much leftover regular Mercon or Dexron will be in the flush machine when your flush is done?

I'd rather drain four times at home.

The Ford spec for fluid capacity is 17.5 quarts including filter.

 

Yes, you can get a flush for around that price (less when you wait for specials). At my first 30k inteval, I had it flushed for $130. I hear you on all of the flush questions and I agree, that you might not get the job you think you are getting. Same w/ all mechanic work though - the key is finding the shop/person that you trust.

The thing about draining it at home is that you have to drive it quite a bit after each drain. It doesn't fully circulate until the temps get to 170*F or so. If a person doesn't have a TFT gauge, they might not get the new fluid mixed in w/ the old each time. It is not the quickest thing to do - getting these transmissions up to 170 without towing.

All that said, I did the 4 drains at my last 30k interval.

 

with a flush done at the dealer how much fluid are they running threw it to get 100% new fluid?the converter would be the problem with the flush.I would think if they flushed it with a machine and say 10-12 gallons of fresh fluid youd have 10% old fluid left.Once its mixed in the converter its mixed. if the system holes 18 and there is 8 in the pan iam guessing near 6-7 in the converter

If and when mine fails ill pull it and rebuild it myself

 

According to Mark Kovalsky, the thermostat does not shut flow off completely. Even ice cold, there is 10% flow with the thermostat closed, so warming up to 170F is a myth. Since I can put a 5 gallon bucket under the transmission of my FX4 without jacking anything up, drains are pretty easy. Besides, you don't have to do multiple drains back-to-back, you can do one or two today, one next week, etc.

I asked Mark about the thermostat on this thread (posts 16 & 17):

https://www.ford-trucks.com/forums/1...estions-2.html

 

The cheapest retail Mercon SP is $4.59 per quart, so I'm sure they'll run 40 -48 quarts of genuine SP/LV through your transmission and install a new filter for $130. Absolutely positive.

 

Good to know the 10% flow info. I would still like to know how much flow that is though. It could take several hours of driving to get good mixing.

 

I love thought experiments! You've determined hard data without testing anything, just used your thoughts. Imaginative!

Actual testing shows that by flushing with about 10% more ATF than the transmission holds the machines change about 95% of the fluid. This was determined by testing ATF contaminant levels before and after the flush.

The TorqShift MUST be over 170°F so that there is full flow to the cooler lines. If it is below 170°F there is some amount of old fluid diverted to the pan instead of out of the cooler lines. By the time it cools to about 160°F 90% of the old fluid is heading to the pan instead of out of the trans.

 

Could you post those test results?

 

Since Mark K joined in, it's time to ask what's better:

A complete flush wherein the fluid goes from new to X level of contamination over 30,000 miles

or

a series of partial changes over time that keep the weighted average of the fluid in the transmission at, let's say, 12,000 miles old?

 

No, I can't. They don't belong to me.