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Discussion Starter #1
I purchased an early 99 f250 a few years back and have used it to pull my 32' fifth wheel camper about 6 times and just used it to drive here and there. Its a good solid truck, shifts great and I have a tuner on it with a 40hp tow program which works well. When I bought it I was told that "the dealer" had just installed a "new" trans. The transmission was clearly a fresh install and looks like it might be a ford factory rebuilt transmission. It has a serial # decal on it.. not sure if it means anything.

anyhow, I noticed a slow ATF leak and sourced it to the factory hoses that connect to the factory oil cooler. Looks like where they went from metal to rubber failed after 21 years. Go figure.

So, rather than pulling the stock cooler, getting a wrench on the fittings to take the hoses off, buying the correct fittings (my cooler is not a barb/clamp deal) and then putting it back together the way it was I bought a used 26 row off a 6.0l truck so it isnt a complete waste of time. I will install a filter on the output of the used cooler so I dont think debris will be an issue if there is any.

My question is; what ATF do I use since I dont know if its synth in the trans now? The fluid looked nice and red last time I looked at it so really dont want to pay to have it flushed and for new fluid etc..


Can someone who really knows the answer to this lend a brother some information.

Im attaching a few photos for your enjoyment. Two show the transmission (serial decal on one) and what should show the leaking cooler line..

thanks
 

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It absolutely will not hurt to mix transmission fluids as long as they are approved for your transmission. For the 4R100, that would include Mercon or Mercon V. Mobil 1 ATF is a good choice if you are towing as it is a full synthetic. Valvoline Max Life is another that will work. Does your truck have the fluid cooler in the bottom of the radiator? If not, I would upgrade to that.


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I would run some new warm fluid through the new cooler with compressed air and see what comes out. Running with the new filter is a good idea.


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Discussion Starter #4
It absolutely will not hurt to mix transmission fluids as long as they are approved for your transmission. For the 4R100, that would include Mercon or Mercon V. Mobil 1 ATF is a good choice if you are towing as it is a full synthetic. Valvoline Max Life is another that will work. Does your truck have the fluid cooler in the bottom of the radiator? If not, I would upgrade to that.


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No, no water to oil cooling. Is it worth it to upgrade my radiator?
 

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No, no water to oil cooling. Is it worth it to upgrade my radiator?


My truck came from the factory with only the small trans cooler and no radiator tied in. It would get hot I upgraded to the 6.0 31 row cooler and have had no problems since. During the winters in Colorado it runs 125-135 degrees and summer it hits 150 -175. I would tie in the cooler and put a temp gauge on it to see what it runs. I don’t think it worth it.


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No, no water to oil cooling. Is it worth it to upgrade my radiator?
I'd say yes. A new Spectra radiator from RockAuto is less than $120 and oil to water cooling is much more efficient than oil to air. You probably would get away with it towing flat in cool weather, but try to haul something heavy uphill and you might be glad you spent the extra C note.
 

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For the 4R100, that would include Mercon or Mercon V.
Nobody has made MERCON since 2006. Use MERCON V.

The radiator cooler becomes very important at low speeds, especially when backing up. If you are backing a trailer, especially if you're backing up any grade at all you really need a cooler in the radiator.
 

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Discussion Starter #8 (Edited)
thanks for all the responses. I will pickup some mercon v rated atf, synthetic. Sure wish i knew what was in there.. thinking I might drain out what I can and refill the remainder with synth to be sure it has a good qty.

Any comments on the following procedure:

  • Disconnect radiator cooler and drop hose into a container.
  • Turn on truck and watch the container fill.
  • Watch for air bubbles and as soon as they are seen shut off truck.
  • Note qty drained
  • Fill with same qty drained
  • Test drive truck, get hot and check fill stick, top up as needed.
Saw it on you tube but I dont trust much on the internets these days.


I will consider the radiator change. Noted comments about low speed driving. Water to oil or a fan would assist.. but actually, if you think about it, the stock cooler is fan cooled.

EDIT: Would really like comments on this ATF replacement procedure for the DIY person.
 

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Nope. Nobody makes MERCON. Many companies make a fluid they call DEX/MERC. They say it is for use in transmissions that required MERCON or DEXRON fluids.

The difference is that when Ford and GM were licensing the production of MERCON and DEXRON there was a process where the manufacturer had to submit fluid to the OEM for testing. Ford and GM had tests to confirm that the fluid met the specifications. We even built transmissions to drive test the fluids. I was one of the raters of some fluids many years ago.

Now anyone can make a DEX/MERC fluid and say it is for use where MERCON or DEXRON was specified. But does this fluid meet the specs? Nobody knows. It is entirely possible (I'm not saying this happened, but it could) that a manufacturer has a couple thousand gallons of TYPE F fluid laying around. They can bottle that and sell it as DEX/MERC. Is that ethical? Not at all. But they CAN sell it as DEX/MERC because there is no specification for DEX/MERC, and nobody watching what specs that fluid really meets.
 

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Nope. Nobody makes MERCON. It is entirely possible (I'm not saying this happened, but it could) that a manufacturer has a couple thousand gallons of TYPE F fluid laying around. They can bottle that and sell it as DEX/MERC. Is that ethical? Not at all.
Like when some company had a few thousand gallons of leftover Mercon and relabled it as “transfer case fluid” and told everyone Mercon V would blow up their transfer cases (until they sell it all and Mercon V will magically become ok for that application too...)


I see the distinction you are making with labeled as Mercon and officially blessed by the Ford marketing department as such.




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I see the distinction you are making with labeled as Mercon and officially blessed by the Ford marketing department as such.
The engineering department, not the marketing department.
 

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I’ve read too many Dilbert cartoons. I must be getting cynical.


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Discussion Starter #15
Got it.. Drain from the transmission not the cooler.. makes sense.

I hate to replace all the fluid without doing the filter. Although I will be installing one of those mini filters on the cooler output.

I know the dealer didnt do the install... otherwise one would be there already. Makes me wonder what the background is on my transmission.. I guess I will never know unless is disintegrates while I own it. I feel as though Im going to own this truck for a long long time.. feels like an old friend everytime I get in it.
 

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I hate to replace all the fluid without doing the filter.
That's up to you. I don't replace the internal filter. If that filter has enough junk in it that it needs to be replaced the trans is destroyed already. A new filter won't help it.

I know the dealer didnt do the install... otherwise one would be there already.
I don't know that. Ford stopped requiring those filters with a new/rebuilt trans installation several years ago.
 

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When I had my trans rebuilt by a trans shop they did not put a in line filter in after it was done. They did a hot flush machine on it for several hours to clean my trans cooler and lines.


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Discussion Starter #18
That's up to you. I don't replace the internal filter. If that filter has enough junk in it that it needs to be replaced the trans is destroyed already. A new filter won't help it.


I don't know that. Ford stopped requiring those filters with a new/rebuilt trans installation several years ago.


WOW.. cant believe they would do that. If a trans goes bad then the cooler is full of junk. Well, she shifts great so if there is anything caught in the internal I just hope it stays there and the little filter on the cooler will give me piece of mind that even if the used cooler I bought had something in it it will be caught. If my thinking is wrong on this dont tell me, let me just have my little happy fantasy and obliviously go about my life.
 

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If a trans goes bad I consider the cooler bad, too. It goes in the trash and a new, clean cooler goes in it's place.
 

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Discussion Starter #20
If a trans goes bad I consider the cooler bad, too. It goes in the trash and a new, clean cooler goes in it's place.
Agreed, but this wasnt done when mine was replaced and Ive already put 10k or so miles on it. So Im gonna drop in the little filter I received yesterday. Whats done is done. Right now my transmission is working as you designed it to so Im hopefully by keeping it at the temperatures you determined safe it will continue to work for me for many miles to come.
 
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