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Hello everyone
I have an 08 MDX with 109 miles on it. Last Wednesday, we had a huge transmission fluid leak from the engine coolant reservoir, it was bubbly red/brown in color.
According to my wife , the car gave a "check Charging system" and the battery sign came on when it all happened, luckily about couple yards from home.
Yesterday, I took the old radiator out and confirmed it was the same issue reported multiple times on the first Gen MDX.
I flushed the engine coolant with a water/garden hose and installed a new OEM radiator.
I also drained the ATF from the draining bolt located underneath the transmission. I had about 3 quarters out. The I had to put about 6 quarters to get the ATF to the right level on the dipstick.
After filling up the radiator, putting everything back together , i took it for a ride to test the radiator and transmission.
It looks to me like the tranny is shifting right, but I am kind of worried that Some of the engine coolant had leaked into the transmission. The ATF i took out was pretty clean, and didn't have signs of water in it. But since water is heavier than oil,I think it's kind of hard to see if there was any. I wanted to know if there is an easy way of determining if my ATF was contaminated ( without chemical analysis ). I also wanted to know the best way to change ATF : is it through the draining bolt with the engine off or through the hose that takes the ATF from the transmission to the radiator with the engine on?
Thanks for your help and usual guidance !
 

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1.- If the ATF came out clean (Not brownish) it means there is not enough contamination to be noticed.
2.- You keep saying "transmission coolant" but that doesn´t exist you mean the ATF? Transmission Fluid cools down by heatsink in the radiator and a external air cooler.
3.- The best way to replace the transmission fluid is by the usual drain and fill method with the engine off. The other method you are thinking of with the engine On is far more elaborate.
 

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Discussion Starter #3
Thanks for the reply.
You re right, what I keep calling tx coolant is actually called ATF.

The ATF came out clean, red in color and there was no signs of bubbles or brownish color.

The second way I referred to is the one described in below video , i beleive one of this forums member made it. It is definitely more elaborate than using the draining plug. But is there any advantage to do it that way ?

https://m.youtube.com/watch?v=F72WUfqrewY
 

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That method is for when you are trying to replace the entire transmission fluid in the transmission which is around 9quarts.
Is not used for a single change method.
 

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Discussion Starter #5
Update: i did 4 ATF change with 3 quarters each time. There was a clear difference in the extracted ATF color. comparing these colors, I finally think some of the engine cooler made it to the transmission. I used 4.5 gallon of clean ATF total and planning to do it again with my next oil change, probably in a minth or so.

Do you think adding a Magnefine inline filter can help clean the transmission st this point ?
Is it better to put it on the hose that takes the ATF out of thd transmission , or on the return ine ?

Thanks again
 

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A filter wont harm anything, it can only help.
 

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So it appears that I am having the same issue with my 08 MDX with 180K KM. At first I thought the transmission cooler hose burst as I was seeing red fluid all over the floor. But upon more diagnosing, there is transmission fluid in the coolant.

After some google searching, seems like this is a common issue with the MDX. It's at the shop right now and my mechanic said the same thing, he's seen this before. The fix approach:

1) New radiator
2) Flush and clean the coolant passages with a detergent and refill with fresh coolant
3) Drain and flush transmission fluid. He mentioned that if there is coolant in the tranny, it's just a matter of time before it's game over. Even with regular flushes, there are crevices that cant be flushed 100%.
 

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It is getting scary. Wonder what percentage of radiator are likely to fail like this.
 

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Probably most of them... Seems to be worse on the freezing states though, all of them seem to fail because of rust.
Better to do the Bypass before it happens.
 

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I see. Thanks. Hopefully people who follow up this thread will disclose their location and likely cause of failure. Is it necessary to replace radiator at around 150k miles as a preventive measure?
 

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The radiator is fine, I would just bypass the ATF Cooler instead.. New rad is about 130 bucks aftermarket and quite more expensive OEM..
Bypassing the ATF Cooler is 40 bucks.
 

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On RockAuto, a Denso rad for MDX is about $166 shipped. Since I consider Denso OEM or near OEM quality, the price is actually very reasonable. This is more than $40, but it requires no skill :)

On the other hand, how can you by pass the ATF cooler? If you do bypass it, don't you need an external cooler? Then how can we do it with $40 bucks. Very interested. Thanks.
 

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I firmly believe that replacing the radiator is actually more complicated and elaborated than by passing the OEM ATF Warmer.
Did you look at my DIY? My ATF cooler was 30 bucks with the extra 4ft of tubing and extra clamps it went up to 40 bucks. http://www.mdxers.org/forums/74-second-generation-mdx-2007-2013/124609-diy-install-atf-cooler-2g-mdx.html

I cant seem to find a better deal on my specific cooler than this https://www.amazon.com/Hayden-Automotive-404-Ultra-Cool-Transmission/dp/B000C39C7M

But for that price I would rather get the better more efficient cooler for an extra 3 bucks https://www.amazon.com/Hayden-Automotive-678-Rapid-Cool-Transmission/dp/B000C3DDKO/ref=sr_1_2?s=automotive&ie=UTF8&qid=1475395962&sr=1-2&keywords=Hayden+rapid+cool
 

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Thanks. Will keep it in mind. My car is relatively low mile (80k) and I am in CA. So I probably will do this next ATF change which is about 95k miles.

Interestingly, on AMZN the 2nd cooler is shown compatible with 07 MDX. The first one is not. Don't know why.
 

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Thanks. Will keep it in mind. My car is relatively low mile (80k) and I am in CA. So I probably will do this next ATF change which is about 95k miles.

Interestingly, on AMZN the 2nd cooler is shown compatible with 07 MDX. The first one is not. Don't know why.
Beats me... They are universal Coolers they should fit anything and the first one did fit :D
 

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I'm in Toronto, so yes...the winters up here will definitely shorten the life of the parts. For me, it's already too late. If I had known, I would have went with the aftermarket solution. But since I am getting a new rad put in, It is safe to say that it will last the lifetime of the vehicle...I mean, its already a 9 year old car....
 

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I'm in Toronto, so yes...the winters up here will definitely shorten the life of the parts. For me, it's already too late. If I had known, I would have went with the aftermarket solution. But since I am getting a new rad put in, It is safe to say that it will last the lifetime of the vehicle...I mean, its already a 9 year old car....
Thanks for the update. Now that I think about this, I am still confused. If radiator breaks down inside and coolant mixes with ATF, adding an external ATF cooler won't really help radiator. It simply reduces the damage and repair afterwards, right? The radiator would give up anyway.

Also I am surprised that the radiator would leak inside. My old Toyota's radiator once leaked b/c the plastic tank on top of it developed a long, horizontal crack. So I thought an all aluminum radiator can run forever. And I hated the design with top and bottom plastic tanks. But if it can leak inside, those plastic tanks are less of a sin. In fact, it is good that they break down first and the damage is less. Would love to hear others' thought on this.
 

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One scenario was to add an aftermarket cooler to the existing OEM system. If the radiator's internal wall, which separates the different fluids were to breakdown, the fluids would mix.

Another scenario was to bypass the portion of the radiator that contains the tranny fluid, after the aftermarket cooler was added. So, now the only fluid in the radiator is antifreeze. If the wall breaks down there is no mixing of fluids.

Someone points out that the tranny compartment, within the radiator, needs to be plugged off. You can take a hose and connect that tranny compartment's in port/plug to its out/plug.
 

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Thanks for the update. Now that I think about this, I am still confused. If radiator breaks down inside and coolant mixes with ATF, adding an external ATF cooler won't really help radiator. It simply reduces the damage and repair afterwards, right? The radiator would give up anyway.

No.. Bypassing the Internal ATF Warmer means that when the ATF Warmer FAILS there is no loss of ATF = No Transmission Damage.
In order to make the Antifreeze stay inside the radiator you have to plug the ATF Warmer Plugs. In an event of Failure if you correctly bypassed the Radiator you should not need to intervene in any way.. As you have correctly fixed both issues and you can continue to use the radiator with the failed ATF Warmer.

What fails in the ATF Warmer is the joints between the ATF Warmer (Inside the Radiator) and its IN/OUT Plugs, They corrode and allow ATF to leak into the radiator. If you have by passed it there is no ATF Contamination and since you plugged both IN/OUT Plugs there is no Antifreeze loss instead.
 
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