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transmission fluid leak at cooler - confirmed

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MyForthHonda

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Discussion starter · #1 · (Edited)
Here is the source of a leak that's been happening all summer in my 2010 Odyssey. It lost only about about 100-200 ml of transmission fluid. There was a very visible stain on my driveway and all over the right underside of the engine bay. It originated in the right side transmission cooler fitting where it screws into the radiator. It's a replacement radiator. Denso brand. It was installed a year ago, but I didn't see any leak until the weather warmed up. Unfortunately I missed the warranty period. Oh well. But I thought it was interesting and might be useful for others to see. Based on the dispersal pattern of the oil it wasn't clear if it was engine oil or transmission oil. It sprayed all over bottom of the oil pan and the AC compresssor, in addition to the body directly under the radiator. It took some time confirm it was indeed transmission fluid. This was the final confirmation. Determined by cleaning the area then running the car for a short while then letting it sit a short while more. I expect that it is a stronger drip once the fluid is fully warmed up on a hot day. I'm going to take it out and see if it can be sealed with thread sealant before I order a new one. p.s. this is the first leak this vehicle has in since I bought it new. Not bad.

Although I proactively replaced the power steering lines and the transmission cooler tube a year ago to prevent leaks (they were blistered and headed for a leak). The replacement radiator was used because the original radiator experienced minor damaged in the process of removing it in order to replace the catalytic convert heat sheilds a year ago as part of the same work. Denso disappointed me with their after market radiator!

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#2 · (Edited)
With the way these are constructed, I would expect to see the drips under the silver flare nut. That thin nut closest to the plastic radiator bottom tank is for tension against that washer and against a flat, round rubber gasket that keeps coolant in the radiator.

I would try gently tightening the flare nut, first, so see if that solves your leak issue.

Almost, I feel antsy about a possible leak problem between coolant and ATF based on that picture. Just have a bad feeling about it that would steer me to replace that radiator.

Denso makes a good radiator. If you don't want to use them, I've used Koyo products at least three four (edited, forgot how to count) times in very old Hondas (two Odysseys, two Accords) with good success.

OF
 
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Discussion starter · #3 ·
0dyfamily said:
With the way these are constructed, I would expect to see the drips under the silver flare nut. That thin nut closest to the plastic radiator bottom tank is for tension against that washer and against a flat, round rubber gasket that keeps coolant in the radiator.

I would try gently tightening the flare nut, first, so see if that solves your leak issue.

Almost, I feel antsy about a possible leak problem between coolant and ATF based on that picture. Just have a bad feeling about it that would steer me to replace that radiator.

Denso makes a good radiator. If you don't want to use them, I've used Koyo products at least three times in very old Hondas (two Odysseys, two Accords) with good success.

OF
Click to expand...
I took it out in the time since I made the first post. I'm going to snug and reassemble. I couldn't get a wrench on it in the van, and I wanted out out to inspect it properly. Photos to follow....
 
#7 ·
My vote is to sand/polish, and later replace it if this didn't work. But I'm cheap and time has little cost to me! :giggle:
 
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Discussion starter · #8 ·
kernel said:
My vote is to sand/polish, and later replace it if this didn't work. But I'm cheap and time has little cost to me! :giggle:
Click to expand...
Thanks for the vote. It helps. I think that's what I'm going to do. It was never a big leak, isn't under much pressure, and was not even snugged terribly tight to begin with. So it won't be worse than original, and if it doesn't fix it then I don't have to address it immediately. Maybe an ever so slight smear of HondaBond on the face of the flare for insurance. I'm going to take a break and let it sink in before I make a final decision.

Does the return line from the cooler pass through a filter in the transmission? I know that there's a filter in there, and it would make sense, but I'm not certain what the exact fluid circuit it. If I smear a thin film of RTV I'm curious how concerned I have to be about little blob, however slight, makings its way through to the transmission.
 
Discussion starter · #9 ·
Here is the imperfection through a 40x jewelers magnifying glass. You can see the shining ring where the flare sealed all around and then at the point of the imperfection it stops (obscured by glare, but there is a discontinuity at that point). Further, it turns out the little blob is not metal (aluminum), it's a blob of hardened crud. It came right off when I cleaned it with some 800 grit sand paper. I think the root cause of this was simply that the flare was never tightened properly at the factory and simply didn't seal all the way around.

Image
 
#10 ·
MyForthHonda said:
Neither the thin nut that secures the inner heat exchange tube it to the radiator body nor the flare nut were terribly tight.
Click to expand...
Man, that's not good. Glad you caught it before more than just ATF leaked.
MyForthHonda said:
I think the root cause of this was simply that the flare was never tightened properly at the factory and simply didn't seal all the way around.
Click to expand...
(y) (y) (y)

OF
 
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Discussion starter · #11 ·
So I ended with polishing the flare with some 800 grit, and cleaning it. It looked good. Not virgin, but good. I smeared a very thin layer of Honda Bonda HT on the flare and red lock tight on the lower retaining nut, all snugged much more firmly than original. If that doesn't do it, nothing will. It will go back in the van tomorrow. I expect sucess, but I probably won't know until next spring when the weather gets warmer and any drips start flowing. Lesson learned: check these connections on new radiators!
 
Discussion starter · #12 ·
Here's the final result after running the van long enough to bleed the coolant and check/top-up the transmission fluid. Between what had leaked, and what was lost pulling out the radiator, I had to add about 300 ml of transmission fluid. Looks like a success so far. Resolved by tightening two nuts (and adding a bit of sealant to the flare joint for insurance). What a pain.

Image
 
#13 ·
Good work, @MyForthHonda . Enjoy a well-earned adult beverage. I'm enjoying some Bailey's and coffee to celebrate this successful repair.

OF
 
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0dyfamily
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