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Failure of transmission cooler inside of radiator (w/ pics)

96K views 80 replies 32 participants last post by  notmycar 
#1 ·
Purpose of this Posting:
This posting is intended to show the investigation/analysis of the radiator transmission cooler fittings connection for one failure on 2003 Acura MDX. From reading MDXers.org I have been made aware of the issue that has shown up recently for cars of this age/mileage, I was able to diagnosis it once I saw the radiator overflow tank. I just wanted to add more information to the collective knowledge.
Automobile: Acura MDX (Nighthawk Black Pearl, Base, 2003, 93K miles)
Location: Naperville, IL (Suburb of Chicago, rust-belt)
Maintenance: Radiator Coolant factory installed
Symptoms (November 2011):
• Transmission slippage in all gears that progressively got worse over two days.
• RPMs not matching transmission gear and vehicle speed.
• Found “Strawberry Milkshake” in the radiator overflow tank.
Diagnosis: Failure of transmission cooler inside of radiator.
Repair: Tow car to home, remove and replace radiator.
Analysis of the failure:
• The radiator is a top to bottom coolant flow. The automatic transmission fluid flow is side to side inside the transmission cooler which is inside of the bottom tank of the radiator, immersed in coolant.
• The failure/leakage was internal to the radiator. All external hoses and fittings were still attached when the radiator was removed.
• The inlet and outlet fitings for the transmission cooler (TC) were easily broken off with a little pressure . The radiator and the TC line fittings are shown below:



• The aluminum body of the radiator (core) was removed from the bottom (tank) by prying up all the aluminum tabs that crimp the two pieces together. There is a gasket between the core and the tank.
• Below is a picture of the bottom black radiator tank (coolant) and the aluminum internal transmission cooler (automatic transmission fluid).


• Below is one of the female sections of the threaded fittings on the internal transmission cooler. The other section is very similar to the pictured one.
Note:
• The size of the O-rings compared to the outer flange.
• The amount of corrosion still left after initial cleanup.
• The outer diameter of the inner connection is just slightly larger than the hole in the radiator tank. Since the inside is not able to slide completely into the hole, the outer flange holding the O-ring is held up about 1/32’’ away from the inner wall of the radiator tank. The O-ring is then mainly responsible for keeping the coolant out of the connection.



• Below are the male sections of the threaded fittings.
Note:
• The amount of corrosion on the outer flange.
• The amount of the corrosion on the threaded portion (white hard crusty, lime scale??).
• The red/orange thread lock material seen on only 1 fitting.
• That the inner aluminum tubing and O-rings were in good condition



At this point, I thought the outer tubing, hex nut, and circular flange were all one piece made of aluminum. However, the corrosion between the hex nut section and the circular flange/washer just did not look right to me. It showed flakiness that is normally seen only in rusted steel. I was able to separate it into 3 parts (as shown below):
1. Aluminum tubing with hex nut section.
2. One rusted steel washer in the middle.
3. One rusty steel washer on the outside.



Conjecture on what went wrong with the connection:
• Corrosion around the threads weakened the connection.
• The corrosion could have come from two places.
• Water (and salt, being in the rust belt) can get between the steel washers and the tank and eventually enter the threaded area. There are no O-rings on the outside.
• Coolant might have slipped past the internal large O-rings and also entered the threaded area.
• The internals to the transmission cooler looked good, The end of the cooler fitting had no corrosion and a tight small O-ring.
• The threaded connection eventually starts leaking internal to the radiator.
• Due to the higher fluid pressure, the ATF is mainly forced into the coolant.
• The two steel washers on the outside of the radiator experienced very different corrosion. The washer in the middle that touched the aluminum on one side had major corrosion that might have been caused by galvanic corrosion due to the dissimilar metals (steel and aluminum). The washer closest to the radiator tank was in much better condition.
• The amount of threads that are engaged between the fittings and the transmission cooler core is also a concern. It looks like only 2 rows were ever engaged looking at the fitting. I was able to count at least 5 rows of threads when the corrosion was scraped away. Looking at the threads in the core, it was unclear how many were actually engaged.
• Could the outside washers have prevented the threads from fully being more fully seated?
• Why are the O-rings that seal out the coolant larger than their containing flange?

Summary: The connection of the tube fitting to the transmission cooler had the following issues:
1. No corrosion protection on the steel washers.
2. Potential for galvanic corrosion with steel and aluminum washers placed side-by-side.
3. Threaded mechanism with potential issues.
4. Internal O-rings with a significantly different diameter afterwards.

Prevention:
The reliability of the new radiator relies mainly upon the manufacturer. The only thing I was able to add, was to spray paint the exposed transmission line fitting hardware in an attempt to prevent future corrosion. It is unclear how many of the issues that I had with the previous radiator still appear in the design of the new one. It is also unclear to me, if this could have been prevented with a more timely coolant change.
 
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#6 ·
All:
I replaced the radiator with an aftermarket radiator. It was chosen for availability, price, and perceived quality. Since, I needed the MDX up and running, I was not able to do or find much research on the quality and reliability of a new radiator. Allow me not to name the brand as I do not want to endorse one brand over another based upon my limited knowledge. The new radiator had different hardware for the TC fittings as compared to the OE.

I agree that it is unclear if any routine maintenance could have prevented this as supported by the anecdotal evidence as reported in these forums.

Thanks for the links to the other forums. The pictures are very similar. Below is a quote from one of the Ridgeline threads:
>> My truck has what appears to be a thin stainless steel washer and shows no signs of corrosion. A dissolving steel washer could certainly swell to the point where it pulled out the threads and that's what appears to me to be what happened.
The washers on my radiator definitely showed the same corrosion, one badly rusted washer, one in much better condition.

The main point of the quote was that a steel washer experiencing severe corrosion could "swell" enough to pull on and damage the internal threaded fittings. Time for me to do some more research on the web.
 
#7 ·
Thank you for these pictures, and the analysis. I am not clear: are the cooler line nipples simple threaded connections to the cooler that could be loosened periodically for inspection or even replacement or re-sealing? I have an '05 with 75,000 miles and I'm getting ready to do a cooler bypass with an auxilliary cooler to remove all doubt about the factory cooler, but if the cooler's typical failure point is actually this threaded connection, rather than the physical cooler itself inside the radiator body, it would seem like an inspection of the connection could be made.
 
#10 ·
The connection from the:
- cooler line nipples
- to the cooler line is a threaded connection, with thread-lock on one nipple with the 90 degree bend.

However, this connection holds the large O-ring tight against the inside wall of the radiator bottom tank. See Pic #3 above. So, if you wanted to inspect the connection by unthreading, you will have to drain the radiator of coolant and the cooler of transmission fluid. Replacement of the thread-lock material would also be needed. IMHO, I would not try this. I think there are too many things that could go wrong especially with the large internal O-ring.

I can't figure how the fluids are mixing if it is just the cooler fittings, seems like it should just dump the tranny fluid but not the radiator fluid at all?
The cooler fitting connection is inside of the transmission cooler which is inside of the radiator bottom tank. Once the transmission fluid has breached the thread connection, it only has to get past the large O-ring in (Pic #3) to enter the coolant. The O-ring is held in place by pressure from the the connection that was just breached.

Another way to think about is that the cooler line fitting hex section is sitting right next to the outside wall of the radiator tank(w/ 2 thin washers). The threads and small O-ring are inserted through the hole in the radiator bottom tank and into the female section of the cooler. The threads and small O-ring are about 1/2 in long and resides effectively on the inside of the cooler which is inside of the radiator. (See Pic #2)

If the explanation above does not make sense, I can add more pics or add more arrows to the existing pics.

Good point Hokiefyd. If the connections are visible and can be inspected for corrosion (especially the corroded steel washer) then perhaps this failure could be avoided. I have a 2005 MDX with 158,000 km and am worried. Please let me know how the cooler bypass system can be installed and who to buy the parts from.
Thanks.
I definitely agree that inspections are warranted for this connection.
If a transmission cooler bypass system is installed, the bad connection in the radiator still remains holding that O-ring in place. The connection could still fail at a later time, but only affecting the radiator.
 
#9 ·
Good point Hokiefyd. If the connections are visible and can be inspected for corrosion (especially the corroded steel washer) then perhaps this failure could be avoided. I have a 2005 MDX with 158,000 km and am worried. Please let me know how the cooler bypass system can be installed and who to buy the parts from.
Thanks.
 
#15 ·
Honda Radiator make the Chicago Trib

The same radiator fittings on a Honda Pilot were mentioned in the Chicago Tribune:

Q: My daughter’s 2005 Honda Pilot with 64,000 miles blew the transmission fluid line out of the radiator, fitting and all. Is this a common problem? The bill came to $800, so it is not a small problem.
- R.C. , Glastonbury, Conn
A: Compared to what could have happened, you may want to consider this a small problem. Honda has had transmission issues recently and this seems to be one, but is is even worse if the transmission fluid leaks into the coolant. When the two mix into what looks like a strawberry milkshake, your transmission and radiator are toast, and that will be a big bucks repair. The engine will also have to be flushed. We have not head of many owners getting goodwill fixes from Honda.

Bob Weber “Motormouth”, Chicago Tribune Sunday Feb 12, 2012.
Page 3, Chicago Tribune RIDES

I could not find a URL to reference, so I copied the information directly giving credit to Bob Weber.
 
#17 ·
So that little part is what caused me to spend around 3500 on my 2 month old used car. Man that sucks. The break took out the radiator and the cooler and 2 days later my transmission. Started slipping really bad in first gear whenever I stopped somewhere and tried to go again. Dealer must have agreed that this was a hell of a thing because they paid for 60 percent of the transmission replacement! At least that was good. My 2005 MDX had 83,000 miles on it and no warranty. So They didn't really have to do anything.

Still don't know if I will buy another Acura though. At least my transmission has a 3 year warranty now.
 
#19 ·
Soooo..... If you un-hooked the TC on the bottom of the Radiator and added and exterior TC would this prevent the problem? From the video, and from the posts on here, it is not internally but at the connections. So if I simply add and external TC my radiator may leak where I take out those nipples for the TC, right?

Mike
 
#21 ·
OK guys this exact just happened to my 2006 MDX. Luckily my wife was just a few miles from the house when the thing must have suddenly broke and spilled the tranny fluid quite quickly.

Thanks to your help on this site, I've just finished a 3 day project of replacing the rad, and doing several fill and drain of the tranny fluid.

Luckily, the tranny seems fine. However can someone help me please?? there are two small hoses that connect to a sensor just behind the hood latch for the motor mount control valve. One seems to go to the engine cover and one goes down between the two fans. I've got them mixed up and I am not sure which one connects to the solenoid on the top and which goes on the bottom.

Please Help.

BTW mine only had 83,000 miles on it
 
#22 ·
If at all possible can you post a pic?
 
#25 ·
Quick couple of questions. First the history, my '03 MDX (at 163k) had this issue and the standard failures/repairs were made by a national franchised repair shop.

I checked the tranny fluid level the morning after it was repaired and it was high on the dipstick. Like 1 1/4 inches above the maximum fill mark. I chocked this up to the incline of my driveway and the fact that i checked it before i brought the engine to "normal operating temperature". I drove it that day and everything felt perfect.

Fast forward 1,700 miles.

My rear main seal began to leak, slightly. This seal was not replaced during the tranny job. The leak was small and i was not about pay another $600 in labor to get it done so quickly after the job (about 4-5 weeks later). Yes, they probably should have replaced this as part of the job being done given the mileage, but i am not here to discuss that. It is not an issue.

MDX was/is running perfect and fast forward another 1600 miles or so. Then the D5 indicator begins to blink. I checked the fluid level and it was still about 1.25" above the maximum indicator. Read in the manual to take it to be checked. So i took it in to be diagnosed.

Diagnosed with bad 4th gear pressure switch. This shop was different than the original repair shop and they were not able to get the part for 48 hrs due to weekend. While it was in the shop being diagnosed, i started doing some research at home and one of the posts that i had read talked about replacing this particular switch. By chance it was one of the diy's that i found and watched. It looked simple and straight forward.

After finding out the car would be sitting, i decided to call the acura dealership nearby.
I found the part that day at the acura dealer and replaced it in about 30 minutes.

After the repair i parked the car flat and let the engine warm up. Checked the fluid level again. This is third time it has been checked by me in about 3,300 miles (6-7 weeks). The level was, still 1.25 inches about the maximum mark.

Okay, here are my questions:
1. Is my dipstick the wrong one? It has the yellow handle and the min/max line are the two dot sized holes, so it should be just fine. I can't imagine that two dealers did not check the fluid level and notice this. Am i missing something here??
2. Could this extra fluid be the cause of the main seal beginning to leak after the initial 1700 miles?
3. Does this also relate to pressure switch failing?
4. Is there a way to remove this excess fluid....if this is an issue?? The car has been running perfect since it was initially repaired.

Any thoughts would be great.
 
#32 ·
Well,

I have known about this dormant surprise for a while now and kept meaning to be proactive and change the radiator. But time wasn't to be found.

So at 150k, the day after a 2hour trip, after coming home from daycare a large puddle started forming as I was getting my daughter out of the car.

I am now a humble member of the tranny fluid filled radiator club.

Ordering parts now.
 
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