Aftermarket cooler as only cooler?

[Hokiefyd]

Do you see a significant drawback to installing an aftermarket ATF cooler and completely bypassing the cooler in the radiator? The OEM setup, even with the additional cooler for towing, runs in series with the cooler in the radiator.

Our MDX has 75,000 miles on it now and it's getting to the point where cooler failure in the radiator is getting more likely. That nearly instantly ruins the transmission. This is an extremely common problem on MDXes and Pilots. Taking the weak internal transmission cooler out of the equation removes the main variable with transmission longevity on the 2004+ MDX/Pilots.

I'm thinking that an external cooler, especially in our fairly moderate-to-warm climate, won't hurt anything. If I lived in Michigan and routinely drove in sub-freezing weather it might be an issue, but as I see it the only thing I could lose here is a touch of efficiency with "thick" ATF (which is awfully thin anyway). I do know the stock cooler will actually act as a warmer in cold weather, but again, I don't see a huge drawback in our moderate climate down here.

My other option, obviously, is replacing the entire radiator, but that's a more invasive (and costly) procedure that I'd rather not do if I don't have to.

What do you think?

 

[rshaw125]

I had a similar situation with my Explorer. The dealer replaced the radiator twice under warranty. It would leak out of the cooler fittings. A drip here and there. I got tired of the dealer and thought hmmm it has the tow package. Sure enough there is a big auxiliary cooler behind the grill.I put a length of trans cooler line to the ends of the factory metal lines. By-passing the cooler in the bottom of the radiator. No more drips and the aux cooler has worked fine since last Spring. I triple clamped the hose and not a drip since.

 

[Hokiefyd]

Thanks...and no issues in the winter with sluggish shifting because of cold fluid or anything like that? Here in NC, the temperatures don't get THAT cold, and from what I read, that's really the only reason to keep the stock cooler in the loop, so the fluid warms up in cold weather.

 

[440Magnum]

Originally Posted By: Hokiefyd
Do you see a significant drawback to installing an aftermarket ATF cooler and completely bypassing the cooler in the radiator? The OEM setup, even with the additional cooler for towing, runs in series with the cooler in the radiator.

Our MDX has 75,000 miles on it now and it's getting to the point where cooler failure in the radiator is getting more likely. That nearly instantly ruins the transmission. This is an extremely common problem on MDXes and Pilots. Taking the weak internal transmission cooler out of the equation removes the main variable with transmission longevity on the 2004+ MDX/Pilots.

My other option, obviously, is replacing the entire radiator, but that's a more invasive (and costly) procedure that I'd rather not do if I don't have to.

What do you think?


I think its asinine to sell a vehicle that expensive with a transmission cooler that fails before half a million miles. That is just NOT a normal wear/failure item. I've had exactly ONE to develop a problem in the past 33 years of driving (and by the way- that one failure was about 30 years ago in my second well-worn car.)

But I digress... if you run a BIG external cooler, you should be fine. Even in the towing package setups where the coolers are in series, the oil-to-water cooler in the radiator is the one that does the vast majority of the work. Oil-to-water is much more efficient per size of cooler than oil-to-air. Therefore if you replace it completely, you should put in an oil-to-air cooler on the order of 3x to 4x as large as the factory tow-package oil-to-air cooler. A parallel-flow type is much more efficient than a serpentine flow type also.

I wouldn't give a moment's thought to OVER-cooling an automatic transmission anywhere south of the arctic circle. The minute you put the transmission in gear and the torque convertor starts shearing fluid, it begins generating heat and warming the fluid up. Even with a HUGE oil cooler in the dead of winter, the fluid will be moderately warm (at least as warm as when you first start the car in summer) and there should be no problem. Furthermore, in winter the car's own electric fans won't be running much so you won't have as much air flow over that cooler.

One final thought- if you're anticipating that the internal cooler is going to fail AFTER you bypass it, be sure to tightly seal its fittings so that it doesn't dump your coolant all over the highway when it goes. Whatever you do to seal it should be able to tolerate full cooling system pressure + safety margin (I'd say at least 25 psi, given that most radiator caps operate at ~16 PSI. Of course this is a good argument for just replacing the whole [censored] factory radiator with an upgraded aftermarket radiator with tranny cooler.

 

[SuperDave456]

This is actually a common thing on the 2005 Nissan Xterra. The 2004 used a different design, and it is the 2004 my Wife drives.

The 2005 year Nissan used a glue that held the transmission cooler lines inside the radiator that would eventually dissolve in the coolant that came from the factory.
The Nissan Factory fix was to do what you are doing.

You bypass the radiator and get a big cooler.

And you close up the existing cooler line attachments on the radiator (they will go eventually) with either 1 large hose or 2 rubber covers held on with clamps.
A little oil in the coolant shouldn't hurt anything, coolant in your transmission is pretty much instant death.

I'd do some research on your gross vehicle weight, and while you are at it you might want to look into some additional filtration. Either a Spin on full flow oil filter, or a Magnefine. It will add capacity and therefore more cooling capacity.

 

[mechtech2]

You are stuck with a second best solution in this case.
Just run the aftermarket cooler because of a known problem with the radiator's internal one.
But normally, use both, and the aftermarket cooler mfrs also say so.

 

[Hokiefyd]

Thanks guys. It sounds like this isn't unheard of, though it's obviously an issue that shouldn't be there in the first place. Fortunately, a quick fix removes all doubt.

I bought an Imperial Maxi-Kool XL. It's a parallel-flow cooler rated for Class A motorhomes. It was the biggest one they had.

Advance Auto Parts link

And yes, I will plug the old cooler lines in the radiator. I'm sure they'll fail at one point, though the likelihood of that happening without ATF pressure may be reduced.

 

[Towncivilian]

1987-1995 Pathfinders had poorly designed transmission coolers that would clog and kill the transmission, especially if the fluid was not serviced regularly. Many owners opt to bypass the stock cooler and run the largest auxiliary cooler they can, and usually install a filter while they're at it. I'd imagine if the stock cooler was thoroughly cleaned, one could continue using it.

 

[Hokiefyd]

According to this guy's analysis on MDXers.org, it looks like the fittings begin to corrode and leak. It appears to be a problem where the o-rings might not seal correctly, either allowing environmental contaminants (like road salt) one way or engine coolant the other way. Unfortunately, none of this appears to be serviceable in the field, or even inspectable.

Another common theme is this happens more in systems where the coolant may never have been changed. Honda says their extended life coolant is good for 120k miles or 10 years as I recall, but I believe that's insanely over-optimistic...especially the 10 year duration. Our MDX was bought new by my parents, and I know the coolant has not been changed in it. I will do the coolant soon, but am afraid that any hidden damage from time has already been done, if it's even happened at all.

I will proceed with installing the auxilliary cooler now (probably Friday actually), and then if I eventually replace the radiator, I'd likely use the built-in cooler along with the auxilliary cooler.

 

[SuperDave456]

You might want to check out how one would drain and fill the system and go purchase some (Honda?) antifreeze to start flushing the old stuff out of the system.

You are going to be removing body panels and all that mess, might as well kill 2 birds with 1 stone.

 

[RF Overlord]

Hokie, I believe you can buy auxiliary coolers with built-in thermostatic bypass. Might be a few more bux, but will permanently solve your problem.

 

[Hokiefyd]

Some more information, if this is relevant to any other Pilot/Ridgeline/MDX owners on here. The cooler sits inside the bottom of the radiator tank and seals to the inside of the radiator tank with a single o-ring at each connection. Transmission fluid is conveyed from the transmission to the cooler via rubber hoses that clam to two male threaded pipes. These pipes pass through the hole of the radiator tank and into the female threaded connection of the cooler itself. Once tight, they draw the cooler against the wall of the radiator tank and make the seal with the o-ring. There are two washers on the outside of the threaded connection, apparently of dissimilar metals. The theory seems to go that these washers expand and contract at different rates, and also allow corrosion to develop between them. Over time, and as the washers expand and contract, they fatigue the threaded connection and eventually cause the connection to fail, allowing the ATF and coolant to mix. This nearly always results in transmission failure...not a fault of the transmission itself, but of this failed connection in the cooler.

I don't like the design. Alternatives would include putting the male threads on the cooler body, and sliding it through the tank, and having the pipes on the outside have the female threads. That way, even if the same exact fatigue process were to occur, the radiator would simply dump the coolant rather than taking the tranmission with it.

So my plan at this point is to closely inspect the washers used at the two cooler connections for corrosion. Our MDX was rarely used in winter conditions, and was stored for long periods of time in Arizona, which is a terrible place to try to grow rust. If the washers look pristine, I will likely change the coolant now and push off radiator replacement until this spring, when I plan to have the timing belt changed. But if the washers have any signs of corrosion, I'll probably go ahead with radiator replacement now. It appears like it'll be as much work to install the ATF cooler, so I figure I'll just do the job right with an aftermarket radiator, provided I am comfortable that the design has changed so as to eliminate this problem.