Pardon me while I step up to my soap box...
The short answer is YES, it’s a design flaw on Honda's part - IMO. I maintain that position based on two realities.
First, the failure mode in question is rooted in well-known, naturally occurring phenomena. Setting aside other (BETTER) aspects of design and implementation, a different choice of material at the mechanical interface of the radiator "could have" resolved this serious – easily avoided galvanic corrosion issue. Perhaps a composite material stable enough to operate in the target environment, or if identical metallurgy in-between and on both sides of the interface were used, this issue would not exist. OEMs are not in the business of building products beyond a limited target reliability range. I would suggest that Honda considered many options - but didn't change direction because anything more than their chosen design wasn’t cost effective and was determined to be… "good enough".
In this case good enough likely meant service life near double the warranty period is plenty good. A certain failure % - both in and out of warranty - are calculated risks to any brand name, so if a "small %" of owners suffer a catastrophic failure during ownership, that's just part of doing business. Since I'm on the receiving end of those BUSINESS decisions, I choose to address them with more seriousness than bean counters do - and seek ways to totally eliminate the possibility of cross contamination of vital fluids - without impacting other serious reliability concerns.
Second, implementation of accepted/conventional designs such as a trans heat exchanger buried inside an engine heat exchanger, doesn’t dismiss the opportunity to innovate. Could Honda accomplish the same thing in a way that avoids a failure allowing coolant and trans fluid to contaminate one another? ABSOLUTELY they could have. Obviously, the "pre-heat" exchanger could have been plumbed in an entirely different way that eliminates all possibility of fluid contamination. I'm positive they considered many alternatives to the final design - I'm equally positive those alternatives were considered cost prohibitive for the overall reliability targets imposed by budget constraints.
In the same way OEMs of internal combustion engines have varying reliability resulting from their implementation decisions - accepted and conventional designs have tons of variables when budgets and target pricing rule the roost. Honda's choice have cost some owners big dollars and inconvenience.
Virtually every product, whether physical or software, has "known bugs" at the time of release to market. Those bugs are addressed and resolved in the aftermarket sector as well as on-going improvements by an OEM - but an OEM has other reasons to invest in those improvements - and almost none of them have to do with improving the user experience - unless of course - there’s risk to the brand name reputation in the marketplace.
Generally speaking, OEM's do a great job of achieving balance in the final product within a price target. As many positive attributes as there are with the RL, this particular short coming is too severe for my personal level of acceptance. "Opinions of others" do have value in the real world and in the context of this issue, there is more than one solution. While it could be argued 3, 5 or 7 year service life with the OEM rad is sufficient, the potential for catastrophe must be calculated by each owner. I'm confident the proposed solution solves the problem – which is 100% elimination of the possibility of fluid contamination and zero impact to engine or trans performance/reliability (in this geographic environment).
As far as “the reported issue being low”, the goal of any proposed solution to an issue is to minimize potential catastrophe. Honda thinks they hit that target when they chose to build the rad/trans cooler as they did, and apparently some forum members agree - but I’d bet real money the folk who took care of their RL’s and saw no signs of trouble yet found themselves on the $h!t end of the stick have a different opinion.
Unknown provenance is the enemy of every used vehicle buyer. Once a new owner of a used RL is aware of this issue - and realizes there is no reliable method to detect a failure that could occur at any time in the future - the only solution becomes preventative maintenance - replacing the rad in a used RL even when it "looks good" and the system operates normally is counter intuitive for some, I imagine. Given the varied experience and quality issues shared by members of this forum, I'm additionally cautious on moving forward with current, off the shelf solutions.
For drivers in this type of climate, I see no downside to this idea. And even in freezing climates, the "damage" caused by flow rates of colder than ideal trans fluid might be less than that of engine lubricant thickened by spending the night at the bottom of a crank case in single digits temps. Obviously, some forum members object to the general idea. Personally, I don’t find fault with questioning certain decisions made by Honda during RL development. Like every OEM, they make a consumer product built for the widest possible range of use scenarios. By definition, that means tradeoffs must be made. This is one of the areas where an OEM tradeoff decision can be remedied without sacrificing reliability in other areas.
But again, that comes from the perspective of almost never having to deal with single digits temperatures.
The 15 year old rad in my 40 year old motor coach gives me confidence with the virtues of an all-aluminum rad. I stuck a scope down its throat about a month ago. She's clean as the day I put her in. <6 Gallons of coolant and distilled water in a closed system works great. BTW: in that application, both engine and trans coolers have pre and post temp sensors and gauges. TMI for some, just right for me as the 100,000 mile 455 Olds/TH425 trans pulls 10,000lbs up long slow grades in the dead of a southern summer. From a service life perspective, an all-aluminum rad would be the last one my RL would ever need - and there is virtually ZERO chance of fluid cross contamination. Problem solved.
As always, to each his own.
Stepping of the box now.
