At the expense of a long, boring post, with no direct connection to the MDX, and lots of pointless detail on Q45 transmissions, I am excerpting text from a conversation with a expert on transmission service:
Why Transmissions Fail
"Gil: Any trans that has a forward clutch that releases when 4th engages will have the problem of the rings shrinking or wearing out. Almost all the Japanese transmissions have this problem, and when it happens it is just as likely that the trans will come in with a planet failure, or forward clutch slip on startoff or during the shift to 3rd, or no 3rd hot or slip to 3rd. Dennis: Is there any one thing that you see as a reason why a major repair doesn't go as far as the original trans? Gil: If I can only name one it would be the radiator. Testing has shown that a high-miles radiator increases trans temperature 0 to 70 degrees. Dennis: Is this because the tubes slowly plug up? Gil:
No. Even with the tubes all open they don't transfer heat like a new one. They gradually scale up inside and out and the scale acts as an insulator. Dennis: Would sending the radiator out to be cleaned help it? Gil: Not enough to matter. The only fix is a new radiator or installing an ample size auxiliary cooler. Dennis: Does the higher temperature actually burn up the friction material? Gil: No. Mostly the higher temperature shrinks or deforms the rings and seals. Then the feed circuit leaks, allows slippage, which then burns up the friction units. Or ring crossleaks into or out of the lube circuit cause gear train burnup.
Dennis: So this would happen even if the vehicle got a brand new trans. Gil: Exactly, and it does. Dennis: Can you give an example of this? Gil: Yes. A Q45 is a great example. From new this car takes 4 people to Las Vegas from Orange County about once a week. On the Baker upgrade the converter unlocks, in 4th, and the trans temp goes to about 220ø .
If you took the trans apart you would find the end gap on the rear support rings is zero to 0.012". 4 years and 62,000 miles later the radiator is no longer new. And on one hot July day the temp goes to 240ø for about ten minutes. The rings now shrink and have a 0.035" gap. Feed for forward or coast crossleaks into the lube circuit and opposes the flow coming from the cooler. Soon there is little or no flow through the cooler. When trans temp gets to 280ø on a pull in fourth gear, the front planetary exits the trans. A major repair on the trans fails on the next hot trip. In fact, sometimes the job will eat the planet on the way home. Lots of shops have had this experience. After three repairs the owner is disgusted and goes to the dealer and buys a new trans. On the 2nd trip in July it burns up the planet. By this time somebody is more than willing to install a new radiator. What we say is: "install a big auxiliary multitube cooler for one fifth the money and 4 hours quicker."
Dennis: So what you are saying is that the higher fluid temperature doesn't burn up the trans
directly, but it causes ring and seal malfunctions that then cause the failure. Gil: That's it, and the solution is twofold. (1) reduce the fluid temperature by improving cooling, and (2) install rings and seals that can withstand higher temperatures and resist shrinking or deforming. Dennis: Is this why some shops pay up to $122 dollars for the original OE rings when repairing a RE4R01As, 2As, and 3As and some of the other Japanese transmissions? Gil: Yes. Those rings are a very special material and are literally bulletproof, provided the temperature stays within reason. But the shop should bear in mind that if the trans got hot enough to shrink the original rings, just like the Q45 did at least twice, the same new rings will also shrink unless serious cooling is added.
Personal experience: I fried two trans- now I installed an aux cooling radiator prior to the third.. Install yours BEFORE summer. No comments on additives- "Lubeguard" has been reported to help keep trans clean.
NOTE- It is NOT the fluid that breaks down at high temp, but the seals- so what does a hi-temp additive do to help?
Is this directly applicable to the MDX/Acura transmission? Don't know. Does it seem prudent? Yep
Ard