[Huskymaniac]

He got great mileage out of his 1996 which, as we know, had all of the Subaru upgrades. The fact that beefier components helped is not a surprise. And I can rationalize why they may not have put better components in the earlier trannies. Cost. They may have, incorrectly, assumed that the components they had were good enough and when cost pressure mounts, you don't put more expensive components in unless you absolutely have to.

One technique people have used to improve reliability in the older trannies was to open up the passages in the valve body. So my question is, why wouldn't the Subaru engineers have made these passages larger in the first place? It doesn't cost more to make holes bigger. Is there any reason why they wouldn't have wanted these passages to be larger?

The thing that got me to this question was that my 1996 with 89K on it seems to be running quite well. There has been talk recently on what the right type of external cooler is. I noticed on my drive to work today that my TC took about 5-7 minutes to lock up. The temperature outside was 35F and I am running just through the stock cooler in the radiator right now. Most of that time was on "city" roads. Seems to me that my tranny is running quite cool with the stock cooler.

Given that, I would think increasing fluid flow would be more important than improving cooling, assuming that the tranny is in good condition. That has been my assumption all along and it was reinforced today. So an external cooler with lower flow resistance would seem to be a much better choice than a high capacity cooler. In fact, a high capacity cooler may be a negative as it will keep the TC from locking up and degrade fuel efficiency. Therfore, a low capacity cooler with low flow resistance would seem to be the way to go and that points to a small tube and fin cooler.

Once you get past that decision, one then naturally wonders what else would improve flow and line pressure and that brought me back to those valve body modifications. It makes sense with the exception that one has to ask why the Subaru engineers didn't just make the passages larger in the first place. It makes me wonder if there wasn't a logical reason for wanting them smaller.