Originally Posted by Astro14
If you don't want to cool it too much, then add the thermostat. Is total cost a big concern? You can do a thermostat, remote filter, and new plate-type cooler for about $150 in parts. Bypass the factory system, make changing the filter much simpler, and increase cooling.
Here's a write-up on how I modified my Volvo - note that I've done all three of them the same way, just have pictures from the first one. Now, in my case, I wasn't worried about contamination, so I left the factory radiator cooling loop in place. You could easily delete that loop to allay your concerns.
https://www.volvoxc.com/forums/showthread.php?27334-02-XC70-Transmission-Flush-From-Bottom/page2
I should add that this transmission is known for failing in Volvos of this year. I've got over 258,000 on the XC-70 on the original transmission. I contend that longevity is due to better cooling and reasonable fluid changes.
Based on Astro's post in the xcvolvo forum I installed the Volvo OE Setrab remote AT cooler in the 240 wagon. Normally the AT fluid cools only in the radiator. Volvo didn't include a thermostat with the remote AT cooler. Apparently they didn't feel one was necessary.
I use this car primarily for long distance trips in the summer. It's heavily loaded with 2 mountain bikes, a rocket box, an awning, gear, luggage and people.
The decrease in coolant temps was immediately apparent. During cruise or climbing the coolant temps were lower than the similar trip the previous summer. The highest AT temp was 187 degrees, recorded at the top of Mt Lemmon in Tucson - a 36 mile climb.
I concur with Astro that regular fluid changes and lower fluid temps should help the unit last a long time.
An interesting side note concerning the lack of a thermostat. I purchased the cooler from a Volvo 240 enthusiast who lives in Nenana Alaska. He had it on an 89 240 - his daily driver back and forth work in Fairbanks and Anchorage. He never bothered to add a thermostat and said the tranny shifted perfectly. He got tired of the automatic and swapped a manual in its place.