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Interesting points, Ken, have to admit I'm a bit surprised Volvo's setup would position the aux. cooler after the radiator.
Lubricants do their job best within a certain temperature range. For engine oils this is about 180F-220F or so. I would think that ATF would be similar. Having the cooler after the radiator would (certainly on a chilly day) cool below this. As you noted, having it before the rad. removes some of the heat load from the engine cooling system on a hot day with engine/trans working hard, but also, in cool conditions where the trans is not working hard, maintains the fluid at a higher temp than is likely if it's in line after the rad. The trans 'cooler' in the rad's outlet tank will warm up the fluid if it is entering at a temp below the rad's coolant at that point.
As for the rad/coolant making the trans fluid too hot? Doubt it...the trans fluid is more than capable of handling the highest temp the coolant will see. Flash point of ATF is somewhat over 390F. Of course, clutches and seals in the trans don't want to see temps anywhere near that. Coolant might get to 230F exiting the cyl.head under extreme conditions (gauge well into the red). Anyway, the part of the rad where the stock ATF cooler locates is in the outlet tank - after the coolant has been through the entire heat exchanging part of the rad and is ready to re-enter the engine, ie: that's the lowest temp the coolant will show anywhere in the system.
The above theory is all pretty logical to me, but the Volvo engineers aren't dumb (well, maybe the one who placed the heater core where it is) so in the end, you can't go wrong with their instructions.
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Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD; hobbycar 77 MGB, and a few old motorcycles)
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