I think it’s important to have a thermostat.
If it’s -25, as can happen in the mountains, or Vermont, I don’t want that fluid staying too cold because it is constantly flowing through an external oil-air cooler.
My Tundra, for example, has both an oil cooler that exchanges heat with the engine coolant (and thus warms the oil) a big external oil-air transmission cooler, that has a thermostat which opens at about 200. I think they do that for fuel economy (lower viscosity = lower internal drag)
160 would be ideal, I think, but I’ve not found one.
They may be available. Just not easily...
Still, if Toyota thinks 200F is OK, 180F is probably just fine.
Current Fleet:
2016 Tundra Crewmax 4WD 1794
2005 MB S600 (126K, Michelin AS4, HPL 0W40)
2005 MB SL600 (55K Michelin AS4, Mobil 1 0W40)
2004 V70R (143K, six speed M66, HPL 5W40)
2004 XC90 (235K, HPL 0W30 Euro)
2002 V70-XC (295K, HPL 0W30 Euro)
2002 V70-T5 (225K, IPD bars, Bilsteins)
2001 V70-T5 (125K, IPD downpipe, cat back and other mods)
1932 Packard Sedan (straight 8, dual sidemounts, original paint and interior, Shell Rotella 15W40)
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