Does my '91 turbo have an air box thermostat, or is that only on NA cars? The FAQ on this subject aren't quite clear as to whether turbocharged engines have one or not. Thanks.
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Darius in Albany NY '86 744 GLE (175K, given to my mother-in-law); '91 745 Turbo (167K-my "Little Red Wagon"))

My '87 740T(California) has one, my '90 760T(49 state) doesn't, so I'd guess yours doesn't, too.
If there's a ~2" diameter silver hose running from the exhaust pipe to the airbox, you've got one.
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Jim McDonald

My 89 740 turbo has it. Maybe with the switch from LH2.2 to LH2.4 they got rid of it for turbos.

My engine temp does warm up very quickly - nice in winter.
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Paul NW Indiana '89 740 Turbo 110,000

I wonder if they took it off on later models, my '85 740 Turbo has one. It's easy to tell if you have one or not. There would be a big metallic hose from the exaust side of the engine going up to the bottom of the air filter box. Mine had failed in the open position just like it talks about in the FAQ. I would never have known the thing was in there. There's lots of helpful info here.

Turbos do not have airbox thermostats. The compression action of the turbo itself is adequate to heat incoming air, which is then cooled in the intercooler.