Since diesels tend to be more efficient the hotter the combustion process is, I am thinking wouldn't running intake air from the warm engine compartment be better for efficiency during the winter season?

My 602 takes intake from a grill on the right fender.

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1993 W124 300D 2.5L Turbo, OM602.962
2000 Chevrolet Cavalier, 2.4L DOHC
2002 Ford Explorer, 4.0L SOHC
2005 Toyota Prius, 1.5L

http://www.fuelly.com/sig-us/40601.png

no, regardless cool dense air is better for combustion.

Yep. Hot air intakes work for g@ssers because the lower density means the throttle must be opened further to get the same power output, reducing pumping losses.

Diesels recoup almost all the compression energy on the rebound (combustion) stroke, minus blowby and friction losses, and cooler air burns more efficiently.

Colder air is more dense, thus it has more oxygen available each time the engine draws air.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Well what designer at Mercedes decided to put my air intake right next to my exhaust manifold? What's up with that?

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2007 BMW 328XI