I while back I saw an older article (see link below) stating that engine wear increases rapidly at temperatures under 170 F (77 C). What I think is the most damaging to an engine is cold start owing to the pistons expanding faster than the cylinders. I always try to get my engine to temperature a.s.a.p. without revving it over 2500 rpm or so. Also, I believe synthetic oil goes a long way in reducing wear during cold starts. Quite frankly I'm more concerned about hot running engines than cold running ones.

http://www.gi.alaska.edu/ScienceForum/ASF7/747.html

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Reno

'93 300E 4Matic
'98 Nissan Altima
'00 Yamaha Road Star Silverado