You don't really want to know how cold it is leigh! :lol:
Anyway, one of these has been telling me just how brass monkey it has been for the last couple of days. It's not waterproof, but all I did was cover all the holes in its case with five minute epoxy and it's held up for the last year or so without any problems Outdoor Car Thermometer on this page
It's 12v powered so no batteries to replace, but there is a bit of plumbing in needed if you don't want to have the cable to the power socket floating around. The probe lives in the left indicator (knew there was a reason the 01's had them on stalks) so it's out of the hot air from the engine.
However, they are lying when they say it has a strong backlight :evil: a slightly hungover gloworm would be more effective.
Seem to recall seeing a temp gauge designed to go on a bike in one of the accessory catalogues, possibly Hein Gericke, but had no more luck tracking it down than you. Wasn't there a thread about this on the old site?