What model are we talking about?

My turbocharged 300D handles altitude pretty well until you get it over 10,000 feet. My non-turbo 240D made it over 8,000 foot passes, but was down on power. I never got either car up high enough to not start, and I've never done anything special for high altitude, but I only live at 4,700 feet, and seldom go any higher than Mt. Rose Summit (a little under 9,000).

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.