I recently got a job that requires driving lots of short trips throughout the day. Drive for 10 minutes park for 20. (I do water testing for an environmental firm. So don't get any ideas) I am wondering if this type of driving is bad for my 85 300td turbo. Is it better to let it idle? Should I drive my Volvo gasser? How much warm up and cool down time do I need if the car has only been siting for 20-30 minutes?

I wouldn't worry about anything, but I would change the oil more often. Idling just wastes fuel, for no real gains.

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes

Hm. Well if you get it all warmed up before you drive for 10 minutes and leave it for 20 minutes theres no issues... but if the engine's cold and you park it after driving for 10 minutes I would change the oil more often than 3K miles. If it is all warmed up though all you are doing is putting more wear on the starter. They are tough though, and when everything's warmed up it shouldnt take a crank or two to get the engine going.

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1985 CA 300D Turbo , 213K mi

I'm no expert, but I suggest you use a cleaner additive like Diesel Service mixed with Marvel Mystery Oil nevery other tankful, and also take the car for a run on the highway at 65-75 MPH every couple of weeks to keep it cleaned out. My 1984 with about 240k feels a lot better when I do that after running around town on errends for a few days.

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rdsw
Salem, NH
1984 300SD, 260k miles and counting