We have a number of smaller diesels, 5 & 6 cyl. MB's and 7.3 Navistars.
Unless, like the 7.3's, the engines have a warm-up system which raises the idle and uses the turbo to choke the exhaust, a diesel makes VERY little heat while idling.
If they are parked somewhere they cannot be plugged in, they are idled only long enough to get oil pressure up and established then they are driven off slowly until the temp. gauge moves.
Before folks jump up & down. We have tested it both ways, in various temperatures and conditions. A 7.3 will be at running temperature in minutes while gently working. That same engine will not be much more than barely off the end post after idling for 15 or 20 minutes if the cold-idle system isn't activated.
