is this normal 2004 cummins temp drops at idle

I have a 2004 3500 cummins and live in Iowa. in the morning when its 20 or colder it takes abought 15 minutes at hyway speeds so 1900rpms befor the temp comes up to 200 is this slow for diesel?
then when I get to work early and sit in my truck for 5 or 10 minutes befor going in after 5 or so the temp drops at idle to around 160 -170 and the enging revs up to 1000 rpms. should the temp drop like this after engine is warmed up?
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Yes, operating as normal. Diesels do run colder. In very cold weather, you can see radiator covers in use. Steve

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yes, completely normal. in cold weather my wifes '04.5 takes forever to even get "warm" and if idling it will idle all the way back till the temp gauge looks like the truck isnt even running. we'll probably be buying her a gas powered truck soon just so she can get some heat. my '05 warms up quicker, but its pulling a heavy load. it will also cool down at idle.
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