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Old 04-03-2012, 11:28 PM   #26 (permalink)
Diesel_Dave
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There's a variety of diesel technology out there and it's important to distinguish between the different technoologies. First off, let's cover the turbo issues. Historically, turbos were fixed geometry/wastgated and used only oil to cool them. The issue with a hot shutdown there is that when the engine stops so does the oil flow, so the oil near the hot metal of the turbo can coke up. This is because of all the heat that's stil in the metal of the turbo and the fact that oil won't thermal siphon very well. Many modern diesels (but not all) have variable geometry turbos with electronics attached. The electronics require much more cooling, thus engine coolant is used for cooling in addition to oil. The coolant won't coke up like the oil will, and will also thermal siphon so that the oil doesn't coke. So hot shutdowns with oil-cooled turbos are a no-no, whereas it's fine for one with coolant cooling.

Now, as far as aftertreatment goes, this varies greatly with the specifc engine. Whether you have EGR, SCR, DPF, NOx adsorbor, etc. The tuning is also very different for different applications. In some cases almost all the DPF regenerations are done "passively", i.e. no extra fuel required. In other cases "active" regenerations are required. Some applications also have special "warm up" modes that they'l go into to keep the SCR warm, and/or do a DPF regen. It's impossible to make a blanket statement the "Modern diesels all work this way..."
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Diesel Dave

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1 Year Avg (Every Mile Traveled) = 47.8 mpg

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