Why do diesels knock hard when cold ?

joesmoe3

Well-known member
Joined
Jul 1, 2011
Location
NoVA USA
TDI
2015 Golf TDI SE DSG
My 2011 Jetta sedan, now that the weather is turning cold, when started cold, sounds like a traditional diesel with hard knocking sound until it gets warm, whereupon it returns to the smooth running engine it's been all summer.

I'm just wondering about how a diesel functions, or this diesel in particular functions, that makes it do that ?
 
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