Do bad glow plugs effect mileage?

Brock_from_WI

Veteran Member
Joined
Sep 19, 2002
Location
Green Bay, WI USA
TDI
2003 wagon
Again on my 03 wagon with a manual transmission the regular glow plugs don't come on above about 40F. HOWEVER the coolant glow plugs come on when I start whenever the coolant temp is below about 100F. So when I leave work in the summer at 75F, they come on. They only run for a few minutes, but they are on. Again if you have an auto it doesn't have coolant glow plugs.

Whether this is for emissions for just getting the engine up to temp could be an argument, but in the end the results are the same.
 
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