Quote:
Originally Posted by Daox
Yes, EGR coolers on diesel don't necessarily increase mileage (I should have clarified). However, they do allow you to run more EGR. On gas engines the higher amounts of EGR can be used to increase fuel economy by reducing pumping losses and optimize timing.
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Actually EGR coolers on a diesel do improve mileage a tad. Cooler combustion temps mean less heat lost on the combustion stroke to the cooling system. However the sole reason for using them is to meet emissions.
Diesel or not, running more EGR doesn't improve mileage. Running the right amount does.
In a diesel often no egr is best because it allows the turbo to make more pressure in the intake than it uses to drive the turbine in the exhaust.