As an engineer, I'll point out that thermodynamics are thermodynamics, and for a given volume of air passing over the same size radiator, with the same temperature delta, you'll get the same results regardless of where the fan is.
As the Trains blub suggests, there are several variables at work. First what the don't mention: The temperature delta between pulling tunnel roof air (mostly exhaust for the trailing units) versus pulling human head-height air is probably 100F. That's huge in cooling system design terms. That change alone, regardless of fan reconfiguration, is enough to justify all sorts of screwball sheetmetal changes!
At the same time someone in LaGrande undoubtedly improved the fan airflow within the limits of the carbody size. There is, effectively, no airflow difference between a 'pusher' fan and a 'sucker' fan, the differences are in how you constrain the airflow going through the radiator cores.
So all sides are right on this one. Cooling system design is an art form where you have to be aware of a lot of minutia in the design, and ideally take solid in-service measurements to validate the design assumptions because despite advanced airflow modeling it's still a bit of a black art.
SR Krause
Chillicothe, IL
Chris Webster Wrote:
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> Here's a Trains magazine explanation of how the
> tunnel-motor's cooling works:
Quote
Electro-Motive
> Division’s tunnel-motor design, which used low
> air intake vents on the long hood and a cold-side
> radiator fan system. This design places radiator
> fans between the intake and radiators, which push
> a larger volume of cool air through the radiators
> versus a hot-side fan system found on EMD hood
> units that pulls hot air exiting the
> carbody.
> Link, which appears to be available to
> non-subscribers:
>
[url=http://trn.trains.com/railroads/abcs-of-ra
> ilroading/2018/01/tunnel-motors-from-the-past]Tunn
> el (motors) from the past - More than 500 still
> ply the rails, and now there’s a new
> twist[/url][/b]