This came up today in discussion with a tourist railroad, and is shared here for information in the event that it might be useful to any RYPN participants:

EMD GP7 AND GP9 FAN SEQUENCING NOTES

Original GP7 Fan Sequence is 1-3-4-2

#1 Fan 165 Degrees, shutters were originally manual operation
#3 Fan 168 Degrees, shutters remain closed
#4 Fan 171 Degrees, shutters open for #3 and #4 fans
#2 Fan 180 Degrees, shutters open for #2 fan
High Temperature Alarm is 208 degrees


One Early GP9 Fan Sequence 4-2-3-1 (Different from GP7)

#4 Fan 165 Degrees, shutters remain closed
#2 Fan 168 Degrees, shutters remain closed
#3 Fan 171 Degrees, shutters open for #3 and #4 fans
#1 Fan 180 Degrees, shutters open for #1 and #2 fans
High Temperature Alarm is 208 degrees


Later GP9 Sequence 3-2-1-4 (Units Built After 24 Dec. 1955)

#3 Fan 170 Degrees, shutters remain closed
#2 Fan 174 Degrees, shutters open for #1 and #2 fans
#1 Fan 178 Degrees, no shutter change
#4 Fan 182 Degrees, shutters open for #3 and #4 fans
High Temperature Alarm is 208 degrees

Tolerance on pickup temperatures: +/- 1 degree
Dropout temperatures generally 10 degrees less than pickup
Tolerance on dropout temperatures +/- 2 degrees

There may be more variations.

Many units have a switch to manually cut out the operation of one cooling fan for winter operation.

References:
EMD GP7 Operating Manual
EMD GP9 Operating Manual
GMDL GP9 Operating Manual
EMD Pointers - 13 September 1956 – Page 2

PC

Seems to me that one fan will be replaced on a regular basis while another one will last and last and last.

Early F3 units had a sequencing switch so that a different fan would start up first, EMD determined that the fans were reliable enough and the switch was a maintenance headache so they did away with it.
Mike Tillger

There was (is?) at least one aftermarket supplier who supplied a fan controller that would alternate the cooling fan start sequence.

Dave

Yes Dave, that unit was still on the market the last time I checked, and handles up to four cooling fans so it could be adapted to a GP7 or GP9.

I helped with maintaining a fleet of F40PHM units equipped with them, and they worked well.

That is just an observation, I am not endorsing any products here.

It is called "Smart Series Locomotive Cooling System Control". That description will be adequate to locate the manufacturer on most internet search services. It is an aftermarket product, not EMD, and is not mentioned in EMD publications.

PC

Why would it run fans if the shutters are closed? Is there intentional leakage?


Asymmetrical wear is potentially a desirable thing. An example is an ETOPS aircraft.

Any system you built to distribute the task more evenly, would distribute it perfectly evenly in an era without the smarts of microcontrollers to plan randomness. Which means all fans would be the same age and runtime. But if all fans are at the same life-cycle point, it greatly increases the odds of a unit with a fan failure having a second one, at which point you have a disruptive, non-planned maintenance event.

Yes, there is intentional leakage, reversed flow actually. On pairs of fans in the same compartment, where the first one starting does not open the shutters, it pulls air around the baffles and through the radiator inlet chamber and backdrafts the second fan. Max Ephraim may have intended that the first fan have a different effective BTU rate than the second one. It is also a way to help prevent the 2nd fan and the shutter mechanism from getting ice-stuck in winter weather. If this were 1974 I would ask Max about the fan control logic at lunch time, as he had been project engineer for these locomotives. He passed away in 2001.

The same logic is used in controlling the two fans of a GP38. The first fan starts and backdrafts the second fan through the combined inlet chamber, then with increasing water temperature the 2nd fan starts and simultaneously opens the shutters.

PC