Somehow it has escaped my consciousness for years, but I just got smacked with what should have been an obvious question. This is that the revamped hood design placing the intake down at walkway level on "tunnel motors", was to address an overheating problem with the SD45’s, SD40’s & perhaps other road engines. The SD45T-2 enters the scene, and the new design apparently helped or perhaps alleviated the cooling problem. Next, the upgraded SD40, representing much better reliability enters the picture and the SP wants some, but in the T-2 configuration also. So thats what they got. Now, here’s the rub... Why did EMD, apparently with SP’s approval, allow the reduction of cooling system fans by 33 1/3 % (3 to 2) on an engine having 3 fans to begin with?
Obviously, they weren't needed. I'm sure there was some testing to make sure it wouldn't be a problem, but I've seldom, if ever, heard of a 40T-2 overheating in a tunnel and shutting down. The smaller prime mover needed less air movement to keep things cool. Remember, the SD45 prime mover was about a third larger than the SD40's.
The SD45s and SD40s, but with the T-2s, it has a different radiator setup, so 2 fans worked. Looking at the T-2, they could draw in more air vs the standard design, so don't need more fans to move all the air.
So did they just use fans off a GP38-2 or completely redesign a fan mounting bracket that had only 2 holes or did they just leave one of the fans out? If so, which one?
AFAIK, they used the standard EMD 48" 8-blade fan and motor, with the main difference when you peek inside the hood access doors. Instead of a traditional fan housing, the fan/motor assembly is mounted to an air diffuser assembly, which pulls air in from the walkway-level intakes, and pushes it through the roof-mounted radiator cores. This fan arrangement is unique to the T-2s. This is a bit different compared to a traditional EMD cooling arrangement, where the roof-mounted fans are pulling air in through the intakes at the side of the hood roof, and drawing it through the cores. And of course, the SD40T-2 had two of these fan/diffuser assemblies, while the SD45T-2 had three. Again, this is due to the cooling considerations needed for the different engines, the SD45T-2 (20-cylinder) needing more cooling than the SD40T-2 (16-cylinder).
You're right, the GP15s and AC's used the same arrangement. Had SP on the brain and forgot about those other models.
As SP 8299 said, being the fans are pushing air through the radiator instead of pulling it, you won't need as much force.
Intereseting topic. The D&RGW had a similar operating environment and yes, it wasn't only the SD45's and SD40's that were struggling in the long tunnels going up grade. The D&RGW used many 4 axle geeps inluding GP30's GP35's and GP40's on freights in the tunnel district in the Rockies. What they did was to install a radiator spray system, which had tanks of water installed and they could spray water into the radiators when charging through the many tunnels heading up the Front Range. Of course when the tunnel motor option became available to the SD40-2 in 1974, the D&RGW purchased those instead of more SD45's or the standard SD40-2. But apparently the radiator spray systems alieviated the overheating problems sufficiently in the GP units and the SD45's the D&RGW owned and ran. Also, remember at least in the 1970's the D&RGW ran short fast frequent freight trains rather than long slow trains, so that probably made the over heating problem less severe than running long slow slogging freights through tunnels. It seems the overheating problem was mainly an EMD problem as GE had already a walkway level intake as part of their basic design. Since the D&RGW used EMD products exclusively, they had to do something - and of course the SP used GE diesels, but it seems in northern California over Donner Pass (where I grew up), that just wasn't GE territory from some reason, GE diesels were rare if used at all, that was EMD SD45, SD40T-2 and SD45T-2 country, and some SD9's, at least in the 70's and 80's.
I miss the olden days, but I was stuck in the north east in a bad marriage for many years, which may have been a blessing to not watch the decline of the SP in nothern California like a decaying rusting old car. My memories stem mostly from the mid-1970's as a teen into my college years until I moved away in 1983/84 to finish college out of state. The SP was still looking good in Davis, Sacramento and up across Donner pass in those days. In the early 1980's I made some trips to Colorado and discovered a different type of mountain railroading with the D&RGW. Since then I began focusing my modeling efforts toward a Rio Grande Zephyr and D&RGW freight trains. However, since there was a lot of SP power and freight cars feeding from the SP and Pacific northwest across the Rockies, I kind of got my SP fix too! And now with all the nice PC&F freight cars from Athearn and the nice RTR SP tunnel motors and recent shipment of SD45R's, I've been beefing up my HO collection with lots of SP again! Athearn just began shipping their latest run of HO SD45's in the rebuild version (no L wind shield).
