How long can a diesel locomotive theoretically last?

[es80ac]

How long can diesel locomotive theoretically last given if all the spare parts are available and the owner is willing to do continued major overhauls? I know the locomotive life span is between 15-25 years, but that is kind of vague considering mileage and the type of work is not taken into consideration. What does class I use as metric as to determine when a locomotive should be retired/scrapped? I hope to not get into a GE vs EMD debate as to which one last longer, but in general what would eventually force a engine to retire if overhaul can be done? Is it cracked frame, engine block or etc...? thanks

[DutchRailnut]

engine blocks get replaced all time, but any frame damage will bring end to a locomotive , be it from damage, metal fatigue , rust, etc.
there are locomotives in service of 60 years and better, maybe not in class 1 service , but on short lines and in passenger service.
It really all depends on if owner is still willing to spend money on it or it is part of historical significance.

[MEC407]

Given proper maintenance, and assuming it hasn't been in a wreck severe enough to damage the frame, there's almost no limit on how long they can last. An analogy would be the B52 bombers used by the US military. Those were built in the 1950s and they're still flying today, having been rebuilt multiple times over the years, and the military expects to keep them in service until at least 2040, at which point they'll be close to 90 years old. A railroad could do the same thing with a locomotive if they wanted to. Most railroads, especially Class I railroads, would not do that because it's not efficient or cost effective... but your question was theoretical, so that's the theoretical answer. There are plenty of early GPs and switchers still in daily service which are 60+ years old.

[NorthWest]

The Class One metric is "Is it cheaper to continue to operate it and fix it or buy a replacement?" Once it is more expensive to rebuild and operate a locomotive than to buy a new one, a locomotive will be retired (typically 20-25 years after purchase, but it varies by model and longevity is increasing). In earlier decades financial games with lessors were also a factor, but this is less important now.

As the others have mentioned, the frame is the only thing that can't really be fixed or replaced. Everything else can be in perpetuity, it just may not be cost effective.

[Allen Hazen]

Alco replaced its "High Hood" switcher models with the S1 and S2 in 1940, and I think there are still a few High Hood switchers in (industrial rather than common carrier, but still…) service. So: at least 75 years!

[MEC407]

Plenty of GE "tonners" of that era in service, too.

[mtuandrew]

Yep, fatigue cracks are the killer - after a while, you just can't chase them down anymore, especially the hidden ones that can only be detected via Magnaflux.

That said, early 1950s Geeps, SDs, and SWs are in regular service on Class 1s, with numerous Fs and very early SWs in odd corners. Alcos are less common from that era, mostly S-series locos on Class 3s with a few early RS-series (particularly on the D-L) as well. Baldwins and F-Ms are like hens' teeth, and I have no idea if there are any Lima diesels in use anywhere. It isn't that EMDs are any better built than their contemporaries, but the parts are a dime a dozen.

As for GEs, we already mentioned the industrials as long-lasting - lots from the 40s still roaming around on Class 3s. U-Boats are nearly non-existent though, with a few notable exceptions such as the Pickens, Minnesota Commercial, and former MM&A. GE didn't support the early Universal series as well as it has the Dash-8s and beyond, and I understand they weren't as well built as their contemporaries despite being a match in power. But, the oldest internal-combustion locomotive still in usable shape is GE-built gas-electric Dan Patch #100, so GE fans can take solace in that

[es80ac]

very informative, thank you all. So the frame maybe the key. But about the locomotives that have structures that are load bearing, for example Amtrak Genesis P42 and F units that don't have a main frame but a shell that bears weight. Do these type of locomotives last longer or shorter than let's say a Dash 7 with the regular heavy frame? thanks

[Allen Hazen]

I think most American first generation carbody units (EMD E and F series and comparable models from other builders) were retired for reasons other than worn-out body, so we may not have much evidence about how long they could last in service. However, many British Rail diesel locomotives had truss bodies similar in principle to American "covered wagons," and the Wikipedia article on the BR Class 37 (the last of which were built in 1965) says:
"As of 2015, members of the class are still in mainline service despite most being more than 50 years old."

[Engineer Spike]

CPR has only just retired its GP9 fleet, with the completion of the GP20eco order. The 9s had gone through a major rebuild program in the 1980s.

Sometimes the frame does wear out. There are other factors. The rebuilds had many items modernized. Still it was a very obsolete design. Modern 710 prime mover efficiency and emissions were big factors. The new traction control/wheel slip systems, and better traction motors make the GP20eco a much more capable unit, while still having roughly the same horsepower (+250hp). This makes it possible to have one unit in some cases where two were required with the GP9s.

I'm surprised the 9s lasted so long. One would think that even the rebuilding costs would have been fully amortized.