Diesel locomotive reliability
In Germany and Finland, diesel locomotive hydraulic systems have achieved extremely high reliability in operation. Persistent argument continues over the relative reliability of hydraulic systems, with continuing questions over whether data were manipulated politically to favor local suppliers over German ones.
In the US and Canada, they are now greatly outnumbered by diesel electric locomotives, while they remain dominant in some European countries.
The high reliability of the German diesel locomotives was paralleled by higher reliability of non-German locomotives built with German-made parts compared to that of the same designs built using parts made locally to German patterns under license.
Much of the unreliability experienced outside Germany was due to poor quality control in the local manufacture of engines and transmissions.
Another contributing factor was poor maintenance due to staff accustomed to steam locomotives now working on unfamiliar and much more complex designs in unsuitable conditions, and failing to follow the unit-replacement maintenance methods that were part of the German success.
It is notable that diesel-hydraulic multiple units, with the advantages of modern manufacturing techniques and improved maintenance procedures, are now extremely successful in widespread use, achieving excellent reliability.
Advantages of the diesel hydraulic locomotive
The diesel-hydraulic locomotive has two distinct advantages over the diesel-electric. First, it is lighter for the same power output.
This is particularly important for usage on branch lines allowing only smaller axle loads, which had been the case in Germany for a long time.
Main lines, built for higher axle loads, had already been electrified there, which, was not the case in the US where diesel locomotives were used on main lines as well. Secondly, the factor of adhesion is better, meaning higher starting tractive effort relative to the locomotive weight.
This is because in a diesel-electric all driven axles are driven by individual electric motors and can lose grip individually whereas in a diesel-hydraulic all axles are interconnected by shafts and universal joints.
Thus, all axles must rotate at the same speed, which makes individual slipping of axles impossible. However this second advantage is eliminated if the electric traction motors have anti slip control, a feature often included in modern designs.
In the UK, the Western Region of British Rail bought a number of Diesel-hydraulic locomotives, ranging from small light-duty freight locomotives to high-powered mainline passenger locomotives.
But these were withdrawn early because they were non-standard, and also in some cases suffering from reliability problems, being replaced by diesel-electrics.
A number were rescued for preservation though, and some are capable of running on the mainline.
Diesel locomotive home page