More problems with KiwiRail's Chinese-made trains have been revealed.
A KiwiRail document obtained by Radio New Zealand said the alternator cooling fan on several DL Locomotives which came into service in the past two years was found to be defective.
Twenty of the locomotives have been put into service and more will soon be added to the fleet.
In one case, cracking to fan blade welds led to the blade breaking away and lodging in protective screens.
Rail staff are warned not to occupy the alternator compartment, or have the doors open to that area, when the engine is on.
KiwiRail says the issue is being rectified by the manufacturer under warranty.
It says the necessary preventative work was quickly completed on all affected locomotives and has not affected freight operations in any way.
However the company has admitted the new Chinese made locomotives are breaking down twice as often as the others in the fleet.
Freight operations general manager Aaron Templeton says there are often teething problems with new rolling stock.
"We believe that DL locomotives are no different to any other locos in that regard."
He says at the moment they are about 50% less reliable than the rest of the fleet, but that is a significant improvement on four or five months ago.
The locomotive problem follows issues with Chinese-made rail wagons, including the brakes on all 500 needing to be replaced before entering service.
KiwiRail said it had carried out work to replace the brakes after initial tests showed fully loaded wagons failed stop within a specified distance.
Mr Templeton said some problems are to be expected when introducing new rolling stock. The the wagons were performing well and had travelled more than 26 million kilometres, he said.
New Zealand First transport spokesperson Brendan Horan says the problems are unacceptable.