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"… pushing the limits!"

Gradients of 100%, altitudes of 1,500 m, tree trunks over a metre thick: how PHI OIL has managed to extend the capabilities of a stump grinder.


Steinwendner Agrar Service GmbH


The grinding of tree stumps is one of the toughest jobs a hydraulic system will have to handle. Specifically, the stump grinder was being used on extreme slopes with gradients of up to 100% (45°). Continuous operation in such extreme cases means that machines such as these are operating at the limit of their capabilities.


The use of hydraulic oils recommended by the manufacturer was causing actual damage. The lubricants being used were inadequate and thus incapable of sufficiently protecting the hydraulic components in such extreme conditions. The first incident of damage to the power train occurred after 1,300 operating hours. During the first 2,700 operating hours (3 years), motors, drive pumps and final drives had to be replaced.


Replacement of the entire drive assembly and switch to PHI OIL Universus Gold 5W40

Machine & function
Stump grinder with caterpillar drive, manufacturer/type: AHWI RT 400, power: 402 PS, 6 cylinder, 12 litre capacity, 20 tonne total weight, used to grind logs on extremely steep slopes.

Affected unit
Hydraulic system


Since replacing the drive assembly and switching to PHI OIL there has been no further damage to the hydraulic systems. The unit has since been in operation for a further 3,200 hours without incident. After 1,000 operating hours a used oil analysis is always carried out, and an oil change takes place after 2,000 operating hours. Despite extreme demands, the stump grinder is capable of rising to the challenge without any problems whatsoever.

Client testimonial

The stump grinder was always a real headache. Every few hundred hours a hydraulic component would fail. PHI OIL were then recommended to us. After a very competent consultation, PHI OIL helped us put together a lubrication concept which is simple and which reduces the stress on the components. We have since had no further damage to our stump grinder. By using Universus Gold 5W40 we have been able to cut expected costs by around EUR 22 per operating hour. Furthermore, working with PHI OIL has given us a very thorough understanding of the interaction between machines and oil and now we know our equipment better than ever. Had these problems continued, our maintenance costs, with downtime, would have been about EUR 60,000 higher over the last 3 years of operation!

Thomas Steinwendner, CEO, Steinwendner Agrar Service GmbH


Note: The photos do not show the affected AHWI RT 400 but the AHWI Raptor 800, which was provided for a test.

Video - Making of

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