303.5E vs 305.5E2 vs PC35MR: Which 3.5-Ton Mini Excavator Survives 6,000 Hours Without Major Repair?
The PC35MR? In all honesty, it didn’t appear to be very exciting. The pump was clean. Oil was NOT brown in color. Filter element had normal metallic fuzz–as you would expect after break in–no chunks, and no glitter. At 20MPa, case drain flow was 1.4L/min which was well within the specification. The seals appeared to be virtually new. I removed this swashplate and ran my finger over this thrust surface—smooth. No radial grooves. No heat discoloration. However, here is the issue; Komatsu rates this pump at 23.5 MPa max system pressure as opposed to 24.5 MPa pressure on the Cat pumps. 1 MPa difference seems to be nothing. It’s everything.
Data sources for the table above:https://www.heavyequipmentforums.com/threads/komatsu-pc27r-8-hydraulic-problem.121543/
The hydraulic oil temperature kept its head above water in the PC35MR, being 11-14°C cooler than in the Cat in the same situation. I had a thermal camera on both machines for that week and was able to see the difference in the return line temperature, immediately after the control valve. The colder the oil the longer the life (longevity) will be of the seals, the less oxidative breakdown of the oil, and the less thermal stress on all the elastomers in the system. I can attest to the validity of the latter by the fact that I pulled down the same pump later that had those same seals and they were in pretty good shape, they would have been able to run another 4,000 hours when I was in the process of pulling them out.
In fact, that is why rental companies adore the PC35MR to rent for light duty jobs and landscape applications. The less expensive it is per hour the better margin it will give. However, if the machine is going to a contractor that is a heavy trencher or demo supporting type, then it’s a Cat machine since the cost delta on the undercarriage is negligible to the productivity gain.
Again, it’s always the same… it depends on what you do with it. As that may sound a cop-out but it isn’t. These machines have been designed for various purposes and if you get your duty cycle wrong, you will pay the price.
For Utility work, Water, Sewer, Telecom Drops or any other type of work that is trenching for several hours a day in varying soil I would use the 305.5E2. The hydraulic pressure headroom brings added force for getting through rough spots without being forced to “lug the engine” and the eight-roller undercarriage provides better load distribution than any 303.5E when running continually in rough terrain. Yes, the seals on the pump will be replaced sooner than on the Komatsu. Yes, the case drain flow will slowly increase after 5,000 hours at a level of above 3 L/min. However, if you’re charging on a linear foot or by the job the productivity increase is worthwhile.
For use with fine grading, landscaping or any other application that requires spending the majority of the day on part throttle, low loads then the PC35MR is very clearly the choice to make. The savings on parts (parts cost per hour) due to the lower system pressure and better undercarriage, and the productivity loss isn’t significant due to not pushing the hydraulics system to the max. There is an acquaintance of mine that has 4 of the PC35MR’s engaged in residential grading here in Colorado.
If you are a one man band and you can’t afford down time. The hydraulic system’s conservatism and longevity in the undercarriage equates to fewer unforeseen failures and as the guy turning the wrench, that’s more valuable than what any spec sheet can offer.
