Maintenance, Troubleshooting


After spending nearly two weeks at Mercedes-Benz, we finally picked up our 2015 Roadtrek E-trek late Thursday afternoon, August 20th. In our post titled Finally Some Answers–Part I, we detailed the first replacement of the serpentine belt which must have come off the pulleys (and subsequently shredded) sometime in May. After that belt replacement, we tested the battery charging system to confirm that it was working, which it seemed to be. We logged the results in our Etrek Battery Log–June.

We didn’t take any trips to speak of until the first weekend in August, when we drove up to visit our son at camp. Something must have happened on that trip, because when we got home, we noticed that battery strength %/Volts had not gone up considering the 1 hour, 50-mile highway-speed drive. We continued testing the week of August 3rd, but the battery did not appear to be charging by idling or driving. When Karl (finally) checked under the hood, it appeared that the belt had slipped off again. We brought it back to Mercedes-Benz that afternoon (Friday, August 7th).

The same service technician performed the investigation, and determined that a [belt tensioner] bolt had come off, and that a new belt tensioner and alternator pulley would need to be ordered from Roadtrek since this was related to the secondary alternator, a Roadtrek modification which allows the batteries to be charged by the under-hood generator.

The correct parts were received on Tuesday, August 18th, and the work was completed August 19th. In the meantime, the service technician had also changed the oil. Roadtrek coordinated payment of the service, even including the oil change, so everything was settled by Thursday. In both instances the Roadtrek service team worked well with Mercedes-Benz to provide parts and cover the warranty service.

Now, you may wondering why the oil change was performed since we had driven only 4,519 miles–far short of the 20,000 mile service reminder. Karl had asked the Service technician for his opinion on whether or not performing an engine oil change every 20,000 miles was reasonable. The technician said that since the Sprinter with the coach was very heavy, we should change the engine oil much more frequently (~7,000 miles) to prevent damage to the engine. Furthermore, since the cooling fan had not been working due to the belt failure, the engine overheated on our trip home from Boston (see our post Trip #6–Part II) and we were concerned that this impacted the quality of the oil. Therefore, not wanting to be back at MB in two months (when we expect to reach 7,000 miles), Karl had the engine oil changed.

Upon leaving the service center, the battery was at 80%/24 Volts. We started and revved the engine for a few seconds to above 2,500 RPM (to “excite” the under-hood generator); however, the inverter display only went to 90%/25 Volts, not 100%/27 Volts, as we expected. Upon arriving home, and turning off the engine, the battery was at 94%/26 Volts, in other words, fully charged, so we believed the batteries were charging. However, we were still perplexed as to why the inverter display only went to 90%/25 Volts when we started the engine at Mercedes-Benz. We parked the E-trek and turned everything (battery disconnect, Inverter, and Webasto) off.

The next morning (Friday, August 21st), the battery was at 84%/25 Volts. We sent an e-mail to Roadtrek with our follow-up questions regarding the inverter display during charging. Later in the day on Friday, we received a call from one of Roadtrek’s service technicians to address our concerns.  According to the E-trek expert at Roadtrek, if the inverter display indicates a “moderately depleted” level % (e.g., 80%), it will jump up immediately upon “exciting” the under-hood generator, but not necessarily to 100%. We had thought that at any battery charge level, the inverter display would read 100% after the under-hood generator was “excited,” but that is not the case, according to the Roadtrek technician. However, the inverter will always read 100% when charging by plugging into shore power. The Roadtrek technician also confirmed that the small white dial (see picture below), on the inverter should be set at “5” to allow maximum battery output.


On Saturday, August 22nd, we performed an idling test. At 1:00 p.m., (everything still off) the battery was at 88%/25 Volts. We started and revved the engine, and the battery display went to 100%/27 Volts as expected (phew!). An hour later we stopped the engine, and checked the battery which was at 94%/26 Volts. We are satisfied that the batteries are now charging properly by driving and idling. All of the results for our recent testing have been logged in Etrek Battery Log–August.

Of course, our true test will be this weekend, when we take our son back to college in Boston–stay tuned!

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