Sprinter Starter Repair

My Roadtrek CS Adventurous is over three years old, and I'm starting to get a few things that let be know it's not showroom new anymore. A couple of weeks ago I had a slow crank (motor turns over slowly, but eventually starts) on the way to Gamble Rogers State Recreation Area.  When we got there a couple of hours later, I turned the van off to go in and register, and it wouldn't turn over at all when I got back into it. I fiddled with all my switches (one of my coach battery banks is tied in with the chassis battery that powers the starter) and it started up a couple of minutes later, but there was a strong hot electrical smell under the hood. It started fine on the way home and afterward, but I was worried.

Out in the middle of nowhere.

I don't want this starting problem to come back when I'm out in the middle of nowhere. And when I say “the middle of nowhere”, I mean 100 miles to the nearest grocery store, like Big Bend National Park.  We need reliability because we camp often in remote, barely accessible areas, and the javelinas won't sell you the auto parts you need to get rolling again. What I do is try to do preventative maintenance when I'm driveway camping for the winter so that I'll have an uneventful year out on the road.

I had a trip to the Mercedes dealership scheduled for unrelated stuff anyway, and while they had it I described the problem and told them to look for signs of violence. The starter circuit is hundreds of amps, and whatever the resistance that causes the problem should be easy to find if it's a connection. The starter circuit is mind-numbingly simple – power goes from the battery to the starter, and back to the battery through the engine-to-chassis ground. They can get it up on a lift and see everything, which I can't do as a shadetree mechanic, but they couldn't find any connections that looked like they got cooked. The battery tested out fine as well, which I suspected it would because my voltmeter didn't show any alarmingly low numbers during the slow crank/no crank episode.

These starters are surprisingly small – about the diameter of a can of beans. Weight saving and modern efficiency.

OK, the wires and battery are fine, which leaves one suspect – the starter itself. I find one online for $170, brand new OEM (Mercedes uses Bosch starters), but 60% of the price you'd pay at a Mercedes dealership. That's why I'll pay a dealership to diagnose the problem, but not to fix it. They mark parts made by independent suppliers like they're some luxury item, and the old mechanic in me gets rubbed the wrong way by that practice. Two days later, here comes my new starter, and it's time to get dirty.

Up in the air – a foot, anyway. Good thing I'm skinny.

I need to get the van a foot off the ground or so, and my sister has some 2000 pound rated ramps. I pull out my data with the weights we got when we weighed my unit to make the yellow door sticker – 1800 pounts left front, 1740 right front.  Pretty close to the weight limits on these ramps. I put a bunch of bricks under the ramps so if they start sagging the bricks will take the weight, and generously sprinkle jack stands around supporting the frame before I gingerly get underneath. I have lived through many decades of automotive maintenance risk – don't want to make a mistake now.

Starters are easy – two bolts, two wires. Except of course, it's a Mercedes and all the fasteners are E-Torx special heads on the bolts. I need a set of E-Torx sockets. Since the van warranty is gone, I figured I'll be getting a lot of use out of these, and picked up a set at the local auto parts store. Off comes the old starter, I thread the new one into position, bolt it up… and now I can't find the solenoid wire I disconnected from the old starter. Back off comes the new starter, and sure enough, I had managed to leave the solenoid wire jammed between the starter and the engine. This is what happens when you're out of practice. Then I start dropping the nuts which hold the  solenoid wire on into the transverse member, which eats them. WAY out of practice. Luckily, my junk drawer collection of fasteners that I haul around everywhere with me provides a suitable replacement.  I crank it up, get it off the ramps, and I'm done in a couple of hours… on a job that pays maybe 45 minutes flat rate. If I were still working as a mechnic, I'd starve to death.

Solenoid. The larger post on the top right shows signs of being fried, and is also a bit loose. The battery cable itself looked fine – the problem is internal. Terminal 30 is always unswitched positive in Boschese.  Small connection at 6 o'clock is for the solenoid wire.

Now for the autopsy on the old starter. Sure enough, the stud where the battery wire connects looks a little fried, and is wobbly. I sniff, and there's that acrid electrical smell I remember from Gamble Rogers. The solenoid is the culprit. It's an electromagnetic relay that pulls the high-amperage contacts together and moves the starter drive gear forward into the flywheel to turn the moter over, and is activated by the wire from the starter switch, so you don't have to run all that current through your ignition switch. The high-amperage connection was wonky, got hot, and welded itself a new surface, which is why it started working again. Now I know that I have found the problem, and with a new starter I know that this problem isn't lurking somewhere waiting to come back at an inopportune time.  Starters usually last much longer that this, but I have very little tolerance for starter/battery problems. It doesn't take much to convince me to replace them, because with my luck they'll strand me somewhere I don't want to be stranded. $170 is a good price to pay for peace of mind.