2010 e350 coupe, Had the starter replaced a year ago. Since then, every once in a while, when I try to start the car, I turn the key, the starter engages and I can hear it spin but it doesnt turn over the motor. I detect this in a few seconds and turn the key off and back on to try it again. Usually on the 2nd or sometimes 3rd attempt it will engage the motor and start the car. No other issue, no errors and it doesnt do it all the time. Sometimes it happens when its hot, sometimes cold, sometimes it works fine for a few days. Any ideas what to look for or what to ask a mechanic to check?
Thanks,

 

It sounds like the starter solenoid is not engaging. Starter basically has a solenoid that engages the flexplate on the engine. Starter motor is what turns the engine over. Description you gave describes the starter motor always activates but not so with the solenoid.
Before assuming a starter replacement is needed, a check could be at the connector to the starter. If current always appears from ignition to the solenoid then I'd figure yes time for starter replacement. If current is intermittent I'd look at starter relay and or current from ignition switch itself.
Generally it's a starter issue but just wanted to highlight that verification is good before buying parts.

 

Is the starter, starter relay, and solenoid 3 individual components or is that all made into the starter?
Thanks

 

Starter and solenoid are combined and relay is usually in the underhood fuse box.
Solenoids can sometimes be replaced separately but the starter still needs to be removed. Typically though not worth the hassle, most times the entire unit is replaced.
When you buy a starter it almost always comes with the solenoid.

 

I just replaced my starter.

The starter solenoid mounted to the side of the starter is just a high power relay. It has a heavy duty copper braided wire supplying the direct battery power to the starter motor.

I regret checking on this but i think the engagement of the gears happens with the motor starting to turn and then the inertia of the gear wheel making the helical motor shaft turn in the gear and push it in connection with the flywheel gear.

It seems your gear connection is not happening so you need a new starter.

Edit:
I must take this back as I now think the gear engagement happens thru the solenoid moving the gear but in any case it seems you need a new starter.

 

Is it possible the relay under the hood could cause this or do you feel it is the solenoid on the starter? Since the problem only occurs sometimes, is it more likely an external loose wiring at either of these? The reason I"m asking is that if a solenoid or relay is bad, wouldn't it be defective bad all the time?

Thanks,

 

A relay or solenoid can work intermittently and a poor connection can also contribute to that sometimes-works scenario.

You mentioned that the starter has already been replaced once. Rebuilt or new oem? Sometimes the replacement can have an issue but if that problem started before the starter was replaced and it's now repeating, I'd sure include looking at the wiring voltage/connections/relay before replacing the starter again.

 

Here is crude video of the starter operation:


Order of operation:
1.Solenoid (blue) slides pinion (silver) to engage flex plate (automatic) or flywheel (manual)
2. Once pinion connected to flex plate gear, solenoid turns on (connects two green pins) starter motor.

Based on the post #1 by mdc9966 starter motor is running but engine is not turning over.
In this scenario typical problem is faulty pinion. It supposed to free wheel in one direction only: to make sure that starter is not destroyed once engine has started but key is not yet released from start position. But it supposed to lock up when you turning over the crank with the starter.

Based on the original post is sounds like it is free wheeling in both directions. Or teeth on the flex plate are damaged. The second one is much rarer occurrence.

Max

 

If the starter starts to run every time you try starting the car as you can hear it spinning but sometimes the gears do not engage it means the problem is in the starter. If the starter spinning works every time it means wiring from the battery to starter and from the start relay to starter solenoid are ok.

If the gear engagement in this starter is actuated by starter solenoid then the issue is within the starter solenoid internally as this wiring is internally in the starter solenoid. If engagement is with inertia of the gear wheel then the problem is with that and again internally with the starter.

So, my question is: does the starter start spinning every time you try to start the car?

 

The issue didnt start happening till months after the new starter was installed. It was a new starter, not reman. Its good to know the relay could be an intermittently issue. That will be the easiest to just replace and see if the problem goes away. After that, I will need to take it to the shop. I will inspect for corrosion when I swap out the relay.

 

Everytime the starter motor is spinning. About once a week, give or take a few days, the starter motor spins but it does not engage the flywheel to turn over the motor. This continues unitl i turn off the key at the ignition switch. Usually i can turn the key back to start and it will engage the flywheel and start the car.

If i do not turn off the key, i can hear the starter motor spinning without turning over the engine and this will continue until i turn it off with the ignition switch.

 

So, if the starter spins every time but occasionally does not engage with the flywheel it is not a relay problem. If you had a relay problem your starter would not spin when the starting does not work.

Your problem is internally with the starter motor and as the motor spins it means the issue is with the gear wheel engagement mechanism, likely with the solenoid not moving the gear wheel when you have the problem.

A new starter does not mean it cannot be bad from the beginning, that is why they give warranties for the parts.

 

In older times, it was very common to replace a starter solenoid because the bendix drive was worn or not functioning properly. The bendix drive moves the starter gear into the ring gear on the flywheel, and pulls it out when the ignition key moves from start to run. The return of the drive was via a coil spring that also could be broken/worn.