Pass Fail on starter motor test

[tron9000]

I have a relative that works in a garage, she recently sent back a new starter motor that didn't work when fitted to a vehicle. Another motor was found and fitted and the car now starts.

A test report on the duff motor was emailed and came back to her as working, all test criteria were within spec but all on the bottom limit. Especially the starter solenoid current: the reading was 31.8mA, but the fail limit was 31mA.

The motor was tested by Bosch or a distributor under Bosch. I assume they have a full test lab and would definitely have some decent kit and some experienced and capable employees to boot.

Out of interest, I asked if she could ask them what kit they are using to test the current with and how they are measuring the current (inline? clamp meter?) - I'm expecting a decent bench meter and inline.

But 31.8mA out of a 31mA fail limit?

...would anyone else want a second reading or opinion on that if it was you testing it?

[flynwill]

What was the nature of the failure of the new starter?  Did the solenoid fail to pull in?  Hard to tell what went wrong, but solenoid current being close to the lower limit is a pretty unlikely candidate.

[mikerj]

I have a relative that works in a garage, she recently sent back a new starter motor that didn't work when fitted to a vehicle. Another motor was found and fitted and the car now starts.

A test report on the duff motor was emailed and came back to her as working, all test criteria were within spec but all on the bottom limit. Especially the starter solenoid current: the reading was 31.8mA, but the fail limit was 31mA.

That sounds at least two orders of magnitude too low for a starter solenoid.  They typically take around 10 amps or so.

[SeanB]

I would bet the starter sent back had been in storage for a while, and had built up a film on either the solenoid contacts or on the motor brushes, preventing current from flowing through the motor.  The vibration from transport or the turning of the motor shaft would have likely removed the film and thus it passed, or the connector on the car side had corrosion, and the wiping of the contact on the removal and reinsertion cleaned it up enough to get it working again.

If it is a VAG vehicle the ignition switch could also be faulty. There are a lot of recalls for those switches, I just had my one replaced ( as the steering column had to come out to get the clutch pedal assembly out so making it easy) and there have been a few batches with either poor starting issues or catching fire.

[G7PSK]

Testing of starter motors is usually done on a special test rig that puts a predetermined load on the starter motor, at least this is the case at all the places I have been to to either get a starter repaired, exchanged or a new one the same goes for alternators as well.

[tron9000]

What was the nature of the failure of the new starter?  Did the solenoid fail to pull in?  Hard to tell what went wrong, but solenoid current being close to the lower limit is a pretty unlikely candidate.

Well its a garage with the simple work mantra of: its busted, replace it and move on! So there was likely no further diagnostic by the mechanic.

That sounds at least two orders of magnitude too low for a starter solenoid.  They typically take around 10 amps or so.

I'm pretty sure she said solenoid current. Will double check.

I would bet the starter sent back had been in storage for a while, and had built up a film on either the solenoid contacts or on the motor brushes, preventing current from flowing through the motor.  The vibration from transport or the turning of the motor shaft would have likely removed the film and thus it passed, or the connector on the car side had corrosion, and the wiping of the contact on the removal and reinsertion cleaned it up enough to get it working again.

If it is a VAG vehicle the ignition switch could also be faulty. There are a lot of recalls for those switches, I just had my one replaced ( as the steering column had to come out to get the clutch pedal assembly out so making it easy) and there have been a few batches with either poor starting issues or catching fire.

It's a ford garage. - but thanks for the info, we have a VW Passat, so will keep an eye out for that one if it packs in (and hopefully doesn't catch fire!)

That does sound like a likely and plausible cause though from a very typical situation.
 

Testing of starter motors is usually done on a special test rig that puts a predetermined load on the starter motor, at least this is the case at all the places I have been to to either get a starter repaired, exchanged or a new one the same goes for alternators as well.

Oddly enough one of the tests that came back was "unloaded spindle speed" and "unloaded current".

Cheers for the replys!