[Cowiepeters]

The domestic goddess's ML500 (Australia) has 110,000km, she has had it for 3 years from 80,000km

Great car, no major issues except I replaced the rear airmatic bags at about 100,000km when one developed a leak

The engine has generally been slow to crank since she got it. It's as if the battery was going flat

It cranks slowly for a few revolutions then spins normally and the car always starts after, maybe, a few seconds

Sometimes those first few cranks are so slow that you think the battery is just not going to turn it over then away it goes

We replaced the battery after about the first year but it made no difference

It failed to start for the first time a few days ago. It just cranked slowly and eventually cranked no more.

It eventually fired up "normally" about 20 minutes later after she let it sit a while. She wasn't very happy

It's done it's usual thing for the last few days

I have hooked the car up to my Star Diagnosis setup on a few occasions but no relevant faults are found

I am thinking that it might be the starter itself but it works perfectly after the first few slow cranks and if the engine is switched off and then started after a minute or so it works perfectly if you count one slow crank every time.

I've searched the various forums but there doesn't appear to be anyone out there who has experienced a similar problem

Does anyone have any clue as to what might be the cause of the problem?

Thanks

Peter

 

[Planethill]

What battery did you buy when you replaced it? What size and how many CCA?

It really can only be Battery, Battery/Starter Cables, Starter Relay (unlikely) or the Starter itself. Assuming the battery is the proper size, my money is on a tired/weak starter motor.

 

[Jim-ML320W164]

Check the cables from the battery to the starter motor for clean and tightness, all the way. The battery point under the bonnet may be corroded or/and loose too.

If you are really certain the battery is good (test it with an inductance tester or time how long it takes to run down from fully charged to dim with just a 55 Watt headlamp bulb connected across it, 20 hours is average for a 100 Amp-Hour battery) then the cables and starter motor are next suspects. Starter motors can do this, for a few months before they fail completely, I've had this on another car, long ago, and also listened to another Toyota Prado which my mechie was looking into which did that last month. The owner said that it had been doing it for about a year, sometimes slow cranking, sometimes as good as gold. But it didn't sound like my Prado, which always whirs into life. It sounded tired and softer.

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[Witek_M]

I am thinking that it might be the starter itself but it works perfectly after the first few slow cranks and if the engine is switched off and then started after a minute or so it works perfectly if you count one slow crank every time.

While cranking. Measure voltage drop between battery positive and large starter lug. Measure voltage drop between battery negative and engine. If less then 0.1 V replace starter. SR0827X

 

[Cowiepeters]

Thanks Planethill,

The battery was replaced with the same capacity as the original MB battery that was in it when we bought it. It was a good expensive brand, not a cheapie. The one I replaced was probably the second battery the car had had given that it was 8 years old at the time.
There was no discenible difference in the slow to crank issue.
The cables sound like the culprit. I'll have a look today
Thanks again,
Peter

 

[Cowiepeters]

Thanks Jim,

I'll have a look at them all today, the cables/joints certainly sound like the culprits
Peter

 

[Cowiepeters]

Thanks Witek,
I'll check the cables then have a look at the voltage drop.
It's got me puzzled why the first few revs to cranks are so slow and then it spins and starts so normally

Peter

 

[Cowiepeters]

I had a look under the car with a view to replacing the starter motor when I realised that it only cost USD$200.

The wiring all looked healthy but was mostly inaccessible to do a voltage drop test

A "Genuine" Bosch unit AUD$380 was delivered in 3 days from Pelican parts. They are easy to deal with and deliver to Australia

The access to stuff is awful and I needed to replace the steering box rubber mounts, CPS and engine mounts and had second thoughts

I gave it to my independent guy: Ross Firth at City Star Motors in Sydney on Tuesday and he had it all done by lunchtime Wednesday

Big thumbs up thanks Ross

All jobs were tricky with him resorting to cutting the steering box mount bolts and inserting new ones the other way around in order to avoid dropping the diff.

The bolts probably don't mind which way they are inserted

Anyway the car starts like a new one... spins for a second and starts immediately

Problem solved

I have dismantled the old starter motor but cannot identify any obvious faults. The brushes still have a decent amount of meat on them and the gear train and bearings all look good

Peter

 

[Jim-ML320W164]

Thanks for updating us Peter, much appreciated.

Glad your problem is sorted. I have no idea why the faulty starter motors do this, it's not the first time I've heard one and on different car marques too. It could be the commutators getting tarnished with age.

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[Planethill]

Yup. Sometimes they just get tired!