Sluggish starter when hot - S212 E500 (M273)

[ChrisPDuck]

I'd expect a failing starter motor to be at its worst turning over a cold engine - unless the heat is affecting the motor.

I'd have assumed so too, due to more viscous oil, but I could also believe an argument that a hotter engine might be harder to turn - expansion of the piston rings making for a tighter fit, residual compression in some cylinders which would have drained away overnight when things cool and loosen?

 

[Bellow]

I'd have assumed so too, due to more viscous oil, but I could also believe an argument that a hotter engine might be harder to turn - expansion of the piston rings making for a tighter fit, residual compression in some cylinders which would have drained away overnight when things cool and loosen?

The effect of the cold oil is significant and there's tighter clearances when cold also. Rings can't expand as such as because of being 'open'. It's always cold starting that catches out a weak battery.
That said, there are some engines that are notoriously difficult to start hot - BDA for one. Then again my SBC when hot will fire up with the merest rotation of the key. It ain't tuned on 45DCOEs to turn 10,000 rpm though.

 

[ChrisPDuck]

I checked the battery terminals - everything seemed clean and secure. For good measure I loosened them both and gave them a wiggle, then tightened them again, but I don't think they were the source of the problem.

I guess it's possible that there's a poor connection at the starter, but that's more difficult to check.

 

[MrGreedy]

Check that £500 for a new starter price.
You might be able to get refurbished from Merc and on either new or refurbished, there might be a return bonus. Specifically quiz MB Newcastle, and a couple of local MB dealers so return/exchange is easy. I think on my old Merc V6 starter wasn't as expensive, maybe something like £300 with £150 deposit return, so £150 actual cost, but that was circa 8 years ago.

 

[ChrisPDuck]

I’ve just heard from my friend in the trade. He’s found me a cracking price on a Bosch exchange unit (apparently Bosch ONLY do exchange units now). Presumably that makes it a factory refurb, which will be as good as new, and at the price he’s offering me there’s no point in me faffing around and getting mine refurbed.

I need to look harder for specific instructions for this model, in case I feel like tackling it myself, but I think I’m likely to take my replacement starter to my local garage.

 

[Bellow]

I guess it's possible that there's a poor connection at the starter, but that's more difficult to check.

That terminal is more likely a flat spade with a hole over a stud - which is less likely to expand/contract with temp variations.

I need to look harder for specific instructions for this model, in case I feel like tackling it myself, but I think I’m likely to take my replacement starter to my local garage.

Starter motors are pretty easy - with one exception I'll come to later.
Disconnecting the battery is the first step and under no circumstance can this be neglected. I cannot stress that enough. Remove electrical connections at the motor - the heavy supply cable and the lighter signal wire to the solenoid. Remove the two bolts retaining the motor then reverse the above to fit the new one.
Important is that the bolts are torqued to correct spec. The exception that prevents the job being as easy as outlined is access. Principally, there must be sufficient space to wield the tools to first remove the bolts then crucially to re-torque them. This may or may not involve the removal of other components and, if so, an assessment of your competence to deal with them (eg if breaking into fluid lines).
In summary, assess the task as per available access. If there is sufficient for the step by step tasks above then everything else is secondary and achievable. Access - or lack of - is the enemy. It always is!

 

[ChrisPDuck]

Thanks - yeah, it's the specifics of what else needs to be removed to access the starter that were my concern. They can make the difference between an easy job and one you wish you'd never started.

In fact I've now checked with my local garage, and their system is telling them it's an hour's job, which leads me to suspect that very little else needs to come off. But on the other hand, since they're only going to charge me for an hour I've decided to leave it to them! I'll save my enthusiasm for jobs that are easier for me to do on my drive

Paying more attention when I started the car cold this morning, it's definitely not what I'd call a lively starter, so I'm going to get it done now before it lets me down.

 

[Bellow]

Thanks - yeah, it's the specifics of what else needs to be removed to access the starter that were my concern. They can make the difference between an easy job and one you wish you'd never started.

Tell me about it!

In fact I've now checked with my local garage, and their system is telling them it's an hour's job, which leads me to suspect that very little else needs to come off. But on the other hand, since they're only going to charge me for an hour I've decided to leave it to them! I'll save my enthusiasm for jobs that are easier for me to do on my drive

The other item that crossed my mind that might end up being disturbed is the exhaust - and then there's a whole bunch of other possible stuff. A garage will be in a position to deal with anything.

Paying more attention when I started the car cold this morning, it's definitely not what I'd call a lively starter, so I'm going to get it done now before it lets me down.

'Lazy starter' is the term I think. First lazy - then dead.

 

[ChrisPDuck]

The other item that crossed my mind that might end up being disturbed is the exhaust - and then there's a whole bunch of other possible stuff. A garage will be in a position to deal with anything.

Yes, the exhaust is what I was most concerned about. Rusty/seized/snapped bolts are all much easier to deal with up on a lift. But I reckon if it's only an hour's labour, then access must be good - perhaps just an undertray or two to remove. I'll report back once they've done the job.

 

[MrGreedy]

That 'hour' to simply remove undertrays and decouple the exhaust near the flexi-connector/bend upwards could easily at home turn into 4 hours to butcher the exhaust off, plus then trying to sort a 'fix'. All on something that weighs an unbelievable amount once unhooked from the rubber hangers.

Whereas a grange will be able to get angle grinders/drills/cutters/impact drivers in there much more easily, and have the tools (welder, taps), parts and staff to get in back together as part of their day job. Unless the starter can be easily tackled from the top (e.g. Vauxhall 2.0 CDTI) then I'd rather pay for an hour. Wise choice Crispy