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W12 - Starting issues when hot

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Discussion starter · #21 ·
So......to get back to this.

Having used the car a bit it doesn't appear to be losing/burning coolant and there is no evidence of oil and water mixing. I've also had one of those chemical exhaust gas testers on the coolant tank and there is no evidence of a head gasket leak.

When I was at the local garage the other week collecting my V8 from getting some work done I was discussing this with one of the guys there and he mentioned a thing called "Starter Motor Heat Soak", he has a Boxster which has it; essentially, it seems that when a starter motor gets old the electrical winding becomes less efficient, heat from the engine increases electrical resistance and the SM basically stops working. This perfectly explains as to why it starts cold but sometimes not hot.

Starter Motor Heat Soak

I'll look into this some more and report back.

In the meantime, I've discovered it has a petrol leak somewhere around the tank/filler neck, the under-bonnet cooling fans has decided not to work (suspiciously immediately after it came back from it's insurance repairs) and the faulty suspension sensor still needs sorting!
 
#23 · (Edited)
AJL44 said:
So......to get back to this.

Having used the car a bit it doesn't appear to be losing/burning coolant and there is no evidence of oil and water mixing. I've also had one of those chemical exhaust gas testers on the coolant tank and there is no evidence of a head gasket leak.

When I was at the local garage the other week collecting my V8 from getting some work done I was discussing this with one of the guys there and he mentioned a thing called "Starter Motor Heat Soak", he has a Boxster which has it; essentially, it seems that when a starter motor gets old the electrical winding becomes less efficient, heat from the engine increases electrical resistance and the SM basically stops working. This perfectly explains as to why it starts cold but sometimes not hot.

Starter Motor Heat Soak

I'll look into this some more and report back.

In the meantime, I've discovered it has a petrol leak somewhere around the tank/filler neck, the under-bonnet cooling fans has decided not to work (suspiciously immediately after it came back from it's insurance repairs) and the faulty suspension sensor still needs sorting!
Click to expand...
I don't believe it, sounds more like a "scam" to replace expensive parts at your account because they simply don't know what is wrong. I wouldn't buy it...pointing the finger to another brand and model of car (Porsche) with a "similar" problem is BS.

The W12 has the autostart, it works or it doesn't. If the engine turns over but doesn't start the problem is not with your starter motor.
Have a look at the cooling temp sensor, especially the one at the back of the engine.
They do fail, the starter motors don't.
Had my cooling temp sensor replaced and didn't have any hard hot start problems ever since. If it's faulty it will give you all sorts of problems, overheating, poor fuel economy, hard start when hot, code's, CEL etc....

You also may want to look at the fuel you're putting in your car, avoid the E10. I know I do.
 
#24 ·
Olav-Black-W12 said:
I don't believe it, sounds more like a "scam" to replace expensive parts at your account because they simply don't know what is wrong. I wouldn't buy it...pointing the finger to another brand and model of car (Porsche) with a "similar" problem is BS.

The W12 has the autostart, it works or it doesn't. If the engine turns over but doesn't start the problem is not with your starter motor.
Have a look at the cooling temp sensor, especially the one at the back of the engine.
They do fail, the starter motors don't.
Had my cooling temp sensor replaced and didn't have any hard hot start problems ever since. If it's faulty it will give you all sorts of problems, overheating, poor fuel economy, hard start when hot, code's, CEL etc....

You also may want to look at the fuel you're putting in your car, avoid the E10. I know I do.
Click to expand...
Read the 1st post.
Car struggles to turn over when hot.
I had exactly the same symptoms and it was the starter.
 
Discussion starter · #25 ·
Future Shock said:
Read the 1st post.
Car struggles to turn over when hot.
I had exactly the same symptoms and it was the starter.
Click to expand...
This is correct. Thanks for the support. The engine isn't turning over (maybe barely) or even attempting to on the occasions when it doesn't start. There are also loads of threads on VW Vortex and other places about this phenomenon. Porsche, of course, is part of the VW group and has parts commonality with lots of VW's.

This is advice from a very reputable BOSCH service garage literally five or six minutes walk from my house (I've mentioned them previously) who have looked after the Phaetons since I've had them so they have no interest in hacking me off. They are inundated with work so don't need to cram in every available "mug" they think they can financially abuse.
 
#26 ·
Porsche, of course, is part of the VW group and has parts commonality with lots of VW's.
Click to expand...
Porsche has NOTHING to do with the design, engineering, build, parts of the Phaeton. Phaeton work started in the 90’s.

Porsche has never built a car of this caliber.

Modern Porsche have gotten better because of VW.


Sent from my iPhone using Tapatalk
 
#28 · (Edited)
AJL44 said:
This is correct. Thanks for the support. The engine isn't turning over (maybe barely) or even attempting to on the occasions when it doesn't start. There are also loads of threads on VW Vortex and other places about this phenomenon. Porsche, of course, is part of the VW group and has parts commonality with lots of VW's.

This is advice from a very reputable BOSCH service garage literally five or six minutes walk from my house (I've mentioned them previously) who have looked after the Phaetons since I've had them so they have no interest in hacking me off. They are inundated with work so don't need to cram in every available "mug" they think they can financially abuse.
Click to expand...
You have absolutely no clue about the Phaeton man and that's what you pay for.
Show a bit more interest in the car and the mechanics (and background) and it could save you a lot of money.
But whatever...
Certainly don't want to belittle on your "Bosch" experience because they are so trustworthy😁
In the Netherlands they are considered far from it, frauds...
 
#29 ·
AJL44 said:
This is correct. Thanks for the support. The engine isn't turning over (maybe barely) or even attempting to on the occasions when it doesn't start. There are also loads of threads on VW Vortex and other places about this phenomenon. Porsche, of course, is part of the VW group and has parts commonality with lots of VW's.

This is advice from a very reputable BOSCH service garage literally five or six minutes walk from my house (I've mentioned them previously) who have looked after the Phaetons since I've had them so they have no interest in hacking me off. They are inundated with work so don't need to cram in every available "mug" they think they can financially abuse.
Click to expand...
Replace the starter motor and feed back the change?
I fitted a LUCAS exchange unit. Cost £125 trade. Fitting on a W12 I can only imagine to be a right cluster fork. My diesel was awkward at best. Took about an hour though.
 
#30 ·
Future Shock said:
Replace the starter motor and feed back the change?
I fitted a LUCAS exchange unit. Cost £125 trade. Fitting on a W12 I can only imagine to be a right cluster fork. My diesel was awkward at best. Took about an hour though.
Click to expand...
It's an engine out procedure on the W12 (unless somebody here changed the starter with their W12 in situ).
 
Discussion starter · #33 ·
So, an update on this. The problem with the not starting when hot has changed a bit; whereas previously there was simply nothing at all when it tried to start it is now trying to turn the starter but unsuccessfully as though it had a flat battery. It did this yesterday but then started when I held the key in the start position rather than releasing it and letting the auto-start system start it. When it did, however, it ran really rough for the first few seconds like it was misfiring or something and then was fine.
 
#34 ·
AJL44 said:
So, an update on this. The problem with the not starting when hot has changed a bit; whereas previously there was simply nothing at all when it tried to start it is now trying to turn the starter but unsuccessfully as though it had a flat battery. It did this yesterday but then started when I held the key in the start position rather than releasing it and letting the auto-start system start it. When it did, however, it ran really rough for the first few seconds like it was misfiring or something and then was fine.
Click to expand...
Have you scanned it? Mine was throwing a problem on terminal 50, which I suspect is the trigger for the door lights to indicate an issue.

One other thing it might be is the crank speed reference sensor. When that starts to fail, it won't start when hot, but starts fine when cold, and it takes progressively less engine heat for it to start failing.
 
Discussion starter · #35 ·
invisiblewave said:
Have you scanned it? Mine was throwing a problem on terminal 50, which I suspect is the trigger for the door lights to indicate an issue.

One other thing it might be is the crank speed reference sensor. When that starts to fail, it won't start when hot, but starts fine when cold, and it takes progressively less engine heat for it to start failing.
Click to expand...
It's going in to get looked at tomorrow - for other things as well - so I'll ask them to look into it. Would any of the things you refer to cause the few seconds of rough running immediately on startup?
 
#36 ·
AJL44 said:
It's going in to get looked at tomorrow - for other things as well - so I'll ask them to look into it. Would any of the things you refer to cause the few seconds of rough running immediately on startup?
Click to expand...
No. If it's running rough, you'll probably have a code. The two W12s I've looked at in detail with rough running both had leaks from the intake manifold seals around the spark plugs.
 
#37 ·
invisiblewave said:
No. If it's running rough, you'll probably have a code. The two W12s I've looked at in detail with rough running both had leaks from the intake manifold seals around the spark plugs.
Click to expand...
Interesting. I just started having a lean condition on one of my W12. Do you remember were exactly the leak was? There are no intake seals at the spark plugs. Could it be the intake gasket it the center or one of the one on the outer halfs of the intake manifold?
 
#38 ·
Phaetonlvr said:
Interesting. I just started having a lean condition on one of my W12. Do you remember were exactly the leak was? There are no intake seals at the spark plugs. Could it be the intake gasket it the center or one of the one on the outer halfs of the intake manifold?
Click to expand...
On both of them there was a pool of oil around a couple of the plugs. I didn't see the manifold being refitted, I'd assumed there was a seal. It was easy to spot without taking the manifold off.
 
#39 ·
invisiblewave said:
On both of them there was a pool of oil around a couple of the plugs. I didn't see the manifold being refitted, I'd assumed there was a seal. It was easy to spot without taking the manifold off.
Click to expand...
The oil leaks at the spark plug wells is a common issue caused by brittle valve cover gaskets, however that's not part of the intake manifold and shouldn't have an impact on the air/fuel ratio. To get to the spark plugs on the W12 you either have to remove the complete intake manifold or just the outer parts on both sides.
 
#40 ·
Correct- no different than the 2.8 and 3.2 24v VR6- the spark plug holes just start to fill with oil- and eventually will misfire- eventually being the key word- long time.

It absolutely will NOT effect air fuel- physically impossible- but misfire can certainly cause rough running and will throw a code.
 
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