Stop-Start. A different query

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Mike Rometer
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Re: Stop-Start. A different query

Post by Mike Rometer » Tue May 07, 2019 2:22 pm

We're slightly at cross purposes here, I have the Ford petrol anyway. But unless the electric pump keeps running (probably does, which is great) then when bearing surfaces stop moving their weight will cause them to settle through the oil film and can allow metal to metal contact. On re-starting the oil is drawn round with the parts and that will lift them apart again, it's called the hydro-dynamic wedge. It's only that contact bit that is the worry. As regards all of this, I would hope/expect that ALL the manufacturers have got this point well sorted by now.
Last edited by Mike Rometer on Tue May 07, 2019 5:32 pm, edited 1 time in total.
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Late for Tea
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Re: Stop-Start. A different query

Post by Late for Tea » Tue May 07, 2019 5:24 pm

Say or think what you will, but start stop will definitely affect component life. This is a big part of the reason I chose to disconnect mine.


Wastegate84
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Re: Stop-Start. A different query

Post by Wastegate84 » Tue May 07, 2019 6:41 pm

Mike Rometer wrote:
Tue May 07, 2019 2:22 pm
We're slightly at cross purposes here, I have the Ford petrol anyway. But unless the electric pump keeps running (probably does, which is great) then when bearing surfaces stop moving their weight will cause them to settle through the oil film and can allow metal to metal contact. On re-starting the oil is drawn round with the parts and that will lift them apart again, it's called the hydro-dynamic wedge. It's only that contact bit that is the worry. As regards all of this, I would hope/expect that ALL the manufacturers have got this point well sorted by now.

What electric oil pump?????


BOBCDP
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Re: Stop-Start. A different query

Post by BOBCDP » Tue May 07, 2019 7:57 pm

Late for Tea wrote:
Tue May 07, 2019 5:24 pm
Say or think what you will, but start stop will definitely affect component life. This is a big part of the reason I chose to disconnect mine.
+1 Exactly what I think. It is bound to increase component wear and will nacker your battery well before it should be nackered. I always switch s/s off and my car is coming up to 4 years old. s/s works every time I forget to switch it off. I have no doubt at all why that is. 😊😊
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chrisjp
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Re: Stop-Start. A different query

Post by chrisjp » Tue May 07, 2019 8:08 pm

Vespa wrote:
Tue May 07, 2019 1:53 pm
A bit about oil circulation from the PDF
An electronically controlled variable flow oil pump with integral vacuum pump matches its flow rate according to engine speed,
load and temperature. Oil flow to the piston cooling oil jets is solenoid controlled and operates only when needed
The key point here is that the oil pump is electronically controlled - it is not electrically operated. In fact it is driven by chain from the crankshaft just like most other internal combustion engines, diesel or petrol. This means that, as usual, when the engine stops the oil pressure will drop to zero and will only build back up again once the engine is again rotating at at least idle speed. So I think the stop-start system will cause extra wear on the plain shell bearings that are on the crankshaft. These are not roller bearings (and could not be without somehow splitting the crankshaft into many pieces to allow roller bearing fitment). As other people have said, only time will tell whether the stop-start system will lead to premature bearing failure - and by premature I mean before well over 100,000 miles. Modern engines are, with proper oil and filter changes, now perfectly capable of going to 200,000 miles without overhaul. I ran a 2 litre petrol Vauxhall Cavalier to 230,000 miles without engine overhaul and it was still going strong when I sold it.
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Gojira
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Re: Stop-Start. A different query

Post by Gojira » Tue May 07, 2019 8:29 pm

Call me a wild-eyed optimist if you like, but I would expect Jaguars engineers have thought about all the problems we can come up with for wear caused by stop/start and done something about them! :)

Then again, I'd also expect it to have worked reliably for everyone from day One, so I -might- possibly be wrong :oops:
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ChrisGB
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Re: Stop-Start. A different query

Post by ChrisGB » Tue May 07, 2019 8:45 pm

It's all a bit new technology wise, but my personal experience of stop / start has been ok. Cars I've had with it on and the mileages they where sold on at in good working order:

Bini (BMW Mini) Cooper D 154,000
Kia Rio CRDi 104,000
Skoda Citigo Green tech 104,000
Skoda Citigo Green tech 89,000

Bear in mind that all of these where used almost exclusively as training cars, so they get stalled and laboured too. I think that's a pretty good track record.

Modern ester synthetic oils can really help in the start cycle. Although the hydrodynamic wedge collapses when the engine stops turning, the boundary film strength of these ester oils is phenomenal and I'm sure this helps protect the bottom end until the wedge is re-established.

Interestingly, my latest training car has a motor generator unit that acts to restart the engine and augment torque too. It's belt connected and much more sophisticated in operation than the XE system!
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Vespa
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Re: Stop-Start. A different query

Post by Vespa » Wed May 08, 2019 8:33 am

I never said that the main and small end bearings were roller bearings. I said there are more roller bearings used in this engine.Where the idea of roller bearings on big ends and small ends came from is beyond me. :x
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wdig
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Re: Stop-Start. A different query

Post by wdig » Wed May 08, 2019 8:45 am

Roller big end bearings - Motorcycles esp old British.


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PhilB
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Re: Stop-Start. A different query

Post by PhilB » Wed May 08, 2019 8:55 am

Am I being a bit naive here?
I don't think stopping the engine for a few seconds will see all the oil disappearing into the sump and leaving components dry and unprotected.
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