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Old 03-29-2012, 05:39 AM   #11 (permalink)
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Turbos on diesels don't glow red anymore. 15 years ago when NOx output was barely regulated, they did. 1200F EGT, no problem. Modern de-NOxed diesels with high EGR flow (30-50% of the intake charge) can barely make 800F EGT.

That being said, I wouldn't recommend shutting it down at red lights. Modern diesels need to keep heat in their aftertreatment systems. It's not like a gas engine that will merely pollute more if the cat cools down too much. A diesel will get constipated pretty quick if proper aftertreatment temps are not maintained.

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Old 03-29-2012, 10:43 AM   #12 (permalink)
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Yea I'm not gonna risk it.
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Old 03-29-2012, 11:47 AM   #13 (permalink)
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The new common-rail VWs will run more regen cycles to keep the DPF burned out, and end up wasting more fuel.

Keep it running.
I'm not coasting, I'm shifting slowly.
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Old 03-29-2012, 12:03 PM   #14 (permalink)
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But when the engine is idling the exhaust gas' temperature is too low to burn out soot/PM, so it does not help the DPF. On the other hand, it may produce more PMs for the DPF to catch.

Low load (idle) -> low EGT -> more PM, less NOx
High load -> high EGT -> less PM, more NOx
e·co·mod·ding: the art of turning vehicles into what they should be

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Piwoslaw's Peugeot 307sw modding thread

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Old 03-29-2012, 07:17 PM   #15 (permalink)
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Just about all European low CO2-emission (<100 g/km) cars now have stop-start systems.
Just about all of them are diesels.
They have improved starter-engines, though diesels already had beefier starter engines.

Don't kill it when it's still cold though.
Once it's warm, forget about yer old sayings, old habits.
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Old 03-30-2012, 04:56 AM   #16 (permalink)
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Originally Posted by Piwoslaw View Post
If you are hypermiling, then your turbo probably didn't get too hot to begin with.

If you're constantly flooring it trying to gut the engine, then your turbo will be glowing red, but then you probably don't care about saving fuel anyhow.
Like I said... if you're driving gently, it's probably not such a big deal... but VGTs are very sensitive... much more so than regular turbos. If there's an auxiliary pump that keeps the coolant and oil circulating even with the engine off, no problem. I've driven a lot of new turbocharged cars where there's a ridiculous amount of whine and thrum coming from under the hood even after the ignition is turned off, so I suppose they already do something like this for many cars with VGTs.
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Old 03-30-2012, 05:35 AM   #17 (permalink)
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I imagine you've probably made slow progress gettintg to the button you need to get out and press, so Turbo is probably cool enough. But as far a turbo cooling goes, whether it is coolant or oil cooled if it is hot, ie just had a real hard run and stopped, the engine does need to idle for a few minutes to cool the unit down and allow the turbine bearing to stay lubricated while turbine slows down.
A lot of new vehicles may well have shutdown protocols, but that does not necesarilly mean it is appropriate for all vehicles.
Is it really 1 minute to get out and press a button and get in and drive on?
My vote is less than 1 minute leave it running.
1-3m, whatever you think is appropriate.
More than 3min, shut it down.
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Old 03-30-2012, 06:39 AM   #18 (permalink)
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When city driving, I never hit the boost, engine temps are struggling to get up, luckily I don't need to drive in city that often, even rare is that I would meet traffic lights.

I turn off engine at traffic lights, but mostly when I know stop is tad longer, cool off is happening all the time at city driving, that is if you are driving sensible, as one is idling most of the time when hypermiling at city, so there is no difference for me when turning it off normally or at traffic lights.

It is not really fuel saving, but noise saving, why to keep making lot of noise when one can sit in silence?

Don't know about modern things, but I'm not too fond of them either, I can make old one to go as little or even less fuel because less of weight

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Old 03-30-2012, 12:54 PM   #19 (permalink)
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Originally Posted by Tesla View Post
My vote is less than 1 minute leave it running.
1-3m, whatever you think is appropriate.
More than 3min, shut it down.
That is about as close as one can get. A long traffic light, so what?, whereas waiting for a train would be different.

Some of these diesels are hard to turn over. And a pair of $200 batteries doesn't make that any easier with multiple stop/start. One could too easily find the limit on the wrong day in the wrong place as to how many re-starts without full re-charge on the batts. Or wear down a $400 starter too soon. Etc. It's a different budget for maintenance & repairs versus book guidelines.
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Old 03-30-2012, 06:59 PM   #20 (permalink)
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I always feel so sorry for the local diesel owners; evidently they have to go through hell and high water to get their engines started and so once running, they never shut them off.

What? All they have to do is turn a key? Who knew!


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