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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old January 14th, 2008, 14:14   #46
WriConsult
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0.3gph can't be right -- that's more than a lot of gasoline engines burn at idle. Much discussion of this at cleanmpg.com. Scurvy's figure of 0.16gph sounds more likely.

If you don't want to bother turning off and restarting your engine, fine. I can understand not wanting to go to the trouble for an extra couple mpg, but that's no reason to demean those who do. At a minimum, please spare us the rationalization of this as a safety issue. In half a million miles and 25 years of driving, I have seen exactly ONE situation where accelerating quickly from a stop actually prevented an accident, and that was a situation where the target vehicle was parked and wouldn't ordinarily have been running anyway.

BleachedBora's inference of about a quarter ounce a minute is about right. Doesn't sound like much, but those quarter ounces add up -- if you drive in congested areas a lot, you spend a LOT of minutes idling at lights over the course of a tank. An extreme but very real example for me: at rush hour, a 3-4 mile trip across Beaverton can easily take me 20 minutes, including 7-8 minutes idling at stoplights. In my Subaru I'll get 25-28mpg (seasonally varying) on this trip IF I kill the engine at lights, meaning I'll burn somewhere around 0.12 gallons to make the trip. If I leave my engine idling (0.25 gph) at the lights, that's another 0.03 gallons burned, increasing my fuel consumption by 25% for that trip.

Now granted, a diesel idles more efficiently than a gas engine. But remember that a TDI burns about half the fuel of my Subaru across the board, so proportionate savings is similar.

If you don't spend a lot of time sitting at lights, then you don't need to worry about this. And at shorter lights it's probably not worth the trouble for most people. But if you frequently find yourself stopped at long lights, killing your engine when you aren't using it is very much worth considering. The savings are substantial.

Last edited by WriConsult; January 14th, 2008 at 14:36.
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Old January 14th, 2008, 15:41   #47
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No one has addressed starter wear....I bet they LOVE be utilized at 10x the normal rate! Maybe they enjoy being energized 11ty billion times a day?
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Old January 14th, 2008, 17:07   #48
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Quote:
Originally Posted by dee_zell
Quote:
Originally Posted by rotarykid
Last clutch in my 85 TD lasted 700,000 miles ...
Had one last 900,000 mies on a 79 Celica ...
Got almost 600,000 miles on an 82 Celica the same... .
Got over 500,000 on a 80 Rabbit 1.5 LS without a clutch .



Holy Cheeses! You must've been to the Moon quite a few times my friend!
I stand by these numbers . Try going form NC to Seatle & back and NC to Denver & back regularly over the last 25+ years . Or the 200 miles a day drives when I was younger . Also I wasn't always the only one driving these cars . All those miles do add up .
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Old January 14th, 2008, 17:12   #49
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Originally Posted by rotarykid
I stand by these numbers . Try going form NC to Seatle & back and NC to Denver & back regularly over the last 25+ years . Or the 200 miles a day drives when I was younger . Also I was always the only one driving these cars . All those miles do add up .
You would imply that you lose economy charging pm the battery to replace the lost energy from cranking with the starter? Thats worse then saying that DRLs hurt economy.

My ass......
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Old January 14th, 2008, 17:23   #50
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Originally Posted by validius
You would imply that you loose economy charging pm the battery to replace the lost energy from cranking with the starter? Thats worse then saying that DRLs hurt economy.

My ass......
How many amps do you think you use to run the starter & glow plugs when the engine is cold ?? I'm betting if you make that statement you haven't driven auto diesels for very long . Glow plugs heating up are like having a dead short on the battery and much strain is put on the engine burning fuel replacing those used amps .

Have you ever heard an alternator belt squeal after a cold start ?? , I'm betting you have just as I have . Just Take a drive in an old 1.6 L A2 diesel when cold after a cold start and then tell me there is no extra strain on the engine after a cold start .

DTRL running lights also pull juice but @ 80 % of full light load .
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Old January 14th, 2008, 18:09   #51
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Quote:
Originally Posted by validius
You would imply that you loose economy charging pm the battery to replace the lost energy from cranking with the starter?
What we have here is a failure to read my signature.
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Old January 14th, 2008, 18:12   #52
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Originally Posted by darkscout
What we have here is a failure to read my signature.
And what you have is a failure to remove your head from your ass
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Old January 14th, 2008, 18:16   #53
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Quote:
Originally Posted by rotarykid
How many amps do you think you use to run the starter & glow plugs when the engine is cold ?? I'm betting if you make that statement you haven't driven auto diesels for very long . Glow plugs heating up are like having a dead short on the battery and much strain is put on the engine burning fuel replacing those used amps .

Have you ever heard an alternator belt squeal after a cold start ?? , I'm betting you have just as I have . Just Take a drive in an old 1.6 L A2 diesel when cold after a cold start and then tell me there is no extra strain on the engine after a cold start .

DTRL running lights also pull juice but @ 80 % of full light load .
Lets just assume your right. Its a large assumption but il leave it to VeeDubTDI and darkscout to argue if they so desire.

You honestly expect me to believe that the MINOR increase in econoemy is worth the rough duty cycle being put on the driveline by pop starting all the time? The halfshafts being banged around like that and the clutch being improperly used.
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Old January 14th, 2008, 18:24   #54
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Quote:
Originally Posted by validius
And what you have is a failure to remove your head from your ass
Dude, don't loose your mind. I was just making a joke up they're. If you come off you're rocker that quickly I wonder what you have up their in your noggin. Sounds like a screw lose or something. I mean I didn't try to effect you in anyway, but now look how you've gone and disrupted the affect the original poster had. Here me out, there are a lot of people that are knew hear. You should calm down than come back.
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Old January 14th, 2008, 18:43   #55
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Quote:
Originally Posted by darkscout
Dude, don't loose your mind. I was just making a joke up they're. If you come off your rocker that quickly I wonder what you have up their in your noggin. Sounds like a screw lose or something. I mean I didn't try to effect you in anyway, but now look how you've gone and disrupted the affect the original poster had. Here me out, there are a lot of people that are knew hear. You should calm down than come back.
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Old January 14th, 2008, 19:30   #56
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Keep it clean guys--we're trying to help everyone here .
As always, YMMV.
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Old January 14th, 2008, 19:37   #57
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Quote:
Originally Posted by scurvy
This sounded very odd to me, so I pulled out my HEX-USB+CAN cable and fired up Vag-Com Beta 711.1 to check on my 2006 Golf. I neglected to get logs, so I'll do that this evening.

Let's work in native units, which Vag-Com (and the ECU) work in. You verified 0.3 gallons/hour at warm idle. 1 US gallon = 3.785 liters (source) & 1 liter = 0.264 US gallons (source), so you say that at warm idle, you're burning (0.3 US gal * 1 liter/0.264 US gal) 1.136 liters per hour.

I fired up Vag-com when I went to lunch, and with all accessories off and the engine idling from a cold start, Vag-com was reporting fuel consumption of 0.6 liters/hour (53% less than your figure).
Once it was fully warmed up (after a half hour drive), Vag-com reported 0.4 liters/hour (65% less than your figure) at idle with all accessories off.

Unless you had every single accessory blazing while you took these measurements (plus a few extras) or mistook the Vag-com measurements for gallons/hour when they are actually liters/hour (which IMO is probably the crux of the issue), I don't see how this is possible unless your car has injector issues. Many other users have reported nearly the same figures (0.3 - 0.4 liters/hour at warm, accessories off idle) from Vag-com, which gets its information from the engine ECU.
Thanks for the info. This is a bit of a mystery becaue my vag-com (version 409.1) shows .8-1.0 liters per hour in group 15, zone 3. That exactly agrees with SC (they are possibly both reading the same value). My SC reports very accurate fuel usage now that it's calibrated (my correction is -30%) but certainly could be accurate while driving and way way off at idle.

Obvioulsy I didn't have every (any, actually) accessory running - not even DRLs.

I'm starting to wonder if I don't have something wrong somewhere. But something wrong that only affects idle? My driving MPGs are in the mid 40s...about right for an auto PD. Any thoughs?

Gene
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Old January 14th, 2008, 19:48   #58
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Quote:
Originally Posted by scurvy
This sounded very odd to me, so I pulled out my HEX-USB+CAN cable and fired up Vag-Com Beta 711.1 to check on my 2006 Golf. I neglected to get logs, so I'll do that this evening.

...
Scurvy? You have an auto or manual? Could this account for the large difference? I know shifting from "D" to "N" while stationary reduces the fueld consumption by about 30% (the .3 gal/hour I see is in "N", in "D" it hovers closer to .4). It might...that torque converter's still spinning in "N" right?

Anyone with an Auto PD and SC or VAG have any numbers to chime in with?
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Old January 14th, 2008, 20:27   #59
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MANual, of course. Any PD or VE engine idling in neutral and fully warm should give 0.3 - 0.4 liters per hour.

Quote:
Originally Posted by DFWDieselJet
This is a bit of a mystery becaue my vag-com (version 409.1)
I can't help but think this might be an issue. Are you using a cheapo ebay cable? How about getting somebody else to hook up a recent version of Vag-com to your car and seeing what it says.

I logged data, but won't get the chance to tidy it up until tomorrow.
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Old January 15th, 2008, 14:11   #60
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Quote:
Originally Posted by Bob_Fout
No one has addressed starter wear....I bet they LOVE be utilized at 10x the normal rate! Maybe they enjoy being energized 11ty billion times a day?
No one has addressed it here, but it certainly has been addressed elsewhere. Starter failure is mostly caused by a combination of age and the heat generated by long crank cycles. The short crank cycles of starting up an already warm engine don't make as much difference as you might think.

http://www.cleanmpg.com/forums/showthread.php?t=6650

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