Fuel consumption when idling

Does anyone notice that when idling, they burn through fuel rather quickly? I basically live in my car for work, and I have a fair amount of down-time, so I will frequently pull into a shopping center parking lot and read a book or use the laptop. I notice that during a 1 hr period that I may sit idling, the average fuel consumption on my MFI will drop by sometimes 2 mpg. I know the MFI isnt the best measure, but it still does count for something. Is this normal? Has anyone noticed anything similar?

To be frank I'd be more concerned about running my car at idle for an hour than a 2mpg MFI read out difference..

I burn between 0.2-0.3 Gal/hr at idle on a warm engine, as compared to ~1.5 GPH at 70mph (according to VAG-Com and Scangauge II). Those numbers are based on Summer fuel blends though.

Scangauge reports 0.09 to 0.11 gph on an ALH. I wonder why the CR engines seem to use so much more....

UFO said:

Scangauge reports 0.09 to 0.11 gph on an ALH. I wonder why the CR engines seem to use so much more....

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My guess would be Post Combustion Injection to get the emission systems (DPF, Cats, etc.) up to and keep them at operating temps. According to the research I've done, active DPF regens aren't the only time PCI occurs.

Also, aren't the ALH engines 1.9L? (vs. 2.0L on the CR)

Yes, it's normal. When you're getting 0mpg when idling, it will indeed suck your mileage down.

And, the MFA on the '09+ cars is pretty darn accurate. I've been kept track of mileage on every tank of the 40k miles I owned my '09 and the ~6k I've owned my '10. The MFA is usually within +/- .5MPG of my hand calculated (pencil & paper) MPGs.

BTW, 'acrossthepond' makes a good point. I'd be cautious about extended idling as a routine. Occasionally is probably fine, especially if followed by highway driving to burn off any accumulated soot in the DPF.

There is a growing movement out there that is trying to spread the word: cars and trucks (yes, semis and heavy machinery too) don't like to idle. They like to work. Take a look at the next big truckstop you see. Many truckstops along the interstates are setting up "docking" facilities for trucks so that the drivers can utilize their onboard systems without the engine running.

While the engine itself has no issue running quietly along at minimum rev, all the other systems suffer. These systems, particularly the exhaust system, are designed for DRIVING conditions, not idling conditions. The first thing that's going to happen is that all of your emissions control devices/elements are going to deteriorate or become clogged. On the new CR diesels, the DPF will clog and need a regen, which it will hopefully be able to handle on its own (and thereby using more fuel). Other exhaust systems relying on catalyst filters (such as a catalytic converter) will have their lifespan shortened.

Additionally, the engine management system will adjust the engine settings as best it can to produce as few emissions as possible. This can result in sensors getting fouled and misreadings to occur.

If you want to stop for an hour or so and work, I'd recommend dropping in on a local cafe (which usually have better WiFi policies than Startbucks, and better snacks), or if you really enjoy working in the car, maybe consider integrating a deep cycle storage battery to run your laptop while you're parked. Running the engine isn't good for the car, will shorten the life of your exhaust components, wastes fuel and pollutes.

If you have the consumption set to read in "liters per 100k", the MFD shows how much fuel you are wasting at idle. Mine wastes 0.6L per hour idling.

tcp_ip_dude said:

I burn between 0.2-0.3 Gal/hr at idle on a warm engine, as compared to ~1.5 GPH at 70mph (according to VAG-Com and Scangauge II). Those numbers are based on Summer fuel blends though.

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VCDS (VAG-COM) reports fuel consumption in Liters/hour. I think you mean 0.2-0.3 L/hr at idle when warm.

n1das said:

VCDS (VAG-COM) reports fuel consumption in Liters/hour. I think you mean 0.2-0.3 L/hr at idle when warm.

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The '10 MFA can display L/hr if you set it to do so.

n1das said:

VCDS (VAG-COM) reports fuel consumption in Liters/hour. I think you mean 0.2-0.3 L/hr at idle when warm.

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Negative.. I'm seeing approximately 0.2 GPH, my primary readings are from the Scangauge since it's always hooked up and the SG reads in GPH. A friend was showing me the ropes on the VAG-com over the summer and were trying to verify some of the SG readings. Can't swear by the VAG-com readings as I'm still a rookie at that.

n1das said:

VCDS (VAG-COM) reports fuel consumption in Liters/hour. I think you mean 0.2-0.3 L/hr at idle when warm.

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0.3L/hr is crazy low. The 2.0 TDI is closer to 0.7L/hr at idle. Have a feeling the extremely lean operation at idle was bad for emissions, so they have to dump more fuel in now to keep things meeting spec.

seftonm said:

0.3L/hr is crazy low. The 2.0 TDI is closer to 0.7L/hr at idle. Have a feeling the extremely lean operation at idle was bad for emissions, so they have to dump more fuel in now to keep things meeting spec.

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During warmup on a CR-TDI there's a post-injection to help speed up the warming of the OxCat & DPF. If with a warm engine the DPF temp drops too low, the ECU will probably resume the post-injection, but I doubt there's any arbitrary fuel dumping. Most of the time more fuel = more emissions.

I'm seeing 0.6-0.7L/hr pretty much all the time when warm, never seen below 0.6. Cold, it's more like 1L/hr. More fuel is usually worse for emissions, but it seems NOx was one of the hardest targets to meet with this engine, and lean burning makes lots of NOx. Hence my suspicion that they're burning more fuel to keep NOx down.

seftonm said:

0.3L/hr is crazy low. The 2.0 TDI is closer to 0.7L/hr at idle. Have a feeling the extremely lean operation at idle was bad for emissions, so they have to dump more fuel in now to keep things meeting spec.

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tcp_ip_dude said:

Negative.. I'm seeing approximately 0.2 GPH, my primary readings are from the Scangauge since it's always hooked up and the SG reads in GPH. A friend was showing me the ropes on the VAG-com over the summer and were trying to verify some of the SG readings. Can't swear by the VAG-com readings as I'm still a rookie at that.

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0.3 L/hr is the norm for older TDIs (1.9L and no DPF). That's probably what threw me for the CR (2.0L and DPF-equipped) TDIs which are around 0.7 L/hr (~ 0.2 GPH).

Here's what I've found after waiting for friends in my car for about an hour and playing with my computer:

0.7L (.18gal) /hr = Engine temp nominal (90C), Headlights off, E-Brake up (no DRL), AC off.
0.8L (.21gal)/hr = Engine temp nominal (90C), Headlights on, AC off.
0.9L (.24gal)/hr = Engine temp nominal (90C), Headlights on, AC on.
0.9L (.24gal)/hr = Engine temp 3/4 nominal, Headlights on, AC off.
1.0L (.26gal)/hr = Engine temp 3/4 nominal, Headlights on, AC on.
1.1L (.29gal)/hr = Engine cold from overnight (outside temp -5C/23F), Headlights on, AC off
1.2L (.32gal)/hr = Engine cold from overnight (outside temp -20C/-4F), Headlights on, AC off

Is there a way to lower your idle RPM? I'd love to hit a ridiculously low idling consumption like 0.3L (.09gal)/hr or something.

Is there a "high idle" switch for the TDIs?

The big rigs and even some pick-up truck diesels have a High Idle switch or setting when in Park that the idle speed is increased to run more efficiently.

From what I understand the low piston speeds increase side load on the piston skirt and extended idling will lead to odd and destructive bore wear.

Pillow said:

Is there a "high idle" switch for the TDIs?

The big rigs and even some pick-up truck diesels have a High Idle switch or setting when in Park that the idle speed is increased to run more efficiently.

From what I understand the low piston speeds increase side load on the piston skirt and extended idling will lead to odd and destructive bore wear.

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No.

TDIs have been in North America for 15 years and there's still no high-idle device available.

I've noticed my 2011 golf TDi uses .7-.8 idling in drive, .6 in neutral after warmed up at 20*C. My old 2001 Jetta TDi only used .3P per hour. Here emissions aren't regulated so I'm probably going to be doing the Rawtek EGR and DPF delete and do a stage 2 Malone tune. hopefully looking at reducing my idle to .3L per hour.

Malone 2 / Rawtek has not changed the idle fuel consumption on my car. Still 0.7 to 0.8 litres/hr according to MFD once warmed up. Only see it at occasional traffic lights so not of any concern

Wow sport tune for idling. That's a new one. How much idling are you doing? Hours at a time?

Ive seen anywhere from 0.7 to 1.3 l/100 km depending on temp and a/c.

Sorry to resurrect a dead thread but I did a 30 second search and found nothing newer...

Last I was skiing at Jay Peak in Vermont and it was -23C/-9F on Friday morning so there was a good chance my car wouldn't start in the morning so I let it idle overnight. It burnt about an 1/8th of a tank. Assuming a 55L tank that works out to be about 0.625L/hr. Not entirely scientific but it gives you a ballpark estimate of how much a TDI (ALH) will burn at idle.

And yes, the car was up to full operating temp in the morning. Oh and it's a good idea to keep your locks lubed up in case the keyfob doesn't want to work all of a sudden. I had a little scare.

I have many hundreds of hours idling on my ALH, it burns right at .25 gal/hr because doing a fill right to the lip and then idling for 8 consecutive hours with the AC on, filling up after that it took 2 gallons.

I haven't done the same test with my new CR TDI yet, but the Scangauge shows similar fuel usage while idling.

Nice to see some data! Thanks for those who have shared their findings. I left the car idling the other day while what was supposed to be a quick visit..... 1.5 hrs later... but it was -28 out so a warm car is worth a few litres of fuel, even at our stupid Canadian prices! (1.20liter) one downfall to a 6sp, too hard for a remote start.

Once, by accident, I left my car idling for 16 hours overnight in my driveway. I left it it running to finish a regen and forgot all about the car. The link below is the thread.

ksing44 idling for 16 hours

When I refilled the tank, I figured ~ 0.17 gallons per hour (gph) after 16 hours of idling.

ksing44 said:

Once, by accident, I left my car idling for 16 hours overnight in my driveway. I left it it running to finish a regen and forgot all about the car. The link below is the thread.
ksing44 idling for 16 hours
When I refilled the tank, I figured ~ 0.17 gallons per hour (gph) after 16 hours of idling.

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According to my scangauge, that seems to be about right for the CR diesels. I haven't verified it yet.

I should also mention actual data on the ALH without the AC running (cold outside temps, running the heat only) seems to use about .17 gal/hr as well. So the AC compressor adds about .08 gal/hr.