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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Mon, Jul-31-2017, 09:48:01 PM   #31
Drewster
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Default Re: Getting Gas with the Engine Running

Personally, I wonder about the possibility to damage the EVAP system. I know in some cars, you can end up filling the charcoal canister with fuel by constantly over-filling - I'd imagine that having the purge pump/ solenoids going while there's a bunch of sloshing fuel probably isn't the best thing..
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Old Mon, Jul-31-2017, 10:10:18 PM   #32
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Default Re: Getting Gas with the Engine Running

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Originally Posted by Obioban View Post
Different parts expand as they warm up at different rates. The parts are designed to be correctly sized, and fluids are speced to be at the correct viscosity, when at operating temperature. Warming up at idle makes it take longer to warm up. The longer it's running cold, the more wear is occurring.

The owners manual for the car even specifies that you should not let it warm up at idle.
Furthermore, only the engine warms up at all at idle. The trans and diff are basically as cold as they are when off if the car is just idling.
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Old Mon, Jul-31-2017, 11:20:59 PM   #33
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Default Re: Getting Gas with the Engine Running

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Originally Posted by TheSt|G View Post
Furthermore, only the engine warms up at all at idle. The trans and diff are basically as cold as they are when off if the car is just idling.
Ahhhh, good point, good point.
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Old Tue, Aug-01-2017, 12:50:11 AM   #34
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Default Re: Getting Gas with the Engine Running

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Any thoughts on idling for 1-2 mins before shut off after hard driving?
Another good topic. Driving at 80 mph, pull off for a gas station and stop at pump all in 30 seconds. Probably also a good idea to let it idle for a minute or two. Especially with the 135 twin turbo. If you have ever turned on the ignition just after stopping an engine you will see the temp go up quite a bit.
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Old Tue, Aug-01-2017, 01:25:49 AM   #35
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Default Re: Getting Gas with the Engine Running

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Another good topic. Driving at 80 mph, pull off for a gas station and stop at pump all in 30 seconds. Probably also a good idea to let it idle for a minute or two. Especially with the 135 twin turbo. If you have ever turned on the ignition just after stopping an engine you will see the temp go up quite a bit.
Reminds me of a war memoir I read once, of a German Tiger commander. They were trying to outrun the Soviets in the closing days of the war, racing westward to make it to American lines. This particular crew were the final surviving tank of their 5-Tiger 'schwadren' from a few days prior.

They had made it to a small pocket of German units that were grouping up to attempt a morning break-out (they'd become overrun and surrounded by Russians who may or may not have known they were there, I can't recall).

But as they rolled into this small pine forest, the driver noted that the oil pressure on their mighty Maybach HL... 260 I think - a gigantic V12 - had been near zero for the entire day. And hot gear oil had been spitting out at him from the transmission housing right next to him. Still, the beast pushed on.

They drove to beneath some thick overhead cover and had to make a decision: keep the engine running and keep coolant cycling, or shut it down and risk it ceasing up. They knew that the block temperature would rise substantially once they shut it down. They looked around for gasoline and couldn't find any, so they shut it down.

The author noted that the engine was so hot, it was sizzling and cracking and popping for half an hour as it cooled.

The next morning: vvvvvRRMMmmmmmm - it fired up again, and they made it over 100km before successfully surrendering to the Americans.
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Old Tue, Aug-01-2017, 02:54:27 AM   #36
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Default Re: Getting Gas with the Engine Running

Don't ever idle your car at a gas station, idiots.


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Old Tue, Aug-01-2017, 04:04:18 AM   #37
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Default Re: Getting Gas with the Engine Running

I still don't see why a brief idle warm up (< 2-3 mins) is bad for the engine.
Assuming it takes X revs to warm up the engine, then it may take more time, but no fewer cold revs than warming it up at speed. And I don't see why different rates of expansion would change this - if anything I'd think a prolonged, steady warm up would be better for parts that expand at different rates. But I am no mechanical engineer.
But further, why not rev it up nice and high right away, and get it warm extra quickly? We obviously wouldn't do that, so what's the sweet spot? We don't have oil pressure gauges, and what's optimal probably depends on ambient temperature.
I don't buy it just because BMW says it - for all we know, they're saying it so that your cats get up to temp quicker or to prevent inhalation of exhaust gasses. It's interesting that in some cases people think whatever BMW says is to be taken for pure truth, and in other cases we're happy to prove they're undeniably wrong (vanos, subframe, OCIs, whatever).
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Old Tue, Aug-01-2017, 11:20:04 AM   #38
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Default Re: Getting Gas with the Engine Running

Keep in mind [also] that the piston rings need a lot more cylinder pressure to expand and seal when cold. Idle doesn't produce enough pressure to accomplish this, until the engine is up to running temp.

What you're essentially doing by sitting at cold idle, and the extent is dependent on the condition of your motor, is washing the bores of oil (cold starts/warm-up = fuel enrichment) and allowing more blow-by to enter the crankcase, subsequently contaminating your oil.

Getting gas with the car running, eh, I kinda do that too sometimes
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Old Tue, Aug-01-2017, 11:51:22 AM   #39
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Default Re: Getting Gas with the Engine Running

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Originally Posted by WyattH View Post
I still don't see why a brief idle warm up (< 2-3 mins) is bad for the engine.
Assuming it takes X revs to warm up the engine, then it may take more time, but no fewer cold revs than warming it up at speed. And I don't see why different rates of expansion would change this - if anything I'd think a prolonged, steady warm up would be better for parts that expand at different rates. But I am no mechanical engineer.
But further, why not rev it up nice and high right away, and get it warm extra quickly? We obviously wouldn't do that, so what's the sweet spot? We don't have oil pressure gauges, and what's optimal probably depends on ambient temperature.
I don't buy it just because BMW says it - for all we know, they're saying it so that your cats get up to temp quicker or to prevent inhalation of exhaust gasses. It's interesting that in some cases people think whatever BMW says is to be taken for pure truth, and in other cases we're happy to prove they're undeniably wrong (vanos, subframe, OCIs, whatever).
You think BMW actually cares about cats/emissions outside of their standardized testing/ratings? BMW isn't the only engineering/car company that recommends driving to warm up an engine.

I believe the point is to minimize time running a cold engine. Sure, the engine warms up with friction which increases basically linearly with revs, but combustion also helps warm it up. At idle there's hardly any air/fuel mixture going through there; under load the engine is happier and warms up quicker still. So it doesn't just take 'x' revs to warm up. My theory is that the engine's cold oil pressure and relative tolerances may offer roughly the same protection whether the engine is at 1k or 3k rpm. Sure the engine is spinning faster which basically assumes greater wear, but it was designed more around 3k rpm partial throttle in gear rather than just idle.

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Old Tue, Aug-01-2017, 12:40:04 PM   #40
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Default Re: Getting Gas with the Engine Running

Half the time I leave the car running when I fuel. I never let the car get low and I never top it off. I work for a gas station company and sure, there are signs about it being illegal, but from years of being in the business, the employees don't care. No one is getting arrested
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Discussing Getting Gas with the Engine Running in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)