"Cartalk" just announced gas saving tips - GreenHybrid

rigger · #1 (**permalink**) 10-30-2005, 03:50 PM

....on their web site. Stuff WE already know for the most part.

Car Talk Gas Saving Tips

Still interesting. They mentioned it when someone called in to ask about drafting. They didn't recommend because it was too dangerous. My wife was in the car when they said it.

Now I'll never hear the end of it.

tbaleno · #2 (**permalink**) 10-30-2005, 03:53 PM

drafting is dangrous? What about carrying 11 gallons of high explosive liquid 4 feet from your body? Heh

rigger · #3 (**permalink**) 10-30-2005, 03:58 PM

I have seen rigs toss up "gators" before so I see where they are coming from. They also mentioned the delayed reaction time.

Still, I wouldn't of made it across Texas one time on my motorcycle if I hadn't drafted. Had a 35 miles per hour crosswind and I could barely stay on the road. Pulled in behind a double trailer 18 wheeler and drafted my way for about 150 miles. He was a lifesaver and he knew exactly what I was doing and why.

coyote · #4 (**permalink**) 10-30-2005, 07:00 PM

Q: How many hybrid owners do you suppose would be complaining about their "poor" MPG if they followed these simple tips from CarTalk?

A: None.

xcel · #5 (**permalink**) 10-31-2005, 06:37 PM

Hi Coyote:

Q: How many of those same Hybrid drivers would receive far more FE after spending just a day or two catching up on what we talk about here?

A: All

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

lkewin · #6 (**permalink**) 11-01-2005, 08:31 AM

One of the tips in the article is to "Stop your Idling", which raises a question I have had, but because I am a guy, could not let me wife see me ask!

She is not on-line, so I will sneek the question in

Quote:

Originally Posted by article

Some people have heard a myth that it takes more gas to start a car than to run it. ... It's complete B.S. If you're stationary for more than a couple of minutes, shut it off, and save gas.

How are Hybrids diffrent then non-hybrids (NH) when it comes to saving fuel by shutting the engine off...even if for just 15 or 20 seconds while you wait for the red light to turn green?

I have seen some heavy formula's thrown around in other threads and know we have a few rocket scientists in our midst, so.. is there a way to calculate the amount of time you would need to shut off the engine of a NH to overcome the "penalty" to re-start....or is there not more gas used to start an ICE?

hawkGT647 · #7 (**permalink**) 11-01-2005, 09:55 AM

Quote:

Originally Posted by lkewin

I have seen some heavy formula's thrown around in other threads and know we have a few rocket scientists in our midst, so.. is there a way to calculate the amount of time you would need to shut off the engine of a NH to overcome the "penalty" to re-start....or is there not more gas used to start an ICE?

I would think that shutting off the engine and restarting would not use more fuel.
The only time it uses more fuel is if the engine cools completely and goes into a cold start mode (enrichen the mixture).

I watch the ScanGauge on my wife's Acura TL just go down, down, down while idling at a long traffic signal.

Very discouraging after working hard to build up the trip MPG. I shut it off at traffic signals that are known offenders, but at short stops I leave it running. I don't want to wear out the starter!

Her car will average 26-28 mpg in steady moving city driving, it's the stops, idling, and getting back up to speed that kills the mileage, then it's averaging 23-24 mpg at best.

Regards,

gonavy · #8 (**permalink**) 11-01-2005, 11:34 AM

Quote:

Originally Posted by lkewin

I have seen some heavy formula's thrown around in other threads and know we have a few rocket scientists in our midst, so.. is there a way to calculate the amount of time you would need to shut off the engine of a NH to overcome the "penalty" to re-start....or is there not more gas used to start an ICE?

OK, I'll venture in:
assuming a warmed up engine, stoichiometric burning and 13:1 mass air/fuel ratio at sea level (fuel @ .75g/cc and air @ .0012g/cc)...approx. 8000:1 air/fuel volume ratio.

A 2 liter engine at 700rpm idle speed injects ~.125cc of fuel every rotation (1 injection per cylinder every 2 rotations for 4-stroke engine, so 1 liter "active" per rotation)

ASSUME it takes about 2 sec to start the engine to idle, and ASSUME that the mix is enriched and nonstoichiometric (=smelly emissions at startup), so ASSUME it uses triple the fuel for those 2 seconds. 3 x .125cc x 25rotations = ~9.5cc of fuel to start the engine. Call it 10. That's 2 teaspoons.

Back at normal idle, the engine will use 2 teaspoons of fuel in 80 rotations, or 7 seconds.

There you go. Idle for more than 7 seconds and you are better off stopping and restarting. Call it a bullride- 8 sec. Or 10 for us cityslickers.

Schwa · #9 (**permalink**) 11-01-2005, 03:32 PM

I've heard 15 seconds may be the optimum amount of idle time before it's worth, or rather to be worth it... You have to take the power the starter uses that gets replenished when the engine runs into account as well. But 10-15 seconds is all it really takes for smaller vehicles.

rigger · #10 (**permalink**) 11-01-2005, 04:28 PM

That's about what I do Schwa. When driving my HCH and I am nearing a light that I "know" will change very soon I downshift into "S" right before I stop. This interrupts the Autostop.