Question about the math for EOC vs Coast?

[Tygen1]

I've been trying to figure out what the benefit of EOC is without actually trying it.
The math I have done is based on my commute. 400 miles a week, average speed is 45 mph and my last three tanks average is 40.45mpg which approximatly equals a GPH of 1.11.
I Coast with my engine on for approximatly 10% of my one hour drive (6 min.). My normal GPH while coasting has been 0.22. So If I subtract the gallons of gas saved via. coasting (0.22gph vs. 1.11gph) then the mpg if I didn't Coast would be 36.9mpg and my average gph would be 1.22.
So lets say for the same 10% of time driving my engine is off (0.22gph vs. 0.00gph), then my mpg would be 41.56 vs 40.45 that I am currently at.

To sum up the math, if it is correct. It seems that Coasting benefits me by 9% and EOC could benefit 11%, or just 2% better than Coasting.

Does any of this make sence? It seems correct to me?

[moonmonkey]

you also use a little gas on restart ,dont forget to factor wear and tear on starter/flywheel ,,your math makes sense,, to me though.

[RobertSmalls]

Your math seems sound to me as well. I say it's pretty clear: you burn a gallon of gas a week idling. Install a kill switch and pick up that slack! You'll save $150/yr.

Besides, it's very relaxing to turn off your engine and roll up to a red light with no noise other than that of your tires. It also removes the pressure to get away from the light in a hurry, since you're burning zero fuel sitting there.

[Tygen1]

My starter is a hit and miss unit right now, when that is addressed I intened to expirement with the idle issues. I need to track the time idleing up to and at stop lights and do some math. I have about 12 stoplights each way going to and from work. So that is 120 stops a week and the associated idle time. I currently coast up to stop lights.

I thought it was interesting that EOC is only slightly better than Engine On Coasting. So I guess ATX's don't suffer as much as I previously thought.

[Old Mechanic]

Do you have to stop at every light?

My daily trip is close to 52 lights, but I seldom have to stop for more than 6, sometimes less than that.

I agree that enigne off coasting can save you money in fuel, but I think it might cause you to have other repairs that offset the savings.

In my VX lean burn is disabled for something like 30 seconds on every restart so it will not help me to do EOC in the VX.

regards
Mech

[Tygen1]

I commute thru Philadelphia and on congested roads, I do my best to minimize stopping, timing lights and such. The number of stops is an average, I pass thru many more stop lights, that's just the number of times I usually stop.

I'm not too concerned about EOC causing any undue repairs. I've already got 265,000 miles, so there's plenty of time spent PM'ing this car anyhow. I have a set budget and can opperate within it pretty well and have enough latitude for major repairs if they arise. I also do all the work myself and that saves a tremendous amount of money. I also shop at the U-pull it yards for parts off good wrecks.

Maybe I'll work on a spread sheet to calculate the wasted gas/potential improvement from not idling at stop lights. I've made an eccel spread sheet for the EOC vs. Coast. If I can refine it a bit with real world results I think it could be helpfull in further refining my commute and where the best times to coast or keep the power on.

Also, is this picture some sort of record for Idle GPH in a gas motor I'm amazed at how low the idle gph can go under the right circumstances...

[Tygen1]

Ok, I calcultated that if my average Idle Time at a stop light is 30 sec, 24 stoplights per day and 0.22 gph. Then that would be 1 gallon of fuel per week. If I were to turn the motor off instead of idling, then that would be a 1mpg gain or 2%. I believe these numbers are high, I will have to take a stop watch with me for a couple days to see what the actual is...