Hey guys.. rookie question again.. I drive about 200 miles a day 6 days a week. I make five 10 minute stops a day and five 20 minute stops a day. I'm near the van the entire time, so theft is not an issue. When I had my gas vans I always turned them off during the stops, but I've read that with diesels you should leave them on. (this seems counterintuitive to me, one of the reasons I bought the diesel was to save money on gas)


Any suggestions?


Thanks!!!


Neil

So, 10 times a day off and on vs. letting it Idle 2.5 hours or so.


6.5's may have low oil pressure at idle, or so I read on diesel automotive services web site. I would think your starter should be able to handle 10 times.

6.5 @ idle uses approx 10cm(3) fuel per cylinder per 1000/strokes. So lets assume yours idles 2.5hrs @ 650RPM


2.5HRs * 60min/hr = 150 minutes * 650R/M = 97500 revolutions Divide this by 2 because were talking about a 4 stroke motor that only fires on half these revolutions, and multiply by 8cyl you get 390000 injections in 2½ hrs of idle. divide by 1000 strokes and multiply by 10cm to get total fuel delivered: 3900cm(3) which equals ~1.03 gallons. So for about a gallon to idle for 2.5hrs you can save your starter 10 additional starts a day and the engine will stay warm ready to go when you are.


Think of it like a flourescent lightbulb, leave it on, it doesn't use much power to run all day, but flip it on and off and your use a lot more power and the ballast(starter) will go out on you quicker.Edited by: Texas Diesel Guy

hmmmm... not to sure on those numbers TDG. I work out of my truck most of the time and would have to say that i burn 50% of my tank on high idle of about 1100 rpm, small tank in the short box, can't remember the gallons it holds. Probably 10 hrs idle time too.

1100 RPM loaded your talking about nearly double the speed and triple the fuel delivery and you will certainly use more fuel that way, roughly 6 times as fast as at L.I.

Okie dokie...


Maybe i'll stick to making pictures. lol

6.5 @ 1100RPM and lets say about 25cm(3) delivery rate.


150 minutes * 1100R/M = 165000 revolutions x 8cyls / 2 (4 stroke) = 660000 injections x 25cm(3)/1000 strokes= 16500cm(3) which equals ~4.36 gallons in 2.5hrs or ~17.4 in 10hrs. Sounds about right? 1/2 tank is about 15 gallons.


So its roughly 4x the consumption rate compared to L.I.


Note: corrections made to earlier calculations, its cm(3) not mm(3)Edited by: Texas Diesel Guy

Texas,


So you are saying i'm burning 4.36 gallons by leaving it on? It seems a no brainer then at $1.83 a gallon to turn it off. That would calculate out to about $2500 in additional fuel costs per year. How many starters can I buy for $2500? (lol)

TDG is refering to fast idle of 1100 rpm uses 4.36 US gal. normal 650 idle uses 1.03 gallons for the same time period. Edited by: quantum mechanic

6 days a week 52 weeks 2.5hrs a day, and one gallon per 2.5hrs is about 300 gallons a year on idle fuel, and if your paying $1.83 a gallon (yikes) its more like $550 annually, which is more expensive than a starter. But as I said, this estimate is probably on the high end, I know mine only idles @ 560 and uses less than 10cm fuel to maintain that, which would put me just under a gallon every 3hrs. If thats the case with yours, then your talking about ~$475 annually. Not to mention a burnt out starter will cost you time and maybe towing and shop bills as well. Edited by: Texas Diesel Guy

You can buy 10 starter for that 2500.00 but you have to pay someone to put them on, @ say 75.00 each. add that 750.00 to the cost, plus, and I speak from my experience, bad starter equal bad battereies and at least one alternator so I'm betting thaose or another 500.00 or so installed. I woul never knowingly add 10 or so more start events to my starter system period. My diesel's have idled for hours, sometimes at one time in ALaska with the temp's hoving at -40 to -50 below zero.

Bowtie, he misread my earlier posts, 2500 would be enough for him to idle for 5 years.

TDG


1st Glad to see U here again. http://www.dieselplace.com/forum/smileys/Hug.gif


2nd I was just anwsering the question asked. LOL


and I didn't throw out there the headaches involved with starter going out.

You know, I was just going to ask that question about idle and fuel consumption. I was wondering about high idle fuel usage for my a/c to run.

how fast of a high idle are we talking about? you mean when they truck automatically increases idle when the A/C is on?

It's a bus with a high idle controller. The controller bumps up the idle upon voltage drop on the system (to run a/c handicap lift, lights, etc.) It has a manual engage to 1200 rpm.


My a/c is a disaster setup at the moment, and contemplating how best to address the upgrade. My question about fuel consumption was seeing about letting the thing idle when I was in church for an hour keeping the bus cool, as compared to what I would spend in upgrading a/c. Long, long story, with much research yet to do.

I could only make a guess, but I would think that an alternator load alone and the increase from CR's 1100 to 1200 would put you at nearly the same 1.74 Gallon per hour consumption rate.

10mm of fuel at idle? Is that the number that shows on a scanner? I seem to remember mine taking 3mm with the AC off and 5 with it on. I might check it tomorrow just to see since it has been a while since I looked at it.

Scanner is not the best method for determining fuel delivery at idle, On the test bench, A DS pump calibrated exactly to spec, will deliver approx 13-15cm at 600 RPM L.I. This is too much fuel and the onboard computer on the truck has to use less than that to maintain idle speeds and really doesn't have a clue how much fuel its actually being delivered. 12-14 is where the mechanical 6.5 pumps are calibrated to @ L.I. of 600-650. Trust me, the actual amount of fuel in an electronic 6.5 is between 9-12cm at L.I. forget what the scanner tells you. if you were only using 3cm, you could idle for a month straight.

Maybe someone else with a scanner can check. My truck isn't quite righthttp://www.dieselplace.com/forum/smileys/Cry.gif

did you tell me earlier that you did the optic adjustment on your truck? that would certainly account for the really low reading, but a 6-9 delivery at idle according to the scanner is normal.

Last time I looked on mine it was .10-.20" at idle but this was old ECM, I'll check it again and change the setting back to metric. Also I was going to try and bump my optical just a little more. I've not had a chance to set it since I upgraded to the 95 controls. I think it went from 8 to 12 mm at idle when I did the bump with the 5068 setup.Edited by: quantum mechanic

A friend of mine works as a bus mechanic on Cummins and he encourages the drivers to idle between stops and idle down the turbo temp for at least 5 minutes at the end of the day.

Idea being to cool down the components and avoid as much heat soak into turbo and electronics as possible.

I would imagine that the 6.5 is similar in this area. Wouldn't this be a good reason to idle during short stops, even if it does use a bit more fuel?

Dave

I let mine idle a bunch. As an engineer, I realize that most systems have the lions share of problems when they changes states. Going from cold to hot, start to stop, engaged to disengaged, etc. is when things fail.


Have you ever seen a lightbulb that has been on for more that a few minutes just burn out? Me neither.



Tim

did you tell me earlier that you did the optic adjustment on your truck? that would certainly account for the really low reading, but a 6-9 delivery at idle according to the scanner is normal.





No, I never got around to opening it up. I was just asked if you thought could have moved on it's own.