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| Crazy CRD mileage http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=10544 |
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| Author: | huxrules [ Mon Jul 17, 2006 11:13 pm ] |
| Post subject: | Crazy CRD mileage |
Hello all- I have just returned from a weeklong road trip through the southwest. I have noticed something very strange about my mileage. Overall the CRD delivered 22.4 mpg. The high peak was 26.34 and the lowest was 20.51. I measured the mpg with the "fill the tank" method. My data showed a trend- I get worst mileage at home then I do in the mountains. My best mpg was between Durango,CO and Albuquerque, NM (26.34). My second best tank was between Albuquerque and Clarendo, TX at 25.5mpg. The third best was between Oracle, AZ and Durango at 23.3. All these tanks had a mix of biodiesel. Most tanks are just highway driving at "posted + 5" so about 75 – 80 mph. The weird thing is that I thought the crd was acting like at dog at the higher altitudes- but it delivered a better mpg. Where I live (at about 100ft above sea level) I regularly get 20 mpg. In what crazy world do we life in where you get worse mileage at sea level? Did they program this diesel to run to perfection in the high alps? What do you guys think? HUX |
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| Author: | DarbyWalters [ Mon Jul 17, 2006 11:28 pm ] |
| Post subject: | |
Thinner Air...less fuel delivery...a little less power |
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| Author: | KJ-BOL [ Mon Jul 17, 2006 11:34 pm ] |
| Post subject: | |
DarbyWalters wrote: Thinner Air...less fuel delivery...a little less power
True... mine sucked big time going up from Denver to Vail Pass - I was seeing minivans going faster then me.... 
gas mileage suffered & power suffered even worse BTW - mine is not a CRD - but still... |
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| Author: | IndyCRD [ Mon Jul 17, 2006 11:35 pm ] |
| Post subject: | |
Same thing happened to me just recently. I calculate my mileage at every fillup and I always get about 22 or 23 mpg. A couple of weeks ago I went on vacation to the Blue Ridge mountains in NC. I got 26.5 on that trip with all that mountain driving. That's record mileage for my CRD. |
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| Author: | huxrules [ Tue Jul 18, 2006 12:17 am ] |
| Post subject: | |
I guess I should clarify. I had less power in the high altitude enviroment- until the turbo spooled. There is less air up there- therefore less power- and a heavier foot on the pedal (possibly). But with that- how could I have gotten better (much better) gas mileage? Strange I say. Am I running rich at sealevel? Could the thinner air actually made that much difference with the aerodynamics? HUX |
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| Author: | Cowcatcher [ Tue Jul 18, 2006 12:32 am ] |
| Post subject: | |
You can't get it out of impulse and into warp drive under about 3000 feet above sea level. Warp is much more energy efficient. |
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| Author: | Hero [ Tue Jul 18, 2006 1:52 am ] |
| Post subject: | |
Its called "Forced Induction" aka Turbo, the turbo forces air into the engine and compresses it. I'm no scientist by any means, but my most generalized conception is that since you were feeding thinner air into your engine (but still more than an N/A vehicle) you'd be using less fuel while still being able to get more power than the average N/A vehicle. I live in the plains of Illinois and cannot get over 23 MPG no matter what I do, I think that humidity may have something to do with it as my area typically has far more moisture than most of the country... I won't say I'm right on any account, these are just my assessments 
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| Author: | Special Agent [ Tue Jul 18, 2006 9:49 am ] |
| Post subject: | |
The notion of "thinner air" is sort of off... Air pressure is lower at higher altitudes, but the Turbo is an air compressor... The question becomes: How does the lower outside air pressure affect the engine's pressure? One obvious possibility is that the engine's pressure specs are unchanged thanks to the turbo, but the reduced backpressure on the tailpipe increases fuel effeciency??? Or maybe the engine pressures are lower during the exhaust cycle because it vents and equalizes to the outside pressure, which then assists the high-pressure common rail in atomizing the fuel??? Is atomization assisted by a greater variance of pressures between cyliner/injector??? Just some thoughts... Not a gearhead or a scientist!!! LOL! |
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| Author: | Cowcatcher [ Tue Jul 18, 2006 10:34 am ] |
| Post subject: | |
OK, I think it is none of the above. I think your driving style changes inperceptibly when you travel and I think those who really think they are getting their fuel tank filled to the same level each time are also smokin' funny cigarettes. 
One definate thing is the CRD likes......no, LOVES!!! to get on the road and roll and it reflects that in MPG. No matter how you drive each day it is not quite the same as when you travel regarding stop and go etc. When you travel you typically spend 2 or more hours at a stretch without stop and go and that is when the CRD shines despite elevation or climbs. Next week I drive cross state. I am one of those guys that likes to power up and go and I likely will not stop in the first 250 miles when I stop to get my first tank of B99. I bet I get over 30 MPG on the EVIC before I add the 7% odometer error! |
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| Author: | DarbyWalters [ Tue Jul 18, 2006 11:03 am ] |
| Post subject: | |
It could be like a Turbo Prop...very efficient when cruising speeds are met at high altitudes. The turbo gives you a better power to fuel ratio than normally aspirated and burns less fuel than at lower elevations. |
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| Author: | alljeep [ Tue Jul 18, 2006 11:43 am ] |
| Post subject: | |
Cowcatcher wrote: and I think those who really think they are getting their fuel tank filled to the same level each time are also smokin' funny cigarettes.
The only time I top off is to test MPG. I get about 2.1 gallons after shut off and the fuel is pooling in the top of the filler neck opening with no level dropping down. That extra 2.1 gallons can take 15 extra minutes at the pump to get it in - literally - it's a pain - but a huge effect on calculated MPG if your off by 1-2 gallons each time you fill up. |
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| Author: | oldnavy [ Tue Jul 18, 2006 11:59 am ] |
| Post subject: | |
DarbyWalters wrote: It could be like a Turbo Prop...very efficient when cruising speeds are met at high altitudes. The turbo gives you a better power to fuel ratio than normally aspirated and burns less fuel than at lower elevations. That is oh so correct and is where the turbo was first used on diesel trucks with great sucess. Peterbuilt trucks made their name for being able to carry more and go faster in and over the mountians of the western US back in the early days of US trucking industry when so few other trucks had turbo's on the engines.
Also when traveling there can be great difference in fuel you buy, the engine also cleans itself out from injector tips to exhuast tip and starts getting better fuel mileage. |
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| Author: | vtdog [ Tue Jul 18, 2006 1:05 pm ] |
| Post subject: | |
My experience is that the mileage calculation is most effected (or is it affected-never can remember) by the fill level of the tank. I have noticied that fills with the "large" nozzle seem to cut off earlier than those with the "car" size filler nozzle. I suspect that you can get in an additional gallon or so with the smaller nozzle as there seems to be less foam due to lower outflow which allows the pump to run longer before cutoff. The addition of the "extra" gallon at fillup can greatly change ones mpg. |
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| Author: | huxrules [ Tue Jul 18, 2006 2:12 pm ] |
| Post subject: | |
from old navy: Also when traveling there can be great difference in fuel you buy, the engine also cleans itself out from injector tips to exhuast tip and starts getting better fuel mileage. From me: I agree but my mileage has slipped back to it's normal 20 mpg. As for better fuel you might be correct I guess I'll never know. Has anyone else seen good mpg with Blue Sun bio? That's what I was using. My last tank of the trip was actual ULSD from exxon. That should be some super juice- but I only got 22 mpg. As for the turbo I guess I'll just have to get a boost meter to see if the turbo produces the same amount of boost at high altitudes as it does here. Do you think the turbo will actually spin faster at higher altitudes to acheive the same boost? I guess I'll just have to move to Durango so I can enjoy the better mileage in my CRD. If it just weren't for all those silly mountains getting in the way of the view! |
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| Author: | BiodieselJeep.com [ Tue Jul 18, 2006 4:06 pm ] |
| Post subject: | Don't forget that sweet spot |
the Brake specific whosawhatsy is best at very close to 2000 rpm = 68 mph. Those with more geek cred than me say that's the spot to be in. Recent tests were: 23 mpg last year, medium load, 100% dino Highway trip @75mph++ 20.5 mpg on 100% Bio with my wife driving in the burbs (And she rides it like both brakes and fuel are free). 21.8 mpg on memorial day trip at 75 mph (2200rpm) plus some mountains, 100% Bio, seriously loaded with hitch rack. 25.7 mpg last weekend at 68 mph (2000 rpm) going to the beach, medium load, 10%Bio Big big jump at 2000 rpm. I bet you were a lot closer to 2000 rpm in the mountains. Check it out next higway trip. |
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| Author: | oldnavy [ Tue Jul 18, 2006 4:14 pm ] |
| Post subject: | Re: Don't forget that sweet spot |
BiodieselJeep.com wrote: the Brake specific whosawhatsy is best at very close to 2000 rpm = 68 mph. Those with more geek cred than me say that's the spot to be in. Recent tests were: It is amazing what a drop in mpg when go past 2000/2100 rpm. You are looking at a 25% or better differential depending on fuel, load, weather and alittude just going from 65 mph to 75 mph. I think it is almost all due to aerodynamic's.
23 mpg last year, medium load, 100% dino Highway trip @75mph++ 20.5 mpg on 100% Bio with my wife driving in the burbs (And she rides it like both brakes and fuel are free). 21.8 mpg on memorial day trip at 75 mph (2200rpm) plus some mountains, 100% Bio, seriously loaded with hitch rack. 25.7 mpg last weekend at 68 mph (2000 rpm) going to the beach, medium load, 10%Bio Big big jump at 2000 rpm. I bet you were a lot closer to 2000 rpm in the mountains. Check it out next higway trip. |
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| Author: | rs4mtnitro [ Tue Jul 18, 2006 7:47 pm ] |
| Post subject: | |
Special Agent wrote: The notion of "thinner air" is sort of off...
Air pressure is lower at higher altitudes, but the Turbo is an air compressor... The question becomes: How does the lower outside air pressure affect the engine's pressure? One obvious possibility is that the engine's pressure specs are unchanged thanks to the turbo, but the reduced backpressure on the tailpipe increases fuel effeciency??? Or maybe the engine pressures are lower during the exhaust cycle because it vents and equalizes to the outside pressure, which then assists the high-pressure common rail in atomizing the fuel??? Is atomization assisted by a greater variance of pressures between cyliner/injector??? Just some thoughts... Not a gearhead or a scientist!!! LOL! I saw someone post on here one time that a cold air induction would make no difference on a turbo vehicle and I say bs and I feel the same way about thinner air not making a difference. The more free flowing air you get to the compressor equals more air to compress. That is why on staged twin turbos the first turbos charge air is blown into the second turbos intake. That in effect compresses the already compressed air even more. The thinner the air, the less exhaust there is to spin the turbo. If the boost is lower it will use less fuel. |
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| Author: | naturist [ Tue Jul 18, 2006 8:06 pm ] |
| Post subject: | |
Um, guys, I've looked into this, and on both the CRD and the VW TDI, the turbo and ECU are designed to supply air to the engine at an absolute pressure, rather than a relative one. What this means technically is that at the intake valve, the pressure will remain constant relative to the load regardless of altitude, within the turbo's ability to compress it. Thus theories about improved mileage due to thin air are working on a bogus assumption: as far as the engine is concerned, there is no such thing as altitude. The turbo just works harder as you go up. |
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| Author: | oldnavy [ Tue Jul 18, 2006 8:16 pm ] |
| Post subject: | |
rs4mtnitro wrote: I saw someone post on here one time that a cold air induction would make no difference on a turbo vehicle and I say bs and I feel the same way about thinner air not making a difference. The more free flowing air you get to the compressor equals more air to compress. That is why on staged twin turbos the first turbos charge air is blown into the second turbos intake. That in effect compresses the already compressed air even more. The thinner the air, the less exhaust there is to spin the turbo. If the boost is lower it will use less fuel.
The cold air inductions (cone crap under hood) sold to most buyers will show no hp/tq incrase on dyno, where true a cold air (usually called and intercooler) will, these cheap cone things only help N/A gassers. Seen the dyno numbers before. Correct on the thin air thing, the turbo has to spin faster to get in more air (ak O2) and at some point when not enough O2 for even the turbo ignition stops. This effect is at much lower alittude with NA engine. Less boost doesn't mean less fuel equals better mpg's, it can mean several things. Loss of turbo power means BIG drop in power and lower mpg as many diesel car owners can speak about, in proper working turbo and IP less boost can mean better mpg's. At sea level a turbo pull all the air it needs without any fancy intake work or ducking unless you be racing and are concerned with 1/100 or 1/1000 of second at the finish line. On a stock street machine like our you could not tell the difference in daily use. If however you have changed out the stock exhuast, chipped and changed injectors to larger size, then the change away from stock intake and filter is needed. This is very abreviated but will give you an idea where I am coming from. |
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| Author: | Joe Romas [ Wed Jul 19, 2006 7:15 am ] |
| Post subject: | |
huxrules wrote: I guess I should clarify. I had less power in the high altitude enviroment- until the turbo spooled. There is less air up there- therefore less power- and a heavier foot on the pedal (possibly). But with that- how could I have gotten better (much better) gas mileage? Strange I say. Am I running rich at sealevel? Could the thinner air actually made that much difference with the aerodynamics?
HUX I think what's going on is at highter elevations with less air pressure there's less air flowing by the mass air flow sensor and the computer therefore gives less fuel. That in turn gives better MPG. Untill you put your foot into it and get the boost up. With the reverse true at sea level (more air, more fuel=more power):cry: Remember the CRD's are a drive by wire engine and the computer is totally controlling it 
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