Mileage question

Hjalti · **Posted:** Sat Jan 12, 2008 7:32 pm

Hello

The winter urban mileage I have experienced from my 2006 CRD is rather poor in my opinion. While driving around town it has been burning 16-19 l/100km (12-15 MPG). This is mostly short trips, using fulltime 4wd most of the time, temperature around zero celcius. During summer 19-23 MPG urban, highway mileage is fine, 24-29 MPG. It has 14.000 miles, 1.5" lift and 255/70 studded tires, has not had any flashes, have already cleaned the MAP sensor and tried fuel additives (from Comma and QMI). I have always understood that diesel mileage fluctuated less between summer/winter and urban/highway than I have experienced so far with my Liberty.

Do you have any suggestions or is this maybe normal :roll:

?

Joe Romas · **Posted:** Sat Jan 12, 2008 8:45 pm

Winterized diesel has less BTU's so your mileage goes down :cry:

warp2diesel · **Posted:** Sun Jan 13, 2008 12:18 am

Add these facts to Joe's:
1) Oil is thicker and eats up more power.
2) Tires role with more resistance and loose air faster due to more bumps and unforgiving rough pavement.
3) Oxygen level in air is lower.
4) Engine takes longer to warm up resulting in lower efficiency.
5) Snow and other winter debris increase rolling resistance even more.

Look on the bright side, our Liberty CRDs are Jeeps :!:

Steve

DarbyWalters · **Posted:** Sun Jan 13, 2008 12:37 am

Born in Keflavik myself

I get 10.5-10.6L/100km winter city/combined but I am in South Texas now. Unless you get to temp quickly, your mileage will suffer...are you plugged in at night? Maybe a Grill Block would help you?

http://s205.photobucket.com/albums/bb97 ... P_0209.jpg
Drag your sursor across the Grill...You couls probably get away with blocking all 6 (leave the one that give you air intake) and get better mileage.

Uffe · **Posted:** Sun Jan 13, 2008 5:04 am

warp2diesel wrote:

Add these facts to Joe's:

3) Oxygen level in air is lower.

All valid points, but number three I have to correct.

When it becomes colder more oxygen exist in the same amount of air because the air becomes denser. This is a two-edged sword because when the air becomes denser the resistance you drive through increases. From 0C to 25C there is a 10% increase in the drag you experience. As your speed increases the energy in the air increases to the power of three.

warp2diesel · **Posted:** Sun Jan 13, 2008 1:09 pm

Plants that use CO2 for photosynthesis produce oxygen. When it gets cold most plants go dormant and the ones that don't, slow down considerably. True the air becomes more dense but the percentage of oxygen in proportion to the nitrogen is lower.
Since our Liberty CRDs do not have a thermostatically controlled intercooler bypass to prevent over cooling the intake air under cold weather conditions, Darby Walters has the best recommendation to increase winter fuel economy.

Steve

artickid · **Posted:** Sun Jan 13, 2008 1:12 pm

What is the optimal mainfold air temp for our Jeeps. I have been using a scanguage and with the ORM I have been seeing 60-70f air temps and without the ORM I have been seeing 110-130f temps. Ambient outside temps have been between 0-35f.

retmil46 · **Posted:** Sun Jan 13, 2008 1:33 pm

Add cold fuel into that as well. On the return leg of my recent trip, covering over the fuel cooler and allowing some heat to build up from return fuel flow to the tank made almost an 8 MPG difference in fuel economy (from 22 up to 30) once the fuel in the tank had warmed up.

The ECM does adjust fueling based on the reading from the fuel temp sensor (along with engine coolant temp). Making short trips, along with the engine not really getting warmed up, you're probably not getting enough return fuel flow back to the tank to warm it up to the "goldilocks" temp range.

This beast is like Goldilocks and her porridge when it comes to engine and fuel temps - not too hot, not too cold, it has to be just right. :lol:

warp2diesel · **Posted:** Sun Jan 13, 2008 2:33 pm

Back in the days when any Diesel polluted less than a gasoline engine even with black smoke rolling out due to no carbon monoxide emissions. I had some Dyno engineers show me that the perfect air intake temp for a Diesel engine is 60f (15c). Agricultural tractor manufactures would advance or delay the introduction of new models so they could do the Nebraska Tractor Test at as close to 60f as possible. This would provide the peak performance and fuel economy which was measured in Horse Power Hours per Gallon. Any mechanical adjustments or repairs were noted and the manufacturer could elect to let the test stand or withdraw and not sell any tractors in Nebraska until they passed the test. One year John Deere had their foot throttles stick and had to lube the linkages, John Deere got out the oil can and accepted the tests.

I have seen thermostatically controlled lovers on the front of some large over the road trucks and some Volvo industrial engines use thermostatically controlled inter-cooler bypass circuits to keep the intake air at an optimum temperature, but Darby still has the best idea so far. Some how mounting a Mack truck grill with lovers on the front of a Liberty would look a little too tacky for me.

Fuel temperature control looks very interesting to me and could be a doable option. Does any one know what the Goldielocks fuel temp is?

Steve

retmil46 · **Posted:** Sun Jan 13, 2008 3:07 pm

warp2diesel wrote:

Fuel temperature control looks very interesting to me and could be a doable option. Does any one know what the Goldielocks fuel temp is?

Steve

Well, I can tell you from recent experience that it sure as h### ain't 20 F! :lol:

Best guess for the lower limit would be 80 to 85 F. That seems to be what nearly every fuel filter heater I've seen (including the heater on our stock fuel filter setup) is set to turn off at.

Upper limit? Based on what was related here many moons ago about some testing Detroit Diesel did back in the 80's, perhaps 120 F. Any higher than that, and you're flirting with the vapor point of diesel fuel (where it can start forming combustible vapors), which can be anywhere from 125 F to 140 F depending on how it's blended.

My best guess would be somewhere around 100 F. After covering over the fuel cooler and running for 180 miles down to 1/4 tank, ambient temp around 30 F and fuel mileage hitting back up toward the 30 mpg mark, when I pulled in for fuel I popped the hood to check things out before shutting it down. Fuel filters felt at least body temp if not warmish, and I was reading full lift pump pressure downstream of both filters (Stanadyne 30 micron and Cat 2 micron).

DarbyWalters · **Posted:** Sun Jan 13, 2008 10:12 pm

Two points I and others overlooked. 1) Your viscous heater will be working overtime and hurt (minnka) short trip mileage...and 2)Your tranny will operate differently until it comes to temp. I guess the combination of these and cooler temps in general could easily lower MPGs.

MrMopar64 · **Posted:** Sun Jan 13, 2008 11:33 pm

retmil46 wrote:

warp2diesel wrote:

Fuel temperature control looks very interesting to me and could be a doable option. Does any one know what the Goldielocks fuel temp is?

Steve

Well, I can tell you from recent experience that it sure as h### ain't 20 F! :lol:

Best guess for the lower limit would be 80 to 85 F. That seems to be what nearly every fuel filter heater I've seen (including the heater on our stock fuel filter setup) is set to turn off at.

Upper limit? Based on what was related here many moons ago about some testing Detroit Diesel did back in the 80's, perhaps 120 F. Any higher than that, and you're flirting with the vapor point of diesel fuel (where it can start forming combustible vapors), which can be anywhere from 125 F to 140 F depending on how it's blended.

My best guess would be somewhere around 100 F. After covering over the fuel cooler and running for 180 miles down to 1/4 tank, ambient temp around 30 F and fuel mileage hitting back up toward the 30 mpg mark, when I pulled in for fuel I popped the hood to check things out before shutting it down. Fuel filters felt at least body temp if not warmish, and I was reading full lift pump pressure downstream of both filters (Stanadyne 30 micron and Cat 2 micron).

The heater on the KJ never shuts off since it is unfortunately not controlled by the ECM. Key on = heater on, pretty simply control (haha). The fuel temp sensor is used to form the protection strategy for the high pressure pump - as the fuel temp crosses a certain threshold, it will begin to limit the fuel flow through the pump/rail/in-cylinder injection and thusly engine torque so that the fuel temps will begin to drop.

As for the intake manifold temps, there is a similar strategy surrounding the air temp sensor in the manifold. Injected fuel quantity is clipped once a certain threshold is reached so that turbocharger speeds are limited thus limiting boost pressures and consequently lowering engine output so that the intake temps stabilize. Generally this limitation is never reached before that for the coolant temp protection is which is much more severe to prevent overheating of the engine.

warp2diesel · **Posted:** Sun Jan 13, 2008 11:50 pm

Does the ECM sense if the fuel heater is on or not :?:

If not why can't we shut off our heaters when the fuel temp is at the optimum temp :?:

I have a new in box Pollock 6 port fuel selector valve that can be used to send the return fuel to a fuel cooler when it is over a set temp :idea:

A simpler set up would be to rob a wax element out of a cooling system thermostat, recalibrate it and have it activate a three way valve that either sends the fuel to the tank or a fuel cooler. :idea:

Steve

retmil46 · **Posted:** Mon Jan 14, 2008 1:00 am

warp2diesel wrote:

Does the ECM sense if the fuel heater is on or not :?:

If not why can't we shut off our heaters when the fuel temp is at the optimum temp :?:

I have a new in box Pollock 6 port fuel selector valve that can be used to send the return fuel to a fuel cooler when it is over a set temp :idea:

A simpler set up would be to rob a wax element out of a cooling system thermostat, recalibrate it and have it activate a three way valve that either sends the fuel to the tank or a fuel cooler. :idea:

Steve

Actually, what the FSM says is that the stock fuel heater is constantly supplied with power, but that the material it's made out of will (supposedly) drastically increase it's electrical resistance when the fuel gets up to 80 to 85 F, such that it essentially isn't pulling any power and shuts itself off.

Yeah, and there's a lot of people with fried harnesses and melted heater pucks to attest how well THAT idea works. :roll:

Nothing to keep you from wiring a separate thermostat in the harness for the stock heater to turn it off at the appropriate temp. Or there are fuel heaters with built-in thermostats that are small enough to plumb iinto the fuel line ahead of the stock filter (ie, Stanadyne pencil type fuel heater)- just disconnect power to the stock heater and reroute the harness to your new thermostat-controlled heater.

FWIW, one of the Stanadyne pencil type heaters is only about $20, and you can pick up the plumbing parts to make it's own in-line housing at your local hardware store.

I've been thinking of the same idea, a temp controlled method of automatically routing return fuel flow to the tank either thru a fuel cooler, or bypassing it, depending on fuel supply temp to the filter (which should be basically equivalent to fuel tank temp). But that's the trick - you need to be sensing fuel temp in the fuel SUPPLY line to operate an automatic valve in the fuel RETURN line. Or alternately you could sense fuel tank temp (which is going to determine fuel supply temp to the filter) and use that to control the auto valve in the fuel return line.

Or you could just be a cheap SOB like me and tystrap a couple pieces of cardboard over the cooler when it turns cold weather. :lol:

retmil46 · **Posted:** Mon Jan 14, 2008 1:16 am

MrMopar64 wrote:

The fuel temp sensor is used to form the protection strategy for the high pressure pump - as the fuel temp crosses a certain threshold, it will begin to limit the fuel flow through the pump/rail/in-cylinder injection and thusly engine torque so that the fuel temps will begin to drop.

Exactly. And THAT'S why I installed a cooler in the fuel return line for hot weather ops.

Just ducky. Not only did they want to detune the engine to make thier torque converter hold together, it was already programmed to detune itself to keep the fuel tank from getting too warm.

With apologies to Reflex, I guess it was cheaper to pay the software engineers to write in a few lines of code to do this, than to install a cooler, thermostat, and selector valve.

Reflex · **Joined:** Mon Jan 29, 2007 8:48 pm **Posts:** 567

retmil46 wrote:

With apologies to Reflex, I guess it was cheaper to pay the software engineers to write in a few lines of code to do this, than to install a cooler, thermostat, and selector valve.

How much you want the diesel option to cost? There's no such thing as the company eating the difference, and US auto manufacturers profit around $500/vehicle as it stands(by comparison, the average profit on a Japanese one is $2000/vehicle). That means that every piece you add adds cost, and not just the cost of the piece, but cost of testing, manufacturing, design, warranty and parts stocking, training, etc etc. Even a minor part could add far more than its cost to the end price of the product.

Since the vehicle functions just fine in this design, it sounds to me like they made the right decision. Especially in light of how everyone seems to complain about the price of a Grand Cherokee, which has a somewhat higher end diesel option(and a price to match).

Everyone has their personal opinon of how any given product 'should' be designed. But the problem is that there are as many opinions as there are users of a product, and the manufacturer could nto please them all without making the price out of range for everyone(even provided they could find ways to resolve the contradictory design requests).

retmil46 · **Posted:** Mon Jan 14, 2008 12:57 pm

Reflex wrote:

retmil46 wrote:

With apologies to Reflex, I guess it was cheaper to pay the software engineers to write in a few lines of code to do this, than to install a cooler, thermostat, and selector valve.

How much you want the diesel option to cost? There's no such thing as the company eating the difference, and US auto manufacturers profit around $500/vehicle as it stands(by comparison, the average profit on a Japanese one is $2000/vehicle). That means that every piece you add adds cost, and not just the cost of the piece, but cost of testing, manufacturing, design, warranty and parts stocking, training, etc etc. Even a minor part could add far more than its cost to the end price of the product.

Since the vehicle functions just fine in this design, it sounds to me like they made the right decision. Especially in light of how everyone seems to complain about the price of a Grand Cherokee, which has a somewhat higher end diesel option(and a price to match).

Everyone has their personal opinon of how any given product 'should' be designed. But the problem is that there are as many opinions as there are users of a product, and the manufacturer could nto please them all without making the price out of range for everyone(even provided they could find ways to resolve the contradictory design requests).

Only slightly misunderstood. Wasn't so much a complaint as it was a grudging acknowledgement of the reality we have to deal with, and didn't want you to think I was taking a cheap shot at your chosen profession.

retmil46 · **Posted:** Mon Jan 14, 2008 2:17 pm

In the Feb issue of Diesel Power, there's an article on Ford's new diesel 6.4 L. Looks like they've given up on HEUI and went with high pressure common rail and piezo injectors. A few things I found interesting -

A horizontal fuel conditioning module (HFCM) under the bed sends fuel thru a 10 micron water sep filter, and also has a diesel thermo recirculation (DTRC) valve which decides whether to port cold fuel from the tank or hot return fuel back to the engine.

A 4 micron final filter at the engine prior to getting to the injection pump.

A liquid cooled fuel cooler mounted on the turbo crossover pipe.

EGR is sent back to the engine after going thru an oxidation catalyst and TWO EGR coolers, temp reduction of gases upwards of 980 F. That sucker must have one heck of a radiator on it.

Let's see, that makes Powerstroke, Duramax, VW TDI, and every OTR rig we roll off the line for Oz and New Zealand that gets a fuel cooler that I know of.

Reflex · **Joined:** Mon Jan 29, 2007 8:48 pm **Posts:** 567

retmil46 wrote:

Only slightly misunderstood. Wasn't so much a complaint as it was a grudging acknowledgement of the reality we have to deal with, and didn't want you to think I was taking a cheap shot at your chosen profession.

Understood, I wasn't upset, just saying that everything has costs beyond just the part. When I go to meetings and someone proposes even a tiny change to a design spec seeing the program managers calculate the costs and come up with seemingly ridiculous figures is always mind boggling. And with how many of them are not even development related, like legal and assurances for requirements in other countries, etc. Its honestly quite frustrating, there is no room for a designer to truly be creative, IMO.

DarbyWalters · **Posted:** Mon Jan 14, 2008 2:39 pm

The problem with all this talk about testeing costs ect. does not change the fact that it does not work a lot of the time. Sometimes they make changes without proper testing...sometimes they let a bad thing roll out and make the consumer live with it. Example...Lower Ball Joints:They have never addressed the issue with a fix. How do I know? I had a 2002 Jeep Liberty with the LBJ Recall...every year since the recall has been in effect for all year models. I purchased a 2006 CRD and guess what...the LBJ Recall is needed. It doesn't take "testing" to see there is a problem and that is the same way many shortcomings are handled. It has nothing to do with Testing Costs...the tests were free and supplied by the consumer...it has to do with not caring about putting out a well designed safe product enough to fix the problems correctly. Honestly, if the KJ CRD had cost another $1000.00 but had the correct fixes of known discovered problems...I would have gladly paid it. About a 4% increase to get a much better quality vehicle?...not out of line IMHO.

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