CRD Fuel Mileage Drop in Cold Weather

We have had our '05 CRD Liberty for a year now and have noticed a consistent, 4-5 MPG drop when ambient temps go below 42 deg F (from 24-26 down to 20-21 in mixed driving). This is after full warm-up, so this eliminates the usual cold weather effect of richer running until full operating temp is reached.

I'm about to remove the cold air duct from the air box to the right headlight bucket and block off part of the grill opening.

Anyone have any experience with this or tried anything?

Thanks,

DOC

DOC4444 said:

We have had our '05 CRD Liberty for a year now and have noticed a consistent, 4-5 MPG drop when ambient temps go below 42 deg F (from 24-26 down to 20-21 in mixed driving). This is after full warm-up, so this eliminates the usual cold weather effect of richer running until full operating temp is reached.

I'm about to remove the cold air duct from the air box to the right headlight bucket and block off part of the grill opening.

Anyone have any experience with or tried anything?

Thanks,

DOC

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Winter fuel is to blame,all engines,gas or diesel get worse MPG's in the winter.

CRD Fuel Mileage

Guess you missed it. Same tank of fuel, same everything except ambient temp. Mileage on a day when ambient is 42F or above is 24-26. When temps drop below that, say the next day, mileage drops to 20-21.

Thanks,

DOC

DOC4444 said:

Guess you missed it. Same tank of fuel, same everything except ambient temp. Mileage on a day when ambient is 42F or above is 24-26. When temps drop below that, say the next day, mileage drops to 20-21.

Thanks,

DOC

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Temp affects desiel fuel alot,your fuel may be border line gelling up and the reason for the drop in mpg's.Modern desiels per say don't "richen" or "lean-out" like at gas engine does.The CRD is a "Common Rail Desiel" engine and there is not control on flow rate except for RPM increase.Also the colder the temps the longer it takes for the engine oil to warm up which can cause more drag reducing MPG's.I wouldn't block cold air from getting into the filter box,colder air is more dense thus making more power,it's the winter fuel that reduces the MPG's to reduce emissions in the winter.

tjkj's got it here. Winter Blend + Colder Temps + Harder to start engine + a whole bunch of other factors = Lower mileage.

It'll go back up in the springtime.

Bring it back down to basic Chem - Colder air = denser air = more oxygen. To remain stoichiometric, you thus need more fuel to match the oxygen, right?

All vehicles get less MPG in the winter. As a tradeoff, you get more power.

Stoichiometric doesn't mean anything to a diesel motor.

Winter fuel is part of it. A big part of it is the viscous heater, which is belt driven and churns to heat your coolant and keep the engine up to temp. It activates below about 45ºF, so that's what you're seeing. It draws power and drops your fuel mileage. You can unplug its clutch (it looks like an AC compressor on the upper passenger side front of the engine) and get a grille blanket to keep the engine warm.

CRD Mileage Drop

CATCRD,

Thanks! Your response clearly fits the facts that the other folks don't seem to have grasped since we have consistently been seeing this effect over and over ON THE SAME TANK OF FUEL. So, clearly, it's NOT a function of winter diesel. (BTW, it's my understanding that diesel is NOT mixed with less dense methanol/ethanol in the winter as gasoline may be. It's hard to see how the little amount of anti-gel that is blended in could lower the amount of energy per gallon as happens with winter blended gasoline. I would expect about a 2 MPG decrease in mileage in cold weather due to having to run longer with a slightly rich mixture due to longer warm-up times each drive cycle, but not the 4-6 MPG we have been seeing.)

So, do you know where the 45 degree temp sensor for the viscous heater is located? It would seem to me that if it is in the engine compartment (or even in front of the radiator) that blocking off the grill opening the right amount should do the trick w/o having to disable the drive clutch.

Thanks Again!

DOC

i had a cummins and it got the bad mpg when it was cold but try letting you car get warmed up cold boost+cold motor=crack block

DOC4444 said:

CATCRD,

Thanks! Your response clearly fits the facts that the other folks don't seem to have grasped since we have consistently been seeing this effect over and over ON THE SAME TANK OF FUEL. So, clearly, it's NOT a function of winter diesel. (BTW, it's my understanding that diesel is NOT mixed with less dense methanol/ethanol in the winter as gasoline may be. It's hard to see how the little amount of anti-gel that is blended in could lower the amount of energy per gallon as happens with winter blended gasoline. I would expect about a 2 MPG decrease in mileage in cold weather due to having to run longer with a slightly rich mixture due to longer warm-up times each drive cycle, but not the 4-6 MPG we have been seeing.)

So, do you know where the 45 degree temp sensor for the viscous heater is located? It would seem to me that if it is in the engine compartment (or even in front of the radiator) that blocking off the grill opening the right amount should do the trick w/o having to disable the drive clutch.

Thanks Again!

DOC

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Sometimes it's not just anti-gel that's blended with the winter fuel, but kerosene, which has lower energy content per gallon. Ethanol/methanol should never be added to diesel fuel.

I'm not sure which sensor is the one the ECU uses to turn on the viscous heater. It may be the one in the grille or the intake air temp sensor at the side of the air filter box. Fooling one of these sensors may have unintended consequences on the way the ECU computes proper fueling/boost etc.

If you don't want it to come on, disable it directly by unplugging it or removing the relay that controls it in the power distribution box.

Lower CRD Mileage in cold weather

CATCRD,

I ordered one of the Fia grill "blankets" as you use. I gather you run with the "vents" in the fully "closed" position during the winter and disable the viscous heater. Correct, or??? Any problem with this other than possibly extending initial warmup a little? At what ambient do you open the "vents" and at what temp do you completely remove the blanket? Do you plug the viscous heater back in, in the spring (probably moot), or keep it permanently disabled throughout the year?

Thanks Again,

DOC

Poor CRD Fuel mileage in cold weather

Had a chance to discuss the "viscous heater" with our local Jeep diesel tech in Lincoln, RI. He believes that the purpose of this device is ONLY to generate additional cabin heat more rapidly and has NOTHING to do with the needs of the engine for additional heat in the cooling system in cold weather. He sees no problem with disabling it, other than it could set a code, but he felt since you would know what it is, that it should not be a problem.

An extra 4-6 MPG in the winter would really help!


I will post an update regarding my experience. (Still awaiting grill blanket.)

DOC

I have the relays removed for the viscous heat on both of my CRDs. On the one with the grille blanket it takes about 3 miles to get up to full temp without the viscous heat, and 2 miles with it. This is after having the block heater come on 3 hrs before I leave for work. No codes set either.

I open the grille vents at about 50F. It was 70 yesterday and I was running down the highway at 80mph with both vents open. No problems. I knew it would be in the 30s today, so I didn't take it all the way off.