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Poor fuel mileage, temps too low?
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Author:  palouse [ Sat Dec 07, 2013 4:16 pm ]
Post subject:  Poor fuel mileage, temps too low?
18 pulling 1500lb trailer, 19 mostly interstate commute.

Temp gauge never reads above second line. (C=1, middle=3, H=5).

Stuffed cardboard I front of fan, 66% coverage, for current 2000 mile trip. Temps raised to one notch above second large line. Still long way from middle or '12:00'.

Many posts about low temp causing comPuter to feed too much fuel. No definite info found.

Urban legend? If not, what thermostat do I need to install to get temp to 12:00?

2006 CRD. I've changed everything recommended in noob guide.

(iPhones suck!!!)
Author:  MRausch82 [ Sat Dec 07, 2013 4:18 pm ]
Post subject:  Re: Poor fuel mileage, temps too low?
Sounds like a stuck open thermostat. Common issue. Replace it and that will help. The MPG in the winter/cold does decrease.
Author:  racertracer [ Sat Dec 07, 2013 6:21 pm ]
Post subject:  Re: Poor fuel mileage, temps too low?
palouse wrote:
18 pulling 1500lb trailer, 19 mostly interstate commute.

Temp gauge never reads above second line. (C=1, middle=3, H=5).

Stuffed cardboard I front of fan, 66% coverage, for current 2000 mile trip. Temps raised to one notch above second large line. Still long way from middle or '12:00'.

Many posts about low temp causing comPuter to feed too much fuel. No definite info found.

Urban legend? If not, what thermostat do I need to install to get temp to 12:00?

2006 CRD. I've changed everything recommended in noob guide.

(iPhones suck!!!)


1. What tires are you running?

2. Mileage on the vehicle?

3. When was the last time the rear differential was cleaned out and filled with new gear oil?

4. When was the last time the front differential oil was drained and filled with new gear oil?

5. When was the last time the transmission fluid and filters were changed?

6. When was the last time the Transfer case oil was changed?

7. When was the last time the motor oil and filter was changed?

8. When was the last time the Air filter was changed?

9. When was the last time the Fuel filter was changed?

10. If you don't have a GDE tune then unplug your MAF sensor.

If you have high miles on your vehicle and your fluids haven't been changed on schedule and are due, then I would start there.

And while you're at it, don't forget to flush and fill the cooling system.

You should see about a 2MPG gain just by changing the oils.

Regarding the Thermostat, experts will be chiming in soon on that. My preference is the OEM unit, although some have used the inline Stant #13519 thermostat with good results. There is a thread on that subject.

P.S. What's the matter with the IPHONE.
Author:  palouse [ Mon Dec 09, 2013 4:29 pm ]
Post subject:  Re: Poor fuel mileage, temps too low?
racertracer wrote:

1. What tires are you running?
2. Mileage on the vehicle?
3. When was the last time the rear differential was cleaned out and filled with new gear oil?
4. When was the last time the front differential oil was drained and filled with new gear oil?
5. When was the last time the transmission fluid and filters were changed?
6. When was the last time the Transfer case oil was changed?
7. When was the last time the motor oil and filter was changed?
8. When was the last time the Air filter was changed?
9. When was the last time the Fuel filter was changed?
10. If you don't have a GDE tune then unplug your MAF sensor.

Regarding the Thermostat,
P.S. What's the matter with the IPHONE.

I went to Decature, AL, to buy the CRD from a lot, late August. Dealer wasn't even done "inprocessing" the vehicle. It had nearly bald P225/76r16 Firestone tires. The Chevy service center where dealership sent vehicle for basic maintenance used Delco 15w40 for "fresh oil change". (I spoke to the Chevy guys by phone.)

Return trip from AL, 650 miles, 25+ mpg, adjusted for incorrect pinion factor. Thus, I know the rig can get me closer to fuel mpg that I want.

Since the initial trip mpg check, I have made ~20 mpg in September; 13.8, worst case.
Since Friday, 2050 mile trip, 4 to -21 temps pulling trailer, best was 17.5, and one fill up on pure "Diesel #1" was 15 mpg (lost 1 mpg over equivalent flat terrain and #2). Some large diesel retailers are selling diesel #2 and #1 in side by side pumps for "blend-your-own" delivery to tank. For the trip, running #2 if possible, (and attendant seems confident that it is #2.) I am using "white bottle" PowerService supplement, as per directions. Recalls completed. GDE says this Jeep not on their list of installs.

1) New LT225/75r16 Michelin LTX MS (not MS\2). 80 psi. Old lit says "low rolling resistance" tire.
2) Today, 57k; Purchased 51k. 2 PO's, one towed it behind RV.
3-6) Don't know date of last changes. At proper levels. Didn't plan to change filter for tran, but will have fluids changed to complete 50 K maint, soon.
7, 8, 9) Thanksgiving.
10) MAF unplugged since Thanksgiving. The MAP sensor was relatively clean; it is clean now. With CEL light gone, and clean MAP, makes me think PO ran without MAF connected.

Only temp indicator (low), glow plug error code, no cruise control, pinion factor, finishing 50K maintenance, and, now, left trailer turn signal are current issues. Took it to dealer for pinion factor change, I told them to set it to tire manufacturer "rotations per mile", they said "yes", and after service told me "oh, we don't do it that way, we use the interal matrix". Pinion factor is still wrong, and I wasted 4 hours.

iPhone is made for people who stop to use hand cream every 45 minutes during the day, while in the office. My fingers have seen too many winters moving ice sheets around the pond to make room for the decoys, ("waterproof gloves" is an oxymoron.) I was trying to type for help on the mileage questions, in a McD's parking lot, after adusting the tarp on the trailer in 4 degree, 15 mph breeze. I need a tactile button arrangement, but appreciate that the boss pays for the phone bill and phone.
Author:  racertracer [ Mon Dec 09, 2013 8:27 pm ]
Post subject:  Re: Poor fuel mileage, temps too low?
palouse wrote:
racertracer wrote:

1. What tires are you running?
2. Mileage on the vehicle?
3. When was the last time the rear differential was cleaned out and filled with new gear oil?
4. When was the last time the front differential oil was drained and filled with new gear oil?
5. When was the last time the transmission fluid and filters were changed?
6. When was the last time the Transfer case oil was changed?
7. When was the last time the motor oil and filter was changed?
8. When was the last time the Air filter was changed?
9. When was the last time the Fuel filter was changed?
10. If you don't have a GDE tune then unplug your MAF sensor.

Regarding the Thermostat,
P.S. What's the matter with the IPHONE.

I went to Decature, AL, to buy the CRD from a lot, late August. Dealer wasn't even done "inprocessing" the vehicle. It had nearly bald P225/76r16 Firestone tires. The Chevy service center where dealership sent vehicle for basic maintenance used Delco 15w40 for "fresh oil change". (I spoke to the Chevy guys by phone.)

Return trip from AL, 650 miles, 25+ mpg, adjusted for incorrect pinion factor. Thus, I know the rig can get me closer to fuel mpg that I want.

Since the initial trip mpg check, I have made ~20 mpg in September; 13.8, worst case.
Since Friday, 2050 mile trip, 4 to -21 temps pulling trailer, best was 17.5, and one fill up on pure "Diesel #1" was 15 mpg (lost 1 mpg over equivalent flat terrain and #2). Some large diesel retailers are selling diesel #2 and #1 in side by side pumps for "blend-your-own" delivery to tank. For the trip, running #2 if possible, (and attendant seems confident that it is #2.) I am using "white bottle" PowerService supplement, as per directions. Recalls completed. GDE says this Jeep not on their list of installs.

1) New LT225/75r16 Michelin LTX MS (not MS\2). 80 psi. Old lit says "low rolling resistance" tire.
2) Today, 57k; Purchased 51k. 2 PO's, one towed it behind RV.
3-6) Don't know date of last changes. At proper levels. Didn't plan to change filter for tran, but will have fluids changed to complete 50 K maint, soon.
7, 8, 9) Thanksgiving.
10) MAF unplugged since Thanksgiving. The MAP sensor was relatively clean; it is clean now. With CEL light gone, and clean MAP, makes me think PO ran without MAF connected.

Only temp indicator (low), glow plug error code, no cruise control, pinion factor, finishing 50K maintenance, and, now, left trailer turn signal are current issues. Took it to dealer for pinion factor change, I told them to set it to tire manufacturer "rotations per mile", they said "yes", and after service told me "oh, we don't do it that way, we use the interal matrix". Pinion factor is still wrong, and I wasted 4 hours.

iPhone is made for people who stop to use hand cream every 45 minutes during the day, while in the office. My fingers have seen too many winters moving ice sheets around the pond to make room for the decoys, ("waterproof gloves" is an oxymoron.) I was trying to type for help on the mileage questions, in a McD's parking lot, after adusting the tarp on the trailer in 4 degree, 15 mph breeze. I need a tactile button arrangement, but appreciate that the boss pays for the phone bill and phone.


:lol:



Ok then.... keep up the good work and for sure you're on your way to better mileage. New gear oil makes for better mileage too.
Author:  palouse [ Sat Mar 29, 2014 8:45 pm ]
Post subject:  Re: Poor fuel mileage, temps too low?
Update since Dec 9, for those with thermostat issues. While visiting relatives, I got tired of 18-19 MPG. I "fixed" the termostat with a 5 gallon wood paint stir stick and a 33 gallon black plastic trash bag. I stopped in a parking lot free of snow, laid down in front of the Liberty, and with stir-stick from underneath, I stuffed the trashbag between the two radiators. I made sure that bag was evenly spread out. I found a slot on the top side of the radiators from the engine compartment that would allow a small (1 gallon) paint stir stick to be used for controlling height the bag reached between the radiators. (Stuff it back the other way.) I experimented with the amount of coverage, with "full" best performer, and no over-heat issues (that I noticed.) Between ~Dec 13 and last week, the Jeep was in above-freezing weather maybe 4 or 5 afternoons.

Cruising temp rose to "just left of top-center" on the dash thermometer. Bag has been there since Dec. While in California, mileage rose to 25 MPG. Milage has been in the 20-22 range, pushing 23 on one recent 250 mile trip.

I will get the thermostat replaced, along with glow plugs, soon.
Author:  papaindigo [ Sun Mar 30, 2014 6:58 am ]
Post subject:  Re: Poor fuel mileage, temps too low?
If not at or near 100K miles do timing belt ASAP based on age alone. Bad tstat (failed open and engine not reaching full operating temp) costs 10% mpg based on personal experience in N. FL winter, would be worse in colder climates.
Author:  woodtick [ Sun Mar 30, 2014 10:33 am ]
Post subject:  Re: Poor fuel mileage, temps too low?
You also mentioned a 1500# trailer. You also mentioned Ducks hunting. If this trailer is hauling a boat, put a tight fitting cover on the boat for less wind resistance. I tow an 18' Lund with full windshield and a 150Merc with the cover on highway runs and turn 18-20 mpg with this rig in tow.

Other item may be things like a brake dragging. I recently cured this and gained 2 mpg city. There are a number of causes for this issue. Flexible brake line internal deterioration, bad caliper, or in my case, the PO did not "fit" the pads and they bound. The cure for this is preventative action at install. The metal stamping of the brake pad has "fingers" that ride in a grove. I have been finding that I need to file to get no resistance as the stamping tolerances suck. A slight amount of slop is IMHO optimal.


Also watch the tach. anything over 2k rpm mileage falls off quick.
Author:  thermorex [ Sun Mar 30, 2014 10:37 pm ]
Post subject:  Re: Poor fuel mileage, temps too low?
woodtick wrote:
... the PO did not "fit" the pads and they bound. The cure for this is preventative action at install. The metal stamping of the brake pad has "fingers" that ride in a grove. I have been finding that I need to file to get no resistance as the stamping tolerances suck. A slight amount of slop is IMHO optimal.


This is a very, very objective and to the point observation. Many pads fit too snug in the caliper, some light grinding is a must. There is also a ceramic grease (Napa sells it) that is very good for brakes, where the pins and pads slide. The rubber bushings that go over the guiding pins can swollen up and also be a cause for brake drag. I removed mine. Windy weather can drop the mileage easy for up to 5 mpg.
Author:  woodtick [ Wed Apr 09, 2014 8:34 pm ]
Post subject:  Re: Poor fuel mileage, temps too low?
palouse wrote:

I will get the thermostat replaced, along with glow plugs, soon.


Well, have you made any of the suggested changes (aside from the plastic bag/ stick trick) to improve MPG?
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