Poor fuel mileage

chillmobil · **Joined:** Sun Jul 10, 2011 5:46 pm **Posts:** 34

Hi everyone,

So I've had my lovely CRD for 2 months now. It has been an interesting ride so far. Within 2 weeks the Boost hoses and alternator blew but since then it runs like a charm except for the real rattle up front when I am in reverse gear with my foot on the brake.

But what I have been noticing is a real decline in my fuel efficiency and I have no idea why. My first trip from Calgary to Kelowna BC (560 km) I averaged 29.7 mpg. Since then I have cleaned my sooty MAP, changed to new tires, changed my boost hoses and have experimented significantly with Off Road Modification (connecting and disconnecting the MAF sensor) and it just seems like my efficiency is going down all the time. As I posted earlier, I am not seeing much of a difference with MAF on or off.

I am getting 18 mpg best case in town driving but my last tank I had about 20% in town driving and 80% nice smooth and steady highway and I only still had about 20.5 mpg. This last tank I drove to Vancouver, on cruise control, even shifting to Neutral down big steep hills to coast as much as I could and still only 22 mpg. Seems like I am 20% lower than what I should be. Any thoughts? I don't think I could be driving much slower and smoother!

Thanks for any insight.. I want the GDE eco tune for sure but would like to get my CRD up to normal efficiency range before I drop the $500.

irollgen4s · **Posted:** Mon Oct 17, 2011 3:41 pm

what does your thermostat look like when you've been driving on the highway for say 5~ miles? if its anything lower then 1 click to the elft of straight up, your thermostat is going bad and will not let the motor heat up properly.

papaindigo · **Posted:** Mon Oct 17, 2011 5:11 pm

Thoughts:
Basic mpg no modifications based on in town 10 mile runs from cold start max speed 45mph average more like 20mph the mpg should be on the order of 19mpg. Hwy running 62 mph w/without AC windows up, 1800rpm in full lockup (if F-37 this means run upto 63-64 until full lockup and drop back to 62mph/1800rpm) the mpg should be 28-29mpg. Post GDE EcoTune same driving the figures are more like 22/32mpg.
Issues to consider: 1) my bet on your rattle is a failed engine mount but that should not impact mpg; 2) you changed tires-even if you stayed with the same nominal tire size the actual tire size can be significantly different which will impact apparent mpg which leads to #3; 3) have you calculated mpg based on GPS miles traveled or are you relying on the notoriously inaccurate EVIC; 4) are you filling the tank to the same level (ideal way to get accurate check is to carefully fill until you see fuel in the filler neck; drive; refill to same level and calculate); 5) is the fuel filter new or old and clogged; 6) have you checked for a dragging brake (easy way, drive 10 miles and see if 1 or more wheel(s) are blazing hot); 6) check for all around proper tire pressure; 7) are you buying fuel from a name brand dispenser that sells lots or at the cheapest place you can find;

are your injectors clean (run a can of diesel injector cleaner - that alone can add 2+mpg)
Others may have more thoughts to add.

chillmobil · **Joined:** Sun Jul 10, 2011 5:46 pm **Posts:** 34

irollgen4s wrote:

what does your thermostat look like when you've been driving on the highway for say 5~ miles? if its anything lower then 1 click to the elft of straight up, your thermostat is going bad and will not let the motor heat up properly.

Interesting, I am definitely not running straight up. I think with MAF connected, I am one or 2 clicks left of straight up and with it disconnected, I am slightly above the quarter mark from the left. Perhaps I should look into this.. Thanks for the insight.

Sir Sam · **Posted:** Tue Oct 18, 2011 12:20 pm

chillmobil wrote:

irollgen4s wrote:

what does your thermostat look like when you've been driving on the highway for say 5~ miles? if its anything lower then 1 click to the elft of straight up, your thermostat is going bad and will not let the motor heat up properly.

Interesting, I am definitely not running straight up. I think with MAF connected, I am one or 2 clicks left of straight up and with it disconnected, I am slightly above the quarter mark from the left. Perhaps I should look into this.. Thanks for the insight.

yup, sounds like you need a new thermostat.

chillmobil · **Joined:** Sun Jul 10, 2011 5:46 pm **Posts:** 34

papaindigo wrote:

Thoughts:
Basic mpg no modifications based on in town 10 mile runs from cold start max speed 45mph average more like 20mph the mpg should be on the order of 19mpg. Hwy running 62 mph w/without AC windows up, 1800rpm in full lockup (if F-37 this means run upto 63-64 until full lockup and drop back to 62mph/1800rpm) the mpg should be 28-29mpg. Post GDE EcoTune same driving the figures are more like 22/32mpg.
Issues to consider: 1) my bet on your rattle is a failed engine mount but that should not impact mpg; 2) you changed tires-even if you stayed with the same nominal tire size the actual tire size can be significantly different which will impact apparent mpg which leads to #3; 3) have you calculated mpg based on GPS miles traveled or are you relying on the notoriously inaccurate EVIC; 4) are you filling the tank to the same level (ideal way to get accurate check is to carefully fill until you see fuel in the filler neck; drive; refill to same level and calculate); 5) is the fuel filter new or old and clogged; 6) have you checked for a dragging brake (easy way, drive 10 miles and see if 1 or more wheel(s) are blazing hot); 6) check for all around proper tire pressure; 7) are you buying fuel from a name brand dispenser that sells lots or at the cheapest place you can find;

are your injectors clean (run a can of diesel injector cleaner - that alone can add 2+mpg)
Others may have more thoughts to add.

Thanks for the great insight. Good to know where I should be, gives me something to work towards. I did calculate my speed relative to my GPS and my speedometer shows me going 10% faster than I am actually going (across the speed range from 20-100 km/h). If the speedometer relates to my odometer, then my mileage is actually 10% worst!! I have never checked for dragging brake, will do. I always fill to the 2nd click of the gas filler handle. I don't have an EVIC so all my calcs are made from my nifty little iPhone app. I will definitely run a bottle of injector cleaner. Wondering if by trying to drive as smooth as possible, is that contributing to sooth build up in engine? Ie, is it good once in a while to floor it and leave a black cloud behind?
Thanks!

Sir Sam · **Posted:** Tue Oct 18, 2011 12:36 pm

chillmobil wrote:

papaindigo wrote:

Ie, is it good once in a while to floor it and leave a black cloud behind?
Thanks!

No, you should floor it regularly and never see a black cloud.

Radman · **Posted:** Tue Oct 18, 2011 12:59 pm

Winter diesel fuel will also impact your fuel economy. At this time of year most suppliers have or are switching over to witerized fuel.

papaindigo · **Posted:** Tue Oct 18, 2011 1:40 pm

As far as I know the accuracy of the speedometer and odometer are not related at least on the 3 CRDs I'v "touched" with a GPS the variations in accuracy of the 2 gauges does not correlate.

dirtmover · **Posted:** Tue Oct 18, 2011 2:05 pm

Agreed, my speedometer is ~10% high but my odometer is ~5% low.

Siardi · **Posted:** Tue Oct 18, 2011 6:02 pm

So is it possible to loose as much as 4MPG's just for running the engine cold?

I've been getting about 22 MPG's average, I don't see a lot of improvement when I do mostly Hwy opposed to sometimes being stocked in traffic, and noticed that since I bought the car about 2 month ago the thermostat stays (for the most part) just one tick over the quarter mark, and sometimes, very rarely I see it on the top (almost straight up) and not for long.

My MPG's have been from 19 MPG's on one tank to a best of 24,5 MPG's on a recent tank averaging 22. Always fill up at the same brand station, due to work I cannot use the same location, and use the second click on the thing... I hand calculate all my readings.

I've been putting off the inline thermostat due to work, but if I'm loosing so much money I'll make it a priority, I drive sometimes over 300 miles per day, those savings will add up quickly.

Thanks !!!

boilermaker2 · **Posted:** Tue Oct 18, 2011 7:44 pm

Switching to winter diesel AND losing the T-stat can lead to a 4mpg fuel loss. The winter diesel is worth about 2mpg (several variables here) and the T-stat is good for another 2mpg. If temps are dropping and have stayed low, you may also want to check your tire temp.

Lastly, this is a electric sucking beast until it is fully hot in cold climes. Think about the morning commute:
1.) cold start
2.) lights on (dark now)
3.) defrost if frosty (A/C in front and electric heat in rear)
4.) electric fuel heater
5.) viscous/friction/fuel-sucking heater for the humans in the cab
6.) glow plugs staying on until the computer is happy (long after your little light goes out)
In the winter, I recharge the battery if my driving stems from repeated short commutes.

Singularly, not a problem, collectively it is a mileage sucking weight around the Libby's neck. Here are few things to consider to help (but not fully cure the problem).
1.) Park it in the garage with the garage door DOWN (venting a little, this took some sever spousal training/coaxing)
2.) Plug in the block heater. Consider a timer, it likely on needs a couple of hours to do what it needs to do (garage dependent :SOMBRERO:

)
3.) Get the ECO Tune from GDE, they have limited some of costs incurred from 4,5,&6 (I think)
4.) Crack the window instead of using defroster. The Bi-level or panel setting do not turn on the A/C compressor but the floor and defrost modes do (even if the button is not pushed in)
5.) Monitor you fuel location and associated mileage, some are different and the difference may vary by season.

There are other hyper-miler suggestions and I'll let those folks chime but these are little tips I use. Get the T-stat fixed, if you're close to 100,000miles, you may as well do the timing belt.

Good luck and welcome aboard,
Boilermaker2

boilermaker2 · **Posted:** Tue Oct 18, 2011 7:51 pm

Siardi wrote:

So is it possible to loose as much as 4MPG's just for running the engine cold?

I've been getting about 22 MPG's average, I don't see a lot of improvement when I do mostly Hwy opposed to sometimes being stocked in traffic, and noticed that since I bought the car about 2 month ago the thermostat stays (for the most part) just one tick over the quarter mark, and sometimes, very rarely I see it on the top (almost straight up) and not for long.

My MPG's have been from 19 MPG's on one tank to a best of 24,5 MPG's on a recent tank averaging 22. Always fill up at the same brand station, due to work I cannot use the same location, and use the second click on the thing... I hand calculate all my readings.

I've been putting off the inline thermostat due to work, but if I'm loosing so much money I'll make it a priority, I drive sometimes over 300 miles per day, those savings will add up quickly.

Thanks !!!

If you're getting 22mpg with 90%+ highway miles (starting/stopping this beast suck fuel), I'd guess you're driving 75 mpg without a GDE tune. Drop that to 70 with a GDE tune and good t-stat and it should be closer to 26. Drop it to 65 and you'll see 28. Drop it further to 62 and you'll likely play with 30. I draw the line at 65-67. My butt does not grow roots well in these seats. 62 mph on the highway for 5 hours is too long too consider one's afterlife...
:5SHOTS:

Boilermaker2

Siardi · **Posted:** Tue Oct 18, 2011 8:12 pm

Thanks for your reply!!

I probable drive 40% Hwy at 65MPH might be faster sometimes but not over 2000 RPM which is right at 68MPH, another 40% on back roads where the speed limit is 45/55 so not always on 5the gear (I don't have the T or P 37 (whatever that is) as mine engages the 5th gear at 57MPH) and another 20% on stop and go and < 20MPH. All of this with the AC always on, here in the ATL is still hot enough to run the AC all day except for the very first drive in the morning.
I don't have any sort of tune and no mods. I'm thinking of a few though.... My tires are right at 36 PSI, it's a little bumpy ride but I don't mind.

Anf forgot to mention the most important part.... I have been runing about 20% biodiesel in the last three tanks, surprisingly I saw a very slight increase on those three tanks, but only time will tell as my driving can vary greatly from one day to the next. One day I might be in the city driving 100 miles in the entire day and the next I might be in the country driving 250 miles of back roads. That's why I look at the long term and don't pay attention to the extreme low or high MPG's.

Thank you!!

Radman · **Posted:** Wed Oct 19, 2011 9:55 am

4.) Crack the window instead of using defroster. The Bi-level or panel setting do not turn on the A/C compressor but the floor and defrost modes do (even if the button is not pushed in)

I believe there is a thread here somewhere on how to modify the panel to disable the A/C from turning on in defrost mode?? I recall seeing pictures of how to modify it but cannot find them... may have been on another Jeep site...

chillmobil · **Joined:** Sun Jul 10, 2011 5:46 pm **Posts:** 34

Thanks everyone! This forum is truly amazing, what a wealth of knowledge. I will look into the thermostat. I will update when it is changed..

DynoPax · **Posted:** Wed Oct 19, 2011 11:08 am

X2 on the winterized fuel. My MPG is decreasing gradually lately, as it have been doing every time at this period of the year. Colder morning and more use of electric items also...

papaindigo · **Posted:** Wed Oct 19, 2011 11:36 am

Regarding the switch to disable AC in defrost mod I'm pretty sure that was posted by kapalczynski . Run a search of this forum based on his name and you should be able to find it.

chillmobil · **Joined:** Sun Jul 10, 2011 5:46 pm **Posts:** 34

Quick question re: thermostat.

If I have the MAF disconnected, I am running at one bar above quarter on the temp gauge. Is that normal or should the tempguage also read about all the way up, even with MAF disconnected?

Thanks

boilermaker2 · **Posted:** Thu Oct 20, 2011 11:56 am

If it is a tick above the quart mark, your T-stat is dead. If it is one tick to the left of half it is OK. There is a large thread to search for that even has picks and associated temps marked.

B2

Poor fuel mileage

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