Oddly low MPG

irollgen4s · **Posted:** Wed Feb 02, 2011 3:57 pm

Hey, i have 06 CRD limited franky lifted with 265-75-16 E load general grabbers under it. I Also have a jl audio stealthbox with an amp set up that i always have going, but not always full blast. Now I just hand calculated my gas mileage, and im getting about 14 miles per gallon.... WHAT THE HELL? I have pictures of my temp gauge, and from what i've read its still fine, it's two clicks off of 90 degree's(vertical). I know I shouldnt be getting anything amazing like 26 or 28, but i feel like i should at least be in the 20's. This is with mixed driving, half town, half long 55+mph roads. Also i use four wheel drive very little, i had it on for five minutes this morning to see if it was icy, and then i use it whenever i happen to get stuck in slush or on ice while parked. I always have the heat on 1, the lowest setting and usually have it on feet and windsheild or feet and face.

The mapping is factory as well as the TCM, and i have been neutered with the f37 flash and i have the old F37 torque converter.

Help please?

Edit: also this is in winter temperatures and it sits outside all night and gets used during the day a bit. Temps range from 8 degree's at night to 40 on a good day. I have a light foot also, but have played in the snow a little bit too. I also know that gas stations put in some blend into the tanks so that it doesnt freeze or gel and i know this hurts the mieleage a bit too.

dgeist · **Posted:** Wed Feb 02, 2011 4:06 pm

Your fuel economy in full-time 4WD should not really suffer, FYI. I've gotten as high as 30 mpg on highway trips hauling loads in FT4W. The front drive shafts and differential are always spinning anyway, so you're not doing much (except sacrificing safety) by having it off.

Your t-stat is reading a bit low, but as you said, it's cold out. I'd take a long drive at highway speeds (at least 10-20 minutes if you can) and then put a scanner on it. You should be able to get coolant temperature from the computer. and it should be up around 180F. Much lower and your t-stat is likely toast.

Is it the original? If so, it's probably gone anyway. They seem to last about 4-5 years MAX on the CRDs, just about the factory coolant change interval

Dan

irollgen4s · **Posted:** Wed Feb 02, 2011 4:10 pm

No matter how i drive i can't get my temp to rise at all, thats why i've been thinking its the Tstat. Any chance i can get a factory one? ideally i'd like to get one from the member making it on here, but the car is used too often to wait for one. Also how hard is the thermostat replacement?

Edit: Yeah its the original, Never had an issue with temperature until this year, but it was also garage kept until this year.

dgeist · **Posted:** Wed Feb 02, 2011 4:46 pm

irollgen4s wrote:

No matter how i drive i can't get my temp to rise at all, thats why i've been thinking its the Tstat. Any chance i can get a factory one? ideally i'd like to get one from the member making it on here, but the car is used too often to wait for one. Also how hard is the thermostat replacement?

Edit: Yeah its the original, Never had an issue with temperature until this year, but it was also garage kept until this year.

Mark has a pretty long waiting list on the modified thermostat assemblies. If you need it now, factory is about the only option. It'll run you around $100 for the part (from any of the various mopar parts sites. The installation is not complicated, but you probably need to drain the cooling system (which it sounds like is a good idea for you anyway) and it's probably a couple hours getting all the hoses detached, labeled, tucked out of the way, and drained so you can get the old assembly off and the new one installed/re-assemble/re-filled/purged. Don't forget the gasket for the replacement if you mail-order it. I don't think the factory unit comes with one normally.

It probably wouldn't hurt to get on Mark's waiting list now. You may need another in the future

Dan

irollgen4s · **Posted:** Wed Feb 02, 2011 5:02 pm

I'll have to talk to my dad about it im thinking this is the issue.. because well, im getting 14 miles to the gallon and its steadily decreasing, i was getting 18mpg a tank or two ago.

Im not sure if this is relevant, but this all started after me and my dad installed my system, we disconnected the battery to prevent any accidents, and that set the settings to factory. we figured okay it'll work its way back up, but it has only been steadily decreasing..

I'm sure me and my dad are gunna have a friend of ours do it in his shop, so i would need the replacement thermostat housing(i assume it comes with everything in it..?) the gasket and HOAT(no idea what this is) antifreeze.. right?

warp2diesel · **Posted:** Wed Feb 02, 2011 8:12 pm

My temp gauge was reading low and I replaced the thermostat.
Works now, heat works better too.

irollgen4s · **Posted:** Wed Feb 02, 2011 8:34 pm

What i cant seem to determine is if its due to it being a cold harsh winter here, or if its the tstat. Im guessing its the tstat because of the hard hit in gas mileage, but i cant be sure unless i wait until it gets warmer.

LibertyCRD · **Posted:** Wed Feb 02, 2011 8:38 pm

First of all your t-stat is clearly failed. Mine was showing the same reading, and now with my new t-stat it goes half-scale even in sub zero weather. So there's a $125 fix.

Second, your 265/75 load range "E" tires are VERY heavy which hurts economy and TALL which also hurts economy.

Having said that...you should be seeing a realistic 18 MPG in mixed driving with your setup. If you are only getting 14 you've obviously got big problems. I get 15 towing almost 7,000 lbs. so I know something is wrong.

Dumb question...but you ARE calculating your MPGs based on your tall tires making your odometer count too slowly, right? Have you checked your brakes? KJs have been notorious for sticky brake calipers causing MPG decreases.

irollgen4s · **Posted:** Wed Feb 02, 2011 9:06 pm

Checked the speedo with my iphone gps and with a regular GPS and they both read the same, with these tires the speed is finally dead on. As for the sticky brakes, i havent checked it but seeing as i've been driving around on nothing but ice and nothing has happened due to brakes, i would think that theyre okay. But now that i think about it when we were putting the spacers on, everything spun nice and freely without any sticking.

I know the tires are tall and heavy, but its exactly what i wanted :SOMBRERO:

. As for the tstat im 99 percent sure thats my issue since i can't get it to read any higher what so ever, i'll try to convince my dad that the tstat is the issue and see where it goes.

VMKJCRD · **Posted:** Wed Feb 02, 2011 9:24 pm

trust me its the cold weather we're having here in Long Island. During the summer my temp would be one tick under the middle on the temp gauge. Ever since the weather got cold my temps have been the same as yours and my mileage dropped from 28mpg to I don't even want to remember. If I were you I would wait till the weather gets warmer and see if the temps climb. If you want to see if there's really something wrong with the tstat you can take her to the highway and really get on her and see if the temperature rises.

It could just be cold weather and also the winter fuel blend.

just my :2cents:

warp2diesel · **Posted:** Wed Feb 02, 2011 10:42 pm

VMKJCRD wrote:

trust me its the cold weather we're having here in Long Island. During the summer my temp would be one tick under the middle on the temp gauge. Ever since the weather got cold my temps have been the same as yours and my mileage dropped from 28mpg to I don't even want to remember. If I were you I would wait till the weather gets warmer and see if the temps climb. If you want to see if there's really something wrong with the tstat you can take her to the highway and really get on her and see if the temperature rises.

It could just be cold weather and also the winter fuel blend.

just my :2cents:

Denial is not a Rive in Egypt. At -20F the needle will be at 11:00 o'clock if your thermostat is working.
Yours is bad.

CATCRD · **Posted:** Wed Feb 02, 2011 10:48 pm

warp2diesel wrote:

VMKJCRD wrote:

trust me its the cold weather we're having here in Long Island. During the summer my temp would be one tick under the middle on the temp gauge. Ever since the weather got cold my temps have been the same as yours and my mileage dropped from 28mpg to I don't even want to remember. If I were you I would wait till the weather gets warmer and see if the temps climb. If you want to see if there's really something wrong with the tstat you can take her to the highway and really get on her and see if the temperature rises.

It could just be cold weather and also the winter fuel blend.

just my :2cents:

Denial is not a Rive in Egypt. At -20F the needle will be at 11:00 o'clock if your thermostat is working.
Yours is bad.

And since it's bad your viscous heater is running non-stop to keep coolant temps up. That will kill your mpg along with the winter fuel and cold, thick lubricants.

VMKJCRD · **Posted:** Wed Feb 02, 2011 11:08 pm

That's strange warp but even last winter my temp was the same. Summer came along and the temps would spike to a tick under the middle sometimes right at 12 o'clock on the temp gauge with occasional 28mpg hand calced. Also took her on the expressway to give er an "Italian tuneup" and noticed the needle rising over what it normally is and with the cabin heat, some times I have to bring it down because it gets to hot for me.

Now my question is.
If the tstat is bad, will it stay at whats pictures above even in warmer weather or will it rise to 11 o'clock on the temp gauge?

Just trying to figure some things out now.

stoutdog · **Posted:** Wed Feb 02, 2011 11:13 pm

VMKJCRD wrote:

Now my question is.
If the tstat is bad, will it stay at whats pictures above even in warmer weather or will it rise to 11 o'clock on the temp gauge?

It may be fine in warmer weather; it will probably be fine in warmer weather if the AC is running. But the tstat is still bad if, even in relatively cold weather (I can't speak for -30*), it isn't sitting one tick left of center.

BlackLibertyCRD · **Posted:** Wed Feb 02, 2011 11:40 pm

irollgen4s wrote:

Checked the speedo with my iphone gps and with a regular GPS and they both read the same, with these tires the speed is finally dead on. As for the sticky brakes, i havent checked it but seeing as i've been driving around on nothing but ice and nothing has happened due to brakes, i would think that theyre okay. But now that i think about it when we were putting the spacers on, everything spun nice and freely without any sticking.

I know the tires are tall and heavy, but its exactly what i wanted :SOMBRERO:

. As for the tstat im 99 percent sure thats my issue since i can't get it to read any higher what so ever, i'll try to convince my dad that the tstat is the issue and see where it goes.

The calibration of the 06 speedometer and odometer is both off in opposite direction. On the 06 the speedometer runs fast and the odometer runs slow. Jeep didn't have a flash to make them both right so they just got them balanced in the middle with one to slow and the other fast which is about 5% of true reading. What happen is when you put larger tires on and brought the speedometer down to the true reading you also slowed the odometer down. Now you odometer is 10% slow so you would have to add 10% more miles to your calculation. That would add up to better mileage.

edit: If you don't believe me, run some mile markers with the trip odometer and you will be getting .9 instead of 1 mile.

irollgen4s · **Posted:** Thu Feb 03, 2011 12:06 am

14 mpg was with any doubt of the tires and speedometer being off, with the correction in... with the correction out i had 12mpg. absolutely ridiculous considering my dad was getting 26 mpg highway with the same car.

BlackLibertyCRD · **Posted:** Thu Feb 03, 2011 1:28 am

I give up. :dizzy:

irollgen4s · **Posted:** Thu Feb 03, 2011 7:21 am

Im not trying to disprove you in anyway, im just saying with or without the correction, my mileage is still extremely off for what how im driving. I think im going to wait until its slightly warmer and then look into the thermostat more, mainly because my dad doesnt want to bother with it now

Thanks everyone!

warp2diesel · **Posted:** Thu Feb 03, 2011 7:42 am

VMKJCRD wrote:

That's strange warp but even last winter my temp was the same. Summer came along and the temps would spike to a tick under the middle sometimes right at 12 o'clock on the temp gauge with occasional 28mpg hand calced. Also took her on the expressway to give er an "Italian tuneup" and noticed the needle rising over what it normally is and with the cabin heat, some times I have to bring it down because it gets to hot for me.

Now my question is.
If the tstat is bad, will it stay at whats pictures above even in warmer weather or will it rise to 11 o'clock on the temp gauge?

Just trying to figure some things out now.

The thermostat is actuated by a tube of wax with a plunger in it that moves the disk(s) to control the water flow. When the plunger sticks so it does not work properly or has coolant get inside the chamber (fraction of one drop) the engine tends to run cold. When the wax leaks out, the engine runs hot because the thermostat does not open. Needless to say the thermostat actuator does not care what the weather is and just because it worked before does not matter. It is not like bad eyesight that progresses over time, it is like getting shot on the battlefield (or Ghetto). When the thermostat is shot it is not getting over it.

papaindigo · **Posted:** Thu Feb 03, 2011 8:30 am

x2 stoutdog. North Florida experience has been gauge reads nearly fine (.5 tick left of 12 o'clock) as long as ambient temp is over 70 degrees especially if ac is on. As temp drops so does gauge position until at 20-30 degrees gauge hovers 2.5-3 ticks left of 12 o'clock and won't move above that. That said when the engine is running cold my mpg drop was minimal from ca. 22-23 to 20-21 with just the GDE ECO tune. For what it's worth there seem to be 2 failure modes for the tstat: 1) fail completely open in which case the engine would take forever to warm up and mpg would likely go way down or 2) what happened to me, fail by opening way to early (e.g. at a lower than design temp) in which case the engine warms up to a point that's somewhat dependent on ambient temp but the mpg doesn't take a big hit.

After replacement with a new OEM tstat full operating temp (right edge of needle almost touching 12 o'clock) is reached in about 4-5 miles depending on ambient. Right now ambient has ranged from +21 to +70.

Cannot speak to - environment although others note with a functional tstat normal temp is reached.

FYI - my gauge has been flashed to have the correct diesel temp readings, see GDE technical thread on that issue.

Oddly low MPG

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