Thermostat temperature specification: Fuel Mileage

altdiesel · **Posted:** Mon Jul 23, 2012 5:14 pm

I thought my thermostat was sticking, as it would only get to about 172 degrees at full operating temp without the a/c running. I replaced the thermostat, and still am reading temperatures around 172. I am reading the temperatures through the OBDII port, by the way, and the dash temp gauge reads a slight tick to the left of center. Since I have had my Jeep, I have averaged about 21 MPG, all hand calculated. I replaced the turbo hoses with SAMCO's, in tank fuel pump, new fuel heater head, Torque converter, and Transmission pump. I just returned from a long road trip doing about 4,000 miles, driving about 70 MPH, with A/C, and still only averaged about 21.4 MPG. Oh, and I have the full torque GDE tune.

Anyone have any ideas? If I don't start getting the fuel mileage I want, I am going to trade it in for either a different Jeep, or an Excursion.

naturist · **Posted:** Mon Jul 23, 2012 5:45 pm

That is really odd. The dashboard gauge seems to be where IT is supposed to be, but the temp you are getting is definitely low, suggesting either that reading is wrong, or there's real weirdness happening.

altdiesel · **Posted:** Mon Jul 23, 2012 6:47 pm

naturist wrote:

That is really odd. The dashboard gauge seems to be where IT is supposed to be, but the temp you are getting is definitely low, suggesting either that reading is wrong, or there's real weirdness happening.

Oh, I am sure there is real weirdness happening, and it is driving me crazy!

fish1 · **Posted:** Mon Jul 23, 2012 7:04 pm

Im having the same mpg problem ! Recently got GDE full torque eco tune i only average 21/22 mpg , but i do not know what my coolent temp is my gauge stays about 1 click left of center ! Been hoping it's gonna get better soon i just got samcos last week. One of the deciding factors when it came to buying the CRD was 24/25 avg. mpg and maybe into the low 30rd"s with a tune on the highway from the research i did before buying. I still like my CRD and i don't think i will be getting rid of it. Might call GDE see if they can help me out.

joelukex4 · **Joined:** Thu Sep 29, 2011 4:54 pm **Posts:** 386

What type of fuel mileage did you get before the ecotune? Did your mileage actually go down?

crawdad-480 · **Joined:** Fri Jan 19, 2007 12:03 pm **Posts:** 47

I have a 06 CRD that I had the same problem with for about a year. No matter what I seemed to try I could not get my
jeep to break 23 mpg. I did not matter how much interstate I drove, it just would not go past 23 mpg. My temp gage was
always just to the left of center and showed about 173 F through the OBD port. After much nashing of teeth and killing
of brain cells, I now have my mileage consistently above 25 mpg. I not sure how I fixed it but the last 6 tanks have been
about 25-27 mpg and the next tank is looking to be about 27 mpg. So here are the mods and what I have done:

1. GDE Eco tune (w/full torque)
2. GDE TCM tune (had keith remove the clutch lock up from 3rd gear. The whinning engine noise at about 45 mph was getting annoying.)
3. ProVent 200.
4. Suncoast torque converter (version 1)
5. In tank lift pump

Here is what I did right before the mileage went up.

1. Replaced air filter
2. Changed oil (I switched from Rotella to mobile one. I kept the weight the same, 5W-40.)
3. Removed the EGR valve to make sure it was not partially stuck open.
4. Added a in-line thermostat to raise the operating temp to 190 F.
5. Emissions test (required for registration) During the test there was enough white smoke to make a
fog bank for a horror movie, but everything passed. Maybe it just helped clear
something out. Also, I do keep an eye on the oil level and it does not use up oil.

I am not sure what one thing or maybe a combination of things helped to get my mileage back up. The last 6 tanks have resulted in
27.1, 25.5, 26.9, 27.2, 25.2 & 27.4 mpg. Results are hand calculated. Do shop around for diesel fuel. The quality of the fuel
can have an impact on your mpg. I have noticed as much as 2 mpg between different stations.

Don't give up to fast on the jeep, I fought with mine for 5 years to undo the crap chrysler did. Now that I've got the jeep running good
and the mileage back up. I'm happy with it.

Hope this helps.

altdiesel · **Posted:** Tue Jul 24, 2012 1:55 am

joelukex4 wrote:

What type of fuel mileage did you get before the ecotune? Did your mileage actually go down?

Before I got the full torque tune, I was getting in the 20's. 20.9 etc... After the tune, and with 6 tanks of fuel, I am averaging about 21.6, 22 on the highway, driving 75 MPH, with A/C on full blast. With this style of driving, I am still getting about 189 degree/ a/c off, about 172 degrees.

I really don't want to give up on the jeep, and I have another 30,000 miles left on the extended warranty I bought, so if there is something major that needs to be looked at/ replaced nearing 86,000 miles, please chime in!

bugnout · **Posted:** Tue Jul 24, 2012 5:27 pm

One thing I can recommend is slow down.

The CRD gets the best fuel mileage around 1800-2000 RPM. For me thats around 65 mph, and results in 2-4 mpg better fuel economy.

WolverineFW · **Posted:** Tue Jul 24, 2012 7:12 pm

bugnout wrote:

One thing I can recommend is slow down.

The CRD gets the best fuel mileage around 1800-2000 RPM. For me thats around 65 mph, and results in 2-4 mpg better fuel economy.

Agreed. My mileage is much higher in this range. Laws of physics still apply no matter what drivetrain mods you make.

ATXKJ · **Posted:** Tue Jul 24, 2012 8:59 pm

bugnout has 235/85/16 and 4:10 diff's - his rpm range will reflect that.

GDE has mentioned the most efficient temp range should be ~190F - the stock thermostat won't get there
the tick one mark left of center - is a 40F tick - from 170 to 210 - no motion - the needle just stays there.

I'm trying the Stant - in hose thermostat - it's locked on 191 (Scangauge) for casual driving
I would not use it if climbing hills or towing - I think you'll overheat too fast (I saw a 203 on a warmer day - considering the drive that was too much)

altdiesel · **Posted:** Wed Jul 25, 2012 1:31 am

WolverineFW wrote:

bugnout wrote:

One thing I can recommend is slow down.

The CRD gets the best fuel mileage around 1800-2000 RPM. For me thats around 65 mph, and results in 2-4 mpg better fuel economy.

Agreed. My mileage is much higher in this range. Laws of physics still apply no matter what drivetrain mods you make.

I am not trying to get out of the ball park fuel mileage, just what I think I should get as stock. As stock, I was hoping to get 22 city, 28 highway. Is this not what is normal? The reason I bought the Liberty was to get this kind of fuel mileage, as I do a lot of highway driving.

TJ2 · **Posted:** Wed Jul 25, 2012 2:30 am

ATXKJ wrote:

bugnout has 235/85/16 and 4:10 diff's - his rpm range will reflect that.

GDE has mentioned the most efficient temp range should be ~190F - the stock thermostat won't get there
the tick one mark left of center - is a 40F tick - from 170 to 210 - no motion - the needle just stays there.

I'm trying the Stant - in hose thermostat - it's locked on 191 (Scangauge) for casual driving
I would not use it if climbing hills or towing - I think you'll overheat too fast (I saw a 203 on a warmer day - considering the drive that was too much)

Interesting. I bought a Stant back when it was being discussed as a replacement option to OE. Haven't put it in yet, but will do so in the fall. 100k maintenance will be due then anyway.

Is the dash temp gauge still a tick left of center when the scangauge reads 203?

papaindigo · **Posted:** Wed Jul 25, 2012 8:17 am

Just a reminder that the dash temp gauge gets its reading from a sending unit screwed into the back of the top of the tstat housing and I suspect the scan units look at the same data. Hence if the sending unit is sending bogus signals (ex. claiming high when coolant cold) both the dash gauge and the scan unit would report proper operating temps but your mpg would suffer. IMHO the only way to be positive of your coolant temp is an independent check which can be done with an inexpensive UV temp gun reading on the tstat housing.

Geordi and racer posted some UV gun readings a while back at viewtopic.php?f=5&t=62047&p=725695&hilit=geordi+temp*#p725695 when racer was dealing with coolant leak problems before a rug totaled his ride.

Thermostat temperature specification: Fuel Mileage

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