Fuel economy is slowly going down...

usa591 · **Posted:** Tue Sep 30, 2014 8:08 pm

Hi Team,

So I'm noticing a slow decrease in fuel economy over most of 2014 and I'm curious what y'all think. Check my Fuelly stats and you can see. The 19.3 MPG you see in my signature is the result of the average being affected by earlier "good" mileage.

I changed my thermostat last December (it was stuck in open position) and now my temp reads "normal" -- a tick or two to the left of of center. I expected economy to go up, but I feel that it's done the opposite by a few mpg's.

I am running Geolander A/T's, but I'm starting to get in the 16's when I do the hand calc at the pump.

Now, commutes since April have only been about 3.5 miles into work and another 3.5 to get home. But it's on the freeway and I keep it between 60 and 65. By the time I've gone a mile my engine temp is at that center mark… Could my relatively short commute be the reason? I consider 90% of my miles to be "freeway".

I perused some of the old threads on this topic and things I have done:

• GDE Eco Tune
• Changed tranny fluids & coolant at 45K or so (77 or so on the beast right now)
• New air filter every 6 months.
• 5W-40 Rotella every 7K miles or so…

I haven't:

• Cleaned the MAP sensor since I got the GDE Tune
• Checked the function of my EGR valve since I got the GDE Tune.
• Checked wheel rotation being affected by sticky calipers.

I have surf racks on the thing, but do they offer up that much drag??? Curious to hear your thoughts.

hucorey · **Joined:** Tue Mar 06, 2012 4:29 am **Posts:** 378

Alternator decoupler will definitely cause a few mpg decrease. Boy mine sure did. Was only getting 25. Now I'm back to 31-32.

Have you changed your fuel filter?

65Corvair · **Posted:** Tue Sep 30, 2014 11:08 pm

Possible boost leaks around the intercooler?

I have that problem, one side is "wet" with oil.

usa591 · **Posted:** Wed Oct 01, 2014 2:12 am

hucorey: haven't changed the filter in a while--good call.

65Corvair: I'll check the intercooler

SFHLibertyCRD · **Posted:** Sun Oct 12, 2014 11:08 pm

I'm in LA and having similar issues. My commute is about 5 miles each way, but we also have other mixed driving, and my last tank was bad (see my fuelly for the trend). I emailed with Keith a bit and he suggested it could be transmission related when there is seemingly nothing else clearly wrong.

tjkj2002 · **Posted:** Mon Oct 13, 2014 6:00 am

usa591 wrote:

Could my relatively short commute be the reason? .

That is your reason.3.5 miles,even on at highway speeds,is not near enough time to get the rest of the drive train up to operating temps which effects mpg's as well.

mass-hole · **Posted:** Mon Oct 13, 2014 9:04 am

tjkj2002 wrote:

usa591 wrote:

Could my relatively short commute be the reason? .

That is your reason.3.5 miles,even on at highway speeds,is not near enough time to get the rest of the drive train up to operating temps which effects mpg's as well.

Seriously. My engine isn't even at temperature in 3.5 miles in the morning.

weeks101 · **Joined:** Mon Jul 30, 2012 3:29 pm **Posts:** 747

tjkj2002 wrote:

usa591 wrote:

Could my relatively short commute be the reason? .

3.5 miles,even on at highway speeds,is not near enough time to get the rest of the drive train up to operating temps which effects mpg's as well.

Agreed.

usa591 wrote:

I haven't checked the function of my EGR valve since I got the GDE Tune.

If it's sticking open you'll lose power and MPG.

Tree Catcher · **Posted:** Mon Oct 13, 2014 9:05 pm

I am also in Ca and have noticed that my mileage is in the crapper for short drives. Its been going on for about 3 months now... Possibly related to some wierd ca.
emissions messing with diesel???

racertracer · **Posted:** Mon Oct 13, 2014 9:24 pm

your disk brakes are stuck.. many just need the pins greased others need the rusted out pins replaced.

graycenphil · **Posted:** Mon Oct 13, 2014 9:31 pm

Most diesels get much poorer mileage when they are cold. If your prior driving was long trips, that will explain most of the decrease. If your prior mpg measurements were on the same short trips, it must be something else.

usa591 · **Posted:** Tue Oct 14, 2014 3:15 am

Quote:

If it's sticking open you'll lose power and MPG.

How do I check for EGR open/closed-ness? I found the unit on the side of the engine and the solution isn't jumping out at me.

SFHLibertyCRD · **Posted:** Mon Nov 24, 2014 7:50 pm

usa591 wrote:

Quote:

If it's sticking open you'll lose power and MPG.

How do I check for EGR open/closed-ness? I found the unit on the side of the engine and the solution isn't jumping out at me.

Hey man, any updates on this? Anymore leads?

CGman · **Posted:** Tue Nov 25, 2014 10:41 am

I'm having similar issues, but i have been making a lot of changes ( that should be increasing MPG) and now the weather is cold, so I'm waiting a little while longer to publish anything. But i will say a year ago i was indicated 28 MPG, actual 25 MPG; now I'm indicated 25 MPG, actual 20ish. :furious:

flash7210 · **Posted:** Tue Nov 25, 2014 1:24 pm

the only way to really know your MPG is to log each and every fill up for several months. Then calculate your average.

I thought my fuel mileage was slowly going down too. Then I did a long trip, all highway, and got 29 mpg. Then the next tank, mostly city, was 24. The next, mixed driving, was 26.
The next was 25, and so on...

All in all my average was 26 mpg. Same as it has always been for years.

All the time people say "I drove from A to B and got 32 mpg!"
But you only hear about that one time. They never post long term results and somehow forget about that time they spent a week off-roading in Moab and only got 22 mpg.

Lots of thing will effect you MPG. Such as:
Summer vs winter weather.
Fuel quality.
Condition of your air filter.
Tire pressure, size, and type of tire.
Highway vs city driving.
That time you woke up late and were stressed about getting to work on time while fighting rush hour traffic.
The weight and strength of your right foot.

mustang_gt_350 · **Joined:** Tue Jun 01, 2010 8:47 am **Posts:** 191

What temp is the coolant running?

usa591 · **Posted:** Tue Nov 25, 2014 6:52 pm

mustang_gt_350 wrote:

What temp is the coolant running?

I replaced my thermostat last year and since then, the indicator has been pegged to one click to the left of top dead center after it warms up.

Fuel economy is slowly going down...

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