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On my Dodge Durango with Scancage I was able to AVG about 18.5 MPG to San Francisco but on the way back same route I was able to get only 8.5MPG with ScanCauage. On the way to SF I filled up regular so...don't know if it could have caused the problem.
In city I am now getting only 6.5 MPG instead of regular 10-13MPG

Here is what I did to correct it but no luck.
-Took out my K&N filter, washed it with hot water & dish souap.
-Vacumed the filter box...

But it's not making any difference. What else can I check, this is horrible.

Thanks.

Is the engine getting up to normal operating temperature? Is the check engine light lit? Have you checked for stuck brake calipers?

Did you adjust any of the ScanGauge settings when you filled up?

How many miles are on the truck?

I'm wondering if Sean might be on to something. If the engine size were to get reset to factory, the SG would report your 5.7L engine usage as though it were only a 3.0L.

Is the engine getting up to normal operating temperature? Is the check engine light lit? Have you checked for stuck brake calipers?
Yes, engine heat is normal, not overheating.
No check light
how to check if stuck brake calipers?

How many miles are on the truck?

75K

what else to check?

has it been really cold lately?

My numbers dropped from 20-21 on the hwy to 16-18 because of the cold mornings.

Otherwise if you changed the fill numbers when you filled up last on the SG it will effect how accurate it reads milage, fuel usage, and thus MPG's. If it was changed just go in and change it back to around the same % it was before.

I'm not concerned about overheating as much as I am concerned about the engine being too cold. If a thermostat gets stuck open the engine will have a tough time warming up, potentially causing it to run rich and kill your gas mileage. Use the SG to find out what your peak engine temp is and how long it takes to get there.

The easy way to check for a stuck caliper is to check the temperatures of each brake disc after an extended highway run. The preferred method is to use an IR thermometer to look for one disc that is significantly hotter than the rest. The "poor man's" method is just to hold your hand some distance from each caliper (don't touch anything! even the wheel) and see if you feel heat coming off of one of them. If it's bad enough to halve your fuel economy then it will be completely obvious and the destruction of that disc won't be far behind. On the other hand, I would be surprised if you hadn't smelled it cooking by now.

has it been really cold lately?

My numbers dropped from 20-21 on the hwy to 16-18 because of the cold mornings.

Otherwise if you changed the fill numbers when you filled up last on the SG it will effect how accurate it reads milage, fuel usage, and thus MPG's. If it was changed just go in and change it back to around the same % it was before.

I understand cold affects it..but I live in CA so it's not that cold.

Brick - I do not smell antything b ut I'll check the heat level. Thanks.

You haven't mentioned whether you changed any settings on the SG?

Refill the tank if you haven't in order to confirm mpg per scangauge?

You haven't mentioned whether you changed any settings on the SG?

Have not changed anything in SC the only I did when I refilled last time on the way to SF was to set the Fill Up amount/gallons and price...like I usually do to callibrate.

Perhaps something wasn't keyed in quite right for the fill up? My guess is that your fuel offset is rather large right now.

Did you fill up with out-of-state "dirty gas" when you got your good mileage, and then with CA's RFG for your new crappy mileage?

Is the AT no longer locking up?

Did you lock the front hubs and never unlock them?

E-brake stuck on?

Hooked up a trailer and didn't mention it? Put 2000# of cargo in the back and forgot to mention it?

-soD

Chrysler is famous for stuck calipers. A mechanic told me it is because they use phenolic pistons. Whether you have one or more stuck calipers or the E-brake is stuck "on", a few miles on the highway and then a stop & sniff will tell you if this is a problem - burning brakes are pretty stinky. My old convertible developed this brake issue a few years ago, and after about three miles, you could really smell it inside the car. The brake pedal was unusually hard and the car didn't seem to want to stop. When I pulled into a lot, I could see a little smoke coming from the calipers - after only 3 miles of around town driving at <= 35mph. As the brakes heated up, they faded and so there was no dragging effect - the car would glide pretty well even with the front brakes "on". But the heat generated had the wheels feeling very hot to the touch and the tires were much firmer than usual. Long story short - if the brakes are seriously dragging, you'll know about it.

Considering the mileage on the odometer, you may also want to check for the equally famous Dakota/Durango ball joint issue. If the ball joints are just about gone, the resulting odd camber and toe will cause the tires to be rather warm after some highway driving, and steering will seem 'wrong'.

Although the two issues above can cause increases in fuel consumption, it is not likely to add up to the 50% loss you noted. If you have 4WD, confirm that the transfer case isn't binding. Are neutral (or off-throttle) glides much shorter than normal? If you turn in a tight circle, do the tires chirp or does the truck hop?

If the car coasts normally, the issue is with engine management or SG settings. If the car does not coast worth a darn, the FE loss is due to something beyond the engine - transmission/transfer case/wheels/tires/brakes/alignment/etc.

With such an extreme change in FE, I'd expect the problem to be noticeable from behind the wheel - something like a loss of power, shorter glides, or a strange noise. If nothing seems strange except the reading from the ScanGauge, I'd suspect the gauge. Or perhaps you got a tankful of something dodgy when you last filled up?

Hope you solve the problem anyway.

-Simon

We still havent heard if the change is real or just the Scangauge?

You need to refill the tank and do the math on mileage vs gallons and see if its the instrument or the truck.

Speculation wont help until you make sure its a real:eek: problem.

Did you fill up with out-of-state "dirty gas" when you got your good mileage, and then with CA's RFG for your new crappy mileage?

Is the AT no longer locking up?

Did you lock the front hubs and never unlock them?

E-brake stuck on?

Hooked up a trailer and didn't mention it? Put 2000# of cargo in the back and forgot to mention it?

-soD

You have lots good points Dave.

Myabe gas was bad, I thinking about that tooo...I bot some fuel system cleaner which I'll put in a t refill.

No emergcy locks. and no trailers

What is AT? Automatic Transmission? If yes, how to tell if it's locking up o not?

Watch the tachometer as you drive. At low speeds, the rpm varies based on your gas pedal more than on the vehicle's speed. Above a certain speed (somewhere around 40 or 45), it should lock in and will no longer vary much at all, only slowly climbing with the vehicle's speed.

So have you checked to make sure that the mileage drop is real? That's probably the most important step anyone has suggested. There's no point troubleshooting before you confirm that the SG is telling a true story.

I am refuiling today to test.

One thing I forgot. I got really awesome mileage once going from Tahoe to SF. I was really psyched until I realized that the trip was very significantly downhill...

-soD

Im on the east coast here and havent driven out to SF. My question is what elevation change was there between the the start and the destination. Was it mostly down hill going and therefore more uphill coming back?
Bad gas is my next thought. Try looking in your fuel filter to see if it contains more than the normal debris. If you have to remove it to a glass container and let it settle you might see water in the bottom. You might need to change it more than once if lots of junk is in the tank.
Are you getting any ticking or clicking sounds under the hood that might be a loose or bad wire? I used to just wait until it was night time and look under the hood when I could see the bad wire arcing when the cylinder tried to fire.
On the bad caliper if you jack up one of the front wheels you should be able to turn it by hand. With caliper stuck you probably wont be able to turn the wheel. The back wheels will be a bit harder to turn but be sure to chock the front wheels to try this as you certainly will need to let off the parking brake to turn the back wheels.

I see no point in this discussion going any further untll the ACTUAL mileage is measured. Its been over a week and we still dont know if the mileage reported is an artifact of the instrument. There is no point in speculating until it is first determined that there really IS some:biglol:thing to speculate about.

I've had 02 sensors go bad before and cause a 25-35% drop in fuel efficency. It will usually cause the computer to set a code. but sometimes if it's just a lazy 02 sensor not making the changes a quickly as it should it won't set a code. A few other things to check are vacuum hoses to make sure you don't have a cracked vacuum line or one that has came off it's connection, start the vehicle up at night with the hood up so you can check to see if there's fire arching from any of the plug wires indicating bad plug wires. Might also give it new plugs to see if that helps or not.