Drop in MPG's - What to look for?

I've noticed a steady decrease in mpg's over the last few weeks. This is accompanied by a higher-pitched "hum" from passenger side - I haven't established if it's in the front or the back yet. It's pretty constant at most speeds. It's not grinding, so I'm ruling out seized brakes for now. My first thoughts are wheel bearings. I haven't pulled the wheels of yet to check, but once I do that, is there anything else I should check for?

I've dropped approximately 2-3 mpg's per tank... every tank for the last few weeks. Ideas?

Hub bearings
Dragging brakes
binding CV's
Binding front driveshaft
Binding rear driveshaft
T-case not fully disengaged
Low gear oil in F/R diff
Dragging A/C clutch

To check the hub bearings jack wheel up and grab top/bottom of wheel and try to rock,if any play is felt(in the up/down way not left/right) that bearing is shot of course after you rule out the UBJ and LBJ's.

When was the last time you replaced.........

Spark plugs
PCV valve
Fuel filter
Cleaned fuel system(seafoam or such)
Serp belt and tensioner

tjkj2002 said:

Hub bearings
Dragging brakes
binding CV's
Binding front driveshaft
Binding rear driveshaft
T-case not fully disengaged
Low gear oil in F/R diff
Dragging A/C clutch

To check the hub bearings jack wheel up and grab top/bottom of wheel and try to rock,if any play is felt(in the up/down way not left/right) that bearing is shot of course after you rule out the UBJ and LBJ's.

When was the last time you replaced.........

Spark plugs
PCV valve
Fuel filter
Cleaned fuel system(seafoam or such)
Serp belt and tensioner

Click to expand...

Dragging brakes - will check
binding CV's - these are new on the front end, and are only a couple months old.
Binding front driveshaft - will check
Binding rear driveshaft - will check
T-case not fully disengaged - will check - how do I know this for sure?
Low gear oil in F/R diff - changed 3 weeks ago
Dragging A/C clutch - will check
Spark plugs - changed 2 weeks ago - gapped at 0.040 per spec.
PCV valve - changed with spark plugs
Fuel filter - never done since I've owned the vehicle
Cleaned fuel system(seafoam or such) - done 1 week ago

All of these things above will cause the humming in question, too? I ask because it's at the same time I heard the noise that I noticed the drop in MPG's... so I assume it's connected. I'll check these other things though, and double check the fluids in the F/R diffs and t-case to be sure.

One way you can check wheel bearings is go into a parking lot and crank down your window and make a tight turn slowly and listen and if the noise gets louder during the turn it is a wheel bearing. A real tight turn puts more stress on the wheel bearings. So if you have one acting up it will get louder during the turn and when you streighten out it will lessen. You can do a tight turn to the right and straight and then do one to the left. I hope I am explaining this right.

Also you might be getting "winter gas" now depending on your area and that might have something to do with it.

Dave

Has your right foot gained any weight recently? Emptied all the dirt from your right shoe since the last wheeling trip?

Probably trivial and not having anything to do with the unique problem,

but how about the re-formulation in winter gasoline ?

The colder weather can have a roll.

The cold weather drops my mpg atleast by 2mpg during the winter season. I avg about 16-18mpg in the spring/summer season. Fall/Winter I drop to 14-16mpg.

jeepmedic said:

Probably trivial and not having anything to do with the unique problem,

but how about the re-formulation in winter gasoline ?

Click to expand...

You shouldn't see a dramatic drop. Maybe a mile per gallon.

All very valid points. If not for the humming that I hear from the passengers side, I would likely chalk it up to fuel.

JJ - nah, quite the opposite of lead foot here. I think the old blue-haired ladies are passing me in their Buick's for the way I drive. I gotta keep the rpms down as much as I can to up the mpg's.

Dave said:

One way you can check wheel bearings is go into a parking lot and crank down your window and make a tight turn slowly and listen and if the noise gets louder during the turn it is a wheel bearing. A real tight turn puts more stress on the wheel bearings. So if you have one acting up it will get louder during the turn and when you streighten out it will lessen. You can do a tight turn to the right and straight and then do one to the left. I hope I am explaining this right.

Dave

Click to expand...

Makes sense. I'll try this.

Maybe you just filled your gas tank with crap gasoline!

i have also noticed a drop in MPG's over the past 2 weeks. I attribute it to cold weather. The colder then engine is, the longer it takes to reach operating temperature, so you will either idle longer to get it to warm up (0 MPG) or drive on an "open loop system" (o2 censors not hot). which will result in much lower mpg's than when at operating temperature. Winter blend gas may also have a hand in the drop.

Hey Im new here just wanted to say I have gone from 16.9 a few months ago to 12.6 today. I have not changed my driving style, I would be ok if could get at lesat 15

Since gas prices have dropped, I'm not so concerned about the drop in mileage. It's still disappointing to see, yes, but I'll deal with it for now. If it doesn't pick back up in the spring, then there will be more questions.

Thanks for the suggestions.

If you happen to find out why your milage has dropped let me know ok!

Well on my 06 I noticed my milage drop also. I hear a noise coming form the rt side also, but it is the ac compressor turning on and off, I thought It was only in the defrost and AC mode that it does this but mine does it when in heat mode, is this normal for the Jeep. No other car ive owned does this. Is this unique to Chrysler products?

Check your EGR valve. That would decrease your gas milage because it wouldn't send fumes to be reburned. An EGR valve misfunction would be indicated by a check engine light. On our Durango it did sound a little different. I have a question: would an EGR valve be covered under warrenty? It is the only only thing NOT covered under emissions warrenty, and it costed be $250.

yellocoyote said:

Since gas prices have dropped, I'm not so concerned about the drop in mileage. It's still disappointing to see, yes, but I'll deal with it for now. If it doesn't pick back up in the spring, then there will be more questions.

Thanks for the suggestions.

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Yea, your Jeep will be all better in the spring.

Right now with all the below zero weather here, winter blend gas, and snow and ice, and running in full-time 4wd all the time, and never shutting the motor off because I have the heater set on the "roast my hemmeroids" setting, mine is so bad I am embarrased to post it.......ok - ok .....I'm getting around 13 combined right now on the last tank.

Dave

Dave said:

Yea, your Jeep will be all better in the spring.

Right now with all the below zero weather here, winter blend gas, and snow and ice, and running in full-time 4wd all the time, and never shutting the motor off because I have the heater set on the "roast my hemmeroids" setting, mine is so bad I am embarrased to post it.......ok - ok .....I'm getting around 13 combined right now on the last tank.

Dave

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You know, to be honest... I quit keeping track of my mileage this winter. I hated seeing the low, low average all the time. I'm living in 'ignorance is bliss' till spring.