MPG's go DOWN after smaller tires?

[coulrophobian]

I recently replaced my 33X12.5's with 31X10.5's and I get worse mileage... yeah, WORSE!! I've also noticed that it "hiccups" every now and then, almost like a cylinder is missing. My first instinct is to check the compression in all cylinders and go from there. I do know that I may have a lifter collapsing as evident when I was adjusting the valves. It's pretty gutless when I put my foot into it and seems I have lost quite a bit of power since the tire change, but it just doesn't seem right. Another thing, I was driving down the freeway the other week and smelled burning oil all of a sudden, pulled over and noticed that the oil pressure sensor was "puking" oil, got a tow from the old man, changed out the sensor and all is well. Any suggestions on ANYTHING???!!! I'm lost and frustrated. Thanks.

 

[srteach]

Without other changes to the drive train, your mileage will go down. It's expected. You should get slightly more power, but the smaller circumference of the tire will cause the tire to turn more rotations per mile. The engine works faster, with less effort, and burns more fuel because of higher RPMs.
Collapsing lifters can cause many of the things you are describing.
Check for loose wires and electrical issues for the hiccup.

Sorry I'm not much help.

 

[shane96ranger]

Without other changes to the drive train, your mileage will go down. It's expected. You should get slightly more power, but the smaller circumference of the tire will cause the tire to turn more rotations per mile. The engine works faster, with less effort, and burns more fuel because of higher RPMs.
Collapsing lifters can cause many of the things you are describing.
Check for loose wires and electrical issues for the hiccup.

Sorry I'm not much help.

I disagree. He should get better mileage at freeway speeds. The reason you would feel more power is because the motor is working less. My Explorer had a collapsing lifter and it did not affect mileage at all. If I had to guess, I would say you probably did not recalibrate the speedometer? This is where I suspect your mileage loss is. You are getting a false reading.

 

[coulrophobian]

Speedo has never been recalabrated. I haven't calculated the mileage, but I can tell just by paying attention to how much gas I'm putting in to it. What types of issues would cause mileage to drop, and/or fuel to be used so quickly?

 

[shane96ranger]

Speedo has never been recalabrated. I haven't calculated the mileage, but I can tell just by paying attention to how much gas I'm putting in to it. What types of issues would cause mileage to drop, and/or fuel to be used so quickly?

Lots of things. Are the new tires inflated properly? The local Big O likes to under inflate tires here. If it's in need of a tune up that would cause it too. When's the last time you changed your air filter? Fuel filter? Cap, rotor, plugs, wires, and timing will all affect it as well.

Like I say, I have a hard time thinking it's the collapsed lifter. Does yours ever shut up? Mine would start working better after it warmed up and got some oil moving but still ticked. My 91 Explorer (4.0 & 5 speed) with 240,000 miles still got 18-21mpg with the bad lifter. My 96 Ranger (4.0 & automatic) I replaced the Ex with gets 16mpg.

How big of a difference in mpg are we talking?

 

[coulrophobian]

I I take pretty good care of it. I have a cone filter that I just cleaned and oiled. Cap, rotor, plugs and wires only have about 2000 mi on em. Also just changed oil. Only thing I haven't changed is fuel filter. We'll see what that does. Tick shuts up like you said, after getting warmed up, except at higher RPM. And tires are at 35psi. I'll have to calculate mpg, but I think I was only getting 14 before I changed tires. I'll keep ya posted.

 

[coulrophobian]

By the way, does anyone know what the capacity of the fuel tank is on my truck? 89 2.9 V6 2wd standard cab 5 spd

 

[RustedRanger]

Did you unhook the battery to "clear" the computer after the changes?

 

[coulrophobian]

Nope. I'll do that as well. Thanks. I'll hopefully have an update later today

 

[RustedRanger]

One day I put some Restore in the oil and Lucas cleaner in the gas and it ran worse....until I unhooked the battery for awhile,then it ran better than it did before adding the stuff.

 

[robertc1024]

By the way, does anyone know what the capacity of the fuel tank is on my truck? 89 2.9 V6 2wd standard cab 5 spd

I think my '88's is 14 gallons.

 

[hidesertrat]

My 87 has a 14 gal tank and gets about 14 MPG. You have to take in account your driving habits too. If I am out and about, feeling frogie, it is real easy to drop MPG down to 11 MPG.

My kids to the same thing.
"Dad my car is getting bad gas mileage."
"How do you know that?"
"Cause I have had to put gas in it twice, when I usually only do it once."

Not ever considering they have made 15 trips to the store, 20 trips to town and let one of their friends borrow the car for a "quick" trip somewhere.

Best to keep a record of your MPG for three or four fill ups, so you kind of get an average. Some days are better than others.

 

[coulrophobian]

I filled up my tank when I thought I was pretty much empty (my gas gauge is another story) and I was able to shove 15.8 gal in it so I figured it was a 16 gallon tank... does this sound right? With that said I was able to go 300 + or - 15 miles (again, I'm not quite sure when my tank is empty because of the gauge) which would come out to about 19 mpg. Not bad... if my numbers are right. Fuel filter seemed to help significantly, however I never disconnected the battery. Will do it another day.

 

[HareRazor]

A more accurate way to figure out your gas mileage is to fill up. Write down how many miles are on the odometer or if you car has a trip odometer reset it back to zero. Drive. Fill it back up and write down miles and how much gas you put in. Miles driven / gallons = your gas mileage.

 

[bobbywalter]

I disagree. He should get better mileage at freeway speeds. The reason you would feel more power is because the motor is working less. My Explorer had a collapsing lifter and it did not affect mileage at all. If I had to guess, I would say you probably did not recalibrate the speedometer? This is where I suspect your mileage loss is. You are getting a false reading.

smaller tire give better mileage if it was indeed calibrated to 33 tires.

if this truck has stock gears and he is getting 19 mpg, he is likely getting 21 plus in reality...which is par.