Of threads on the board concerning gas mileage. I am wondering if anyone has any input on my situation specifically. I have spent hours perusing the boards looking, learning and performing tips from the other threads.

I have a 99 4runner sr5, w/ 136k
Current mileage I am getting is a bit less than 12.5 per gallon
This is very disconcerting as I have:

1. Treated it several times with seafoam (gas tank and PCV)
2. Used one treatment of Redline SI-1 (Gas tank)
3. Cleaned the throttle body
4. Cleaned the MAF sensor (very carefully)
5. New Plugs/wires (Denso - about 4 tanks ago)
6. New Fuel Filter (Toyota OEM - about 4 tanks ago)

I was up to about 15 mpg BEFORE I put the new plugs/wires on and the mpg has DECREASED since then back to sub 12.5 where it was when I first bought it.

What am I missing???!!!

I live in Chicago so the weather here right now is cold, but neither my wife or I have a heavy foot and we dont run the heater on high all the time, usually on low. We are getting about 180 miles in before we have to fill back up.

Is this normal?? I mean I can live with 15 in the winter, which means I should be looking at about 18 in the warmer weather I believe. To make this car affordable...I mean for me to want to sink the money into it for gas/maintenance I really would like to be averaging about 18 year-round.

What else can I do to improve this situation as it is really frustrating to be getting the mileage that the H2s get, but in a truck half the size.

I appreciate ya'lls input! Thank you.

 

I know the chemical make-up of the fuel changes in the winter causing lower gas mileage. As far as running the heater, that would have nothing to do with it, unless you are running it in conjunction with the A/C.

I would make sure the air pressure in your tires is above 30 psi. I run 35 in mine.

Also, if you haven't done so, change your air filter.

Have you changed your PCV Valve?

These are some commom factors to poor mileage.

 

I am going to check the tires today, good reminder.

I have not changed the PCV valve. Why would this possibly be a factor? I do not completely understand how it works.

So am I correct in saying that the AC runs on the gas, but heat is electric?

Thanks!

 

The A/C compressor will put more "drag" on the engine. I am sure you can feel the idle change when you turn the A/C on. IF the A/C button is not pushed in, then you are heating the vehicle with the heat off of the engine, this is "free" heat Now if you push the button in, then you are getting heat while taking humidity out of the inside of the vehicle.

Yeah check your tire pressure.

The PCV Valve, I changed mine at 60K. Has yours ever been changed? If it is clogged or dirty, it is not working correctly. I am not sure but if you do the seafoam you might want to check and make sure it is clean. I know you are suppose to change spark plugs after a seafoam treatment.

Also I have read where O2 sensors can cause crappy mileage...just things to consider

 

i'm willing to bet that it's the fuel composition that's screwing your milage. i believe chicago (and most of the midwest) runs a very high percentage ethanol blend in the winter. ethanol has less energy per unit volume than gasoline, so it's understandable that milage will go down. out here in colorado we run a 10% ethanol blend in the winter and i can always tell when the gas station switches over (the plot of my gas milage vs time is a step function those two times of the year).

also, as was said before, don't worry about running the heat, it just sucks the heat off the engine, it costs you nothing to run it.

 

I'd say you need to get your oxygen sensor checked/replaced.... you should definitely be doing better than that. When you changed your plugs were they uniform, I mean anything on the plugs that would raise a flag?

 

Thanks for the tips guys!

I will check out the PCV. Changed plugs after the seafoam so I am good there. I did not know about the fuel composition issue, thank you for the enlightenment.

Tried to take the O2 sensor out this morning...the two posts coming out of the exhaust pipe are practically rusted together with the bolts holding the o2 sensor on...not sure what to do there...talked to my mechanic who said he could try to get it off by heating it up with a torch, but these bolts are stripped and corroded big time. He said he has had those posts actually snap off before and has had to replace the whole section of exhaust that has the forward o2 in it. This particular 4 runner has been a huge pain...I love the 4 runner in general, but everytime I turn around I need to try to do something else to improve fuel economy and that step never really works...and on top of that I have the issue of not even being able to get the dang o2 sensor off...

any ideas? sorry for the mini-vent there...thanks!

 

Put some tabasco sauce on the threads, I have heard that works on rusted bolts. Or WD-40?

 

12.5 sounds really low. My old 3.0 got 17mpg average and my current 4runner gets 17 to 24

 

My truck spent it's first 4 years in the Chicago winters - it's STILL a beyach to work on!

When I first changed out my O2 sensor, I had the same problem. You have to use a deep socket or a box wrench, lots of PB Blaster (a penetrating oil) and patience.

Soak the nuts and studs in PB Blaster; wait 20 minutes; try some pressure on the nuts - NOT TOO MUCH; repeat as required.

Be careful when applying pressure - iof you snap the studs off, your next stop will be an exhaust shop to cut the pipe off, replace it and weld on a new bung.

 

huh-huh. You said bung!

 

Does the truck run well? What kind of plugs and wires did you use when you replaced them? If you went with aftermarket you may not have improved but may have made matters worse. Toyotas seem to like the Nippon Denso plugs.

 

I used Denso Plugs and Wires...These as well as the fuel filter were all OEM purchased right from my dealership where I got the truck.

So where can I get some of that PB penatrating oil?

 

Any auto parts store should have it. Schucks, AutoZone, Napa, etc.

 

I need to mention though that these bolts are literally rusted and corroded, the hex formation does not even exist anymore...so if and when I hopefully get these suckers off I will need to replace them, but I am not sure with what size...anyone know the standard size for those?

Man I just hope I can get them off. Thanks for all the tips!

 

Well,

The verdict is in, my truck is jacked up.

odometer reads 166.5 miles and the gas gauge is on E.

Full tank to E it only went 166.5. Now I know there might still be a gallon or so in the tank, but that only puts me right under 180.

What is wrong with my truck?? Should I just turn it over to a full time mechanic and see what they can find????? This low of mileage seems to be cause for concern to me, and I dont know if there is anything I can do as a armchair mechanic to really remedy the problem...that I have not done already.

 

Well, you and I are in the same boat. I'm getting about 180 miles to the tank these days as well and I can't figure out what's going on. It's been happening for months now.

One more thing for you though, are you running stock size tires? If you're running bigger than stock, then the "fixup" math will get you a few more miles per tank, but it won't get you back to where it should be.

 

My mom gets 260ish a tank from her '99 and I can never seem to get over 230 a tank which comes to about 16 mpg but I'm not gonna complain on this thread. I do have 31" tires but I still expect better;I'm doing new plugs next week along with a few other things so we'll see if that helps.

 

the combo of the midwest gas and the repeated seafoam treatments sounds like a def possibility. I remember reading lots of threads that fuel mileage went down after the seafoam because of the clogged 02 sensor. When the exhaust on my old car had to come off I had to use an air chisel and a sawzall to get the bolts of. the sawzall worked best.

 

You might try a propane torch on it to see if you can get it to loosen up a bit and use the PB blaster to quench the metal then heat again and repeat the cycle. After doign that a few times then soak it one last time and leave it over night. Then in the morning, use a pair of vice grips to see if you can get the nut to break loose. I bet you'll eventually get it to come loose. Then be sure to get new nuts from the dealer and use some antiseize to prevent it from happening again (do not get any on or near the tip of the new O2 sensor).