(Please don't move this to Wheel & Tire, as I am not 100% sure if we are talking about a tire issue here)

Okay, so I am not a mileage nut like some people, but I do like to keep track of how many miles I get with each tank of gas. I simply reset the trip meter at each fill-up and I always let the tank drain down to almost being empty. This lets me mentally determine what is a "good tank" and what is a "bad tank", and contributing factors can include the type of gas, trip length, driving style, etc.

Well, recently I have had some extremely "bad tanks" by my personal standards. I know that for some people, getting about 300 miles per tank is normal. For me, this is not normal at all. I have consistently achieved 360 to 380 miles on every tank, and I have always felt like I could push 400 if I really drained the tank to empty. Unfortunately, the last four tanks in a row have all been about 300 miles or even slightly less. For me, this represents a sudden loss of about 80 miles per tank at the least, or a loss of about 6mpg.

So now I want to try to figure out what is causing the sudden bad fuel economy. Right before all this happened, I was due for an oil change and a brake job. I was also due for new tires (they were getting really bald). I had been putting off these maintenance items until one day when I literally heard my front tire hissing at me after I stepped out of the car. I could actually see the tire getting flatter, so I quickly drove two blocks (carefully) to the local Just Tires store. I decided it was best to get a new set of four tires, since they were all in bad shape. I ended up settling for a set of Dunlop Direzza DZ101s in the stock size. After now having had time to test them out, I can say they feel much better than the stockers ever did.

So anyway, I don't know much about tire brands and types, but I do know our tire size and I can confirm I got the right size and I inflated them to the right pressure (as per the new tire specs, not the stock tire specs). I have a basic understanding of the concept of rolling resistance, and I would understand if these new tires robbed me of a little bit of fuel economy. However, a full 80 miles less per tank of gas? I doubt this could possibly be attributed to the tires alone.

So unrelated to that, I went to take care of my other maintenance issues on the same day right after I got the new tires. I got an oil change from EZ Lube for $19, but I doubt that could have any correlation to my bad mileage. I also got a front brake job that day from the dealership (resurface rotors, replace pads, oil calipers). I also requested that the dealership retorque my sway bar, strut bar, and suspension bolts, and top off my other vital fluids. I got an alignment done too, and it was noted that the toe on my right-rear wheel had been way off. Still, I don't think any of these items are related to a loss in fuel economy.

So what's the deal?

 

wow. 380/tank? Are you mostly highway?

 

I started a mileage thread a couple of months ago about who had the "most miles on a single tank". I was proud of my high gas mileage. It wasn't the highest by any means, but it was pretty good by most standards. I drive almost entirely on the freeway and I have an intake and grounding kit (if you believe in that stuff). So yeah, 380 per tank was absolutely normal for me before, but today my mileage just sucks.

 

Wow. my reserve light usually goes up at around 200-220 miles. I better clean out all those rocks in my shoes lol. Have you checked your filter? Possibly getting a bad batch of gas if thats possible? I know on my road trip from NY to FL I filled up at this really sketchy gas station and my car most definitely felt alot more sluggish after that fill up. Luckily most of that gas should be burned by now.

 

if the tires are the same size as the OEM tires, you should fill them up to the reccomended factory specs set by toyota.

also, make sure they are 100% correct size or the car, make sure the aspect ratio is correct, maybe they gave you tires that have alittle more sidewall, so your covering more distance, but your odometer is off.

have there been any major changes in climate, getting cooler, hotter, more humid, etc.

could the ez lube place used oil that was thicker than oe specifications so it is taking more energy to pump it around?

 

200 -220?? that's not normal. I get a little below 300 just in city.

 

wow 380 a tank.. I only wish I could get that kinda mileage and I would say that im mostly highway. but since ive owned my tc from day one I was averaging 260-280 a tank. the most I've ever gotten was 350 and that was going to santa barbara and letting the tank go to almost empty. now I put an intake and I lost about 50 miles. im getting about 210 to the quarter line.. about how many miles do you drive a day? im about 40-50 a day..

 

Not bad gas since it's been several tanks and I always fill up at Mobil or Shell. I haven't considered checking my filter, so that might not be a bad idea. However, I do think the tires are at least partly to blame.

 

150 to 200 daily.

 

Your intake cost u 50 miles? that makes no sence....

 

I do tend to have a heavy foot tho. One time i went very easy for one tank and managed 280 out of it, but that was boring.

 

I like the way you think. I must admit, I had never thought about this. The new tires are slightly bigger than the old ones, BUT they are the same size (215/45 R17). The larger size seems to be in the tread. They must be a different "type" of tire, despite having the same size specs. I know the new ones are bigger because they hit the inside of the wheel wells when I go over dips. This happens about 4 or 5 times on my daily 101-405 commute.

Like I said, they are definitely the same size as the old tires, but now that you mention it, the extra tread depth could be making enough difference to throw off my odo. Good call.

I also wondered about this too. I hope those guys didn't screw up and use the wrong oil. I have noticed that it seems to take more gas to pull the car up a hill or to accelerate from a stop, but in my mind I have been attributing this to having stickier tires.

 

The extra tread depth would not be making anywhere near that much of a difference in mileage.

Check your pressure. Should be at vehicle recommendations if the tire size is the same.

 

Well, here's the thing. I believe the stock tires are supposed to be inflated to around 32psi. I always had my stockers at 34psi and I checked and topped them off regularly. All of my "good tanks" were recorded with a tire pressure of 34psi all around.

With these new tires, the "max load" on the sidewall is 52psi, which is a bit higher than the max rating of the stock tires. For that reason, I decided it would be safer to go higher than 34psi with the new ones, in the interest of improving mileage. I started out at 36psi in the new tires, and now I have them at 38psi, but this has done nothing to improve my mileage. I also know that going any lower will certainly cause my mileage to worsen, so there is no point trying to go all the way down to 32psi (the vehicle recommendation).

 

I don't know if they do this in CA, but here in AZ the summer gas is like 15% Alcohol. Gas mileage in my car went down from the 370 range to about 320 from a tank. I also noticed that it no longer matters if I use higher octane vs lower octane, I get about the same miles. When the "winter" gas is here, I can consistently get 370 from 91 octane and about 350 from 89, 330 from 87. Now I get 320 or slightly lower with nearly any octane reading. The only other things I can think of is things like dirty air filter, tire PSI, and that sort of thing. I don't think the oil would be that big of a difference in mileage. In other cars that I have had I have run different oils and never saw a notable difference in mileage. I was running 0w20 in my tC but now run 5w20 and see the same miles. The only thing I have seen in my case is the "summer/winter" gas.

I hope you get it figured out.

 

Well OEM pressure should be 32 up front and 29 in the rear. And measuring should be when cold (preferably in the morning before driving on them at all). One extra psi wouldn't be a bit deal... but I wouldn't be changing them too much.

 

A sticking caliper or dragging brake pad will cause lowered gas mileage, but you would feel it when you brake and it would give off heat after a drive. Just a thought...

 

Not sure how to recognize that. I mean I don't feel any major difference in how the car brakes. It seems to be smooth and normal, but the car feels like it takes slightly more effort to move it forward.

 

You can certainly lose mileage due to new tires. Added tread depth (probably around 11-12/32") will cause more rolling resistance than an almost bald tire. Also, it's very likely that your new tires are more performance oriented and have a softer compound; again, more rolling resistance. They could also be heavier than the OEMs to that decreases mileage too. Finally, OEM tires place fuel mileage really high on their list of priorities and will sacrifice other things to achieve that. Most aftermarket tires put performance as the top priority, so some of the others things suffer to achieve that goal.

 

Hmmm, let's see if anyone else noticed this... every time I had the dealer change the oil in my tC (the first three were free), they put in synthetic. I asked every time and they put in 0W-20, and they said that the oil they used was made by Mobil.

Since then, I've always put in Mobil 1 synthetic 0W-20 and my mileage has been consistent, with only light variations due to my driving habits. Now, I usually don't trust those EZ-Lube joints and I kinda doubt that they used synthetic on a $19 oil change.

One more thing... Most will usually say that once you had synthetic in your motor, you shouldn't go back to regular. Hmm...