Fuel MPG Dropping

My 2012 Tacoma has 213,000 miles and it still drives great. The past couple of fuel fill-ups I’ve noticed my MPG has gotten worse. Where I would normally get about 110 miles on the first 1/4 tank, I’m now getting 85-90. There aren’t any dashboard codes and my driving habits haven’t changed. Do y’all have any suggestions for what I should inspect or replace?

 

The gauge can be getting less accurate with time. Stick to gas station calculations rather than the gauge showing an arbitrary measurement.

Spark plugs have short intervals though, and these trucks like the maf and throttle body clean, so simple maintenance is a good idea regardless.

 

Not really an accurate or recommended way to check your fuel economy. Way too many variables and no actual data. That being said, the usual things to check are if your truck has had a recent tuneup, are the air and fuel filters fresh and clean, are your tire pressures correct. Further, with over 200K miles you might need to check overall engine health with a compression and leakdown test. Just for starters...

 

Check you brake. 2 Month ago i found that i had 3 piston seized (1 front driver side, 2 front passenger side). The brake worked fine but the piston didn't retract correctly, they were rubbing on the rotor. On the highway i was around 17 Mpg before replacing the caliper. Now i can do around 20.8 mpg. My gas money was converted to heat at the wrong place.....

Get an ultragauge or scangauge if you want to monitor your fuel. An you need to use the same station with the same pump when you fill up if you want to be sure of your result when calculating MPG.

 

Here’s a post I made on this topic with suggestions to recover mpg:

https://www.tacomaworld.com/threads/mpgs.809605/#post-29039211

 

I have done the math and before I was getting around 17.8-18.2 mpg in the city. Now it’s around 16ish or even high 15 mpg.

I replaced the spark plugs this summer and cleaned the MAF and throttle body.

 

Maybe time for new O2 sensors? They can get sluggish with that many miles and contribute to incorrect rich/lean feedback.

 

Would I get a dashboard code if O2 sensors were going bad?

 

Yes, unless the problem is intermittent, but the code could be stored in memory regardless. 18mpg in the city would be good for me. I usually get 16 in city, 18 on the highway. You didn’t mention a new air filter but I’m sure you’ve checked that. You can spin each wheel to see that it spins freely. Any noticeable drag can point to worn out bearings and/or stuck caliper.

 

What engine and transmission do you have? This time of year I get a bit over 200 miles on half a tank, averaging about 22.4 with the 2.7L and 5 speed manual. My unusual commute is conducive to good mileage though, about 40% highway and the rest 45-50mph on hills.

In the winter it's around 19.75 mpg.

 

Not necessarily. The sensors can still "work" but with that many miles they might report inaccurately for the driving conditions.

 

Until you actually compute your MPG you know nothing. Saying how many miles you drive on 1/4 tank is useless info. And if you never did that previously you have no baseline to work from.

You may or may not be getting worse fuel mileage and even if you are it's not anything to worry about, yet. A couple of tanks is meaningless and 10-20 miles difference in 1/4 tank isn't much. Even though you think you're filling the tank the same every time you can easily be 1/4-1/2 gallon different. The fuel gauge will show full even though you can still get 1+ gallon in the tank.

Shorting yourself 1/2 gallon can reduce how far you drive by 10 miles. I tend to get about 100 miles in the 1st 1/4 tank, but that can easily be +/- 10-15 miles. Road, weather, and traffic conditions can change. You may need to add 2-3 PSI to your tires. You sometimes get fuel that is good or bad that can drastically change fuel mileage for a tank or 2.

The only number that matters is the actual calculated MPG's. In the years I've owned my truck that has varied by a lot. For everyday driving around 16-17 mpg is normal for me. On the road 18-20, but I've gotten as little as 16 and as much as 22. From Bryce Canyon in Utah to Denver I got 20, from Denver to KC I got 16. From KC the rest of the way back to GA I got 20. That was all in 2 days driving

You are probably seeing no more than 1-2 mpg change. And that much fluctuation is normal. Get in the habit of doing the math so you know where you are. Then if it starts changing you'll know if you have a problem. A few tanks with 1-2 mpg difference are nothing to worry about. But if it stays down for a long time, or if you see a significant difference then you need to start looking for problems

 

maybe gas stations are switching to winter blend gas. Maybe not.

35's might help

 

Like he said, do the math. I use a spreadsheet. In the dead of winter below zero, I've gotten mpg as low as the 9-ish, and in the warmer weather, the truck managed mid-23 mpg twice. The truck has a lifetime average mpg in the mid-18s and between the Ultra gauge and my spreadsheet, the difference is less than .4 mpg. City driving in the winter is not good for mpg.
The truck has stock running gear with all maintenance up to date with the exception of the front brakes, they need changing soon.

 

Basic maintenance could be the issue.

How old are your spark plugs, coolant, oil, tranny fluid, diff fluid, Case, etc.

Dirty intake and throttle body?

Old o2 sensors (upstream)?

When was the last time you ran fuel system cleaner?

All these little things can sneak up and ruin fuel efficiency

 

OP replace your PCV, it’s cheap and super easy to do, and improved my mpg, grease your zerks (not sure if this will help but I think it might) and I noticed that my mpg went up 1/1.5 mpg when I switched from 75/90 gear oil to what our manual recommends, 75/85, for the front and rear diffs that is. I may take some flak for this but I am obsessive about monitoring my mpg and can say emphatically it improved with a 75/85 (front/rear) switch.
75/90 goes in transfer case. I prefer Redline brand for all three.

 

I'm with the others who are suggesting calculating it on miles driven divided by gallons to refill, over a couple of fill ups.
As far as sticking brakes go, I don't know how often that actually happens to people, BUT...
I have an IR Pyrometer that I use to check hub and drum temperature from time to time. There's no specific number for which you should be looking, but they should be pretty close from driver's side to passenger side.
That would tell you if you have a brake sticking. You can pick one up for $20 - $30.

 

On mine, what made the most dramatic change in mpg is putting a new air filter in. It wasn’t that dirty, so it looked. It had been a couple years, maybe 8-10 k miles and I had a new one on hand so what the heck I figured.

Not driving with a lead foot also makes a difference. This is a habit I just can’t seem to break. So I regularly get 11-12 mpg. Every once in awhile a little less or more.

The times I got over 12 is usually because I drove it on the freeway.

 

I changed my spark plugs, coolant, oil (2 weeks ago), transmission fluid, rear differential fluid this summer. I drive a 2WD, so no transfer case. I also cleaned the throttle body and MAF this summer.

I haven’t changed the O2 Sensors and they’re OEM, I believe. At 214,000 miles, should I change them even without a dashboard code?

I’ve ran fuel system cleaner twice over the past couple months.

 

That’s the way I calculate my mpg, which is when I’ve noticed my mpg going from 18 to 15.5-16.5. I’ll look into if my brakes are sticking!