Hi Folks, I have a 2006 S60 2.5T that is approaching 170,000 miles, and I've noticed my fuel economy dropping. I've recently changed the plugs and coils, and I'm always keen on keeping my tire pressure consistent. Would replacing both O2 sensors along with the MAF sensor help my fuel economy?

 

really depends on how far it has dropped. Replacing the rear O2 sensor does nothing - that's there to measure the efficiency of the cat. The front is the lambda sensor regulating fuel trim. If the front sensor is bad, usually it results in a CEL and a big drop in MPGs. Two things I'd try 1) cleaning the MAF with MAF cleaner (some carb cleaners are too harsh) as well as the intake path 2) drop in some injector cleaner like Techron in the gas or consider having the injectors cleaned by a cleaning service or a jewelry cleaner). Another option here is to run a brand name premium for the next couple tankfuls. If you are mechanical, you can also measure your engine's compression. if you find its less than 150 psi (for turbos - NAs should be 180+ or so) across the board, you may be fighting a losing battle. Have you noticed surging or hard starts etc? If so, you may want to check fuel pressure as your sensor/pump may be a bit off.

 

I've been running Shell Premium for the life of the car, and have not noticed any surging. I've had intermittent hard starts, where the starter will just stop cranking and then resume. I used to average just under 25mpg but now I am around 20.

 

Ok let's assume it's not the summer blend of gas giving you this alleged 5 mpg decrease and a new air mass meter and front o2 sensor would bring back the 5 mpg, ignoring age of engine/car/different routes taken/etc.


For $3 gas, 25mpg is 12 cents a mile, 20mpg is 15 cents per mile - 3 pennies difference.

A quality air mass meter is ~$150, a quality o2 sensor is ~$140 for a total of ~$290 if you do the work yourself. 3 cents a mile gained with $290 in parts.


IF those parts help - you will break even in 9666 miles. (if i did the math correctly)

OR - those parts don't help and you have wasted ~$300

 

That's a good point, also taking into consideration that the A/C compressor is running all the time also.

 

For me it would not be a question of cost savings, more of an indicator that something else might be going wrong. Not saying it is, just saying it's not a bad idea to track your mileage closely for just such a reason: to get an early sign of a bigger problem that might get worse and that you can take care of early before it gets really expensive.

 

rounding error...9667 miles

The ghost of your grade school math teacher

 

(math major here)