My 99 v70 fwd non turbo wagon use to get 28 to 30 mpg on the highway. Now it is only get 23 tops. My car has 156k and it runs perfect. Plugs have been changed, air filter clean, oil is changed every 3k, use the same oil and it runs perfect. Tires good with proper pressures. No power loss. This is a mystery. Anybody have any tips on what else to check? Thanks

 

Anybody have any suggestions what I should check?

 

I guess I am on my own on this one.

 

Somehow, I can finally log in. Two things come to mind. Fuel and alignment.
Fuel for winter in some areas is low-energy content per gallon winter blend. Like gasohol, it contains less energy per gallon than summer blend so you can't help but get lower mpg. Law of thermodynamics or something like that.

Alignment out of whack can also decrease mpg.

You may also have mass airflow sensor troubles, or troubles with sensors re temperatures which will make EFI act essentially like an old-fashioned choke isn't fully opened. Too much fuel dumping in per cycle. But I can't diagnose
that -- you need electrodiagnostics.

 

Do you have a check engine light on for an O2 sensor? My upstream, or bank 1 sensor 1 oxygen sensor tripped a check engine light and I ignored it until my fuel economy went down.

 

Dropping from about 28 to about 23 is a drop of almost 25%. Just a change from 28 to 30 is almost a 10% change, and I'd be concerned about that. You shouldn't get a 10% change in MPG in normal use under consistent conditions (same road, same weather, same time of year).

From what I've read, changing from summer to winter blend should only account for less than a 5% change in milage.
And I would have to guess that it would have to be way out of alignment to account for a 25% drop. Same for tires - they would have to be way under inflated.

Clogged catalytic converter or smashed exhaust pipe?

How was you previous milage calculated?

I also had an air mass meter crap out on my old '95 850 T5-R, and it never tripped a check engine light. But it idled rough, wouldn't accelerate and the MPG dropped like a rock.

My '00 V70 R AWD consistently gets 21MPG for all around average driving as calculated by the trip computer. I can get up to 24 or so on pure highway driving. And, while I can't really see the MPG change with the winter to summer blended gas - I know it's there.

I wish I could get closer to 28.

 

I have come to believe that as engine gets old it drops MPG.
I have a 1998 Volvo V70 that had 130K miles when I bought it, it gave me constant 380 to 400 miles per tank in the city. I know this because each time I fill the tank (about 17 gallon) I reset my tripodometer to zero, now my car has 169K miles, and those 380-400 miles are gone forerever. all I get is 300 miles per tank
or you may say 17 miles per gallon where it use to give around 23 miles per gallon city miles.
Looking to get a lesser mile engine.

 

Yes, and No.


As the COMPONENTS of the engine age (plugs, MAF, O2 sensors, cat, etc) your mileage will decrease. With regular maintenance you should stay at about the same fuel economy. Regular oil changes also affect mpg.