Subaru Forester Owners Forum banner

1 - 3 of 3 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter #1
Hi
I purchased a certified pre owned 2016 Subaru Forester Premium last month and noticed a sudden and large drop in my fuel economy. I live in Melbourne Florida so the weather does not change much within the past month. In order to try and objectively compare numbers, the following averages are for the same 120 mile drive on i95 without traffic.


My first tank of gas I got over 33 mpg highway and my last two trips averaged 24.5 mpg on the highway.
My average for both city and highway was about 26-28 mpg combined, now it is close to 21 mpg. The car has 35k miles and is still under bumper to bumper warranty. I know avg speed, tire pressure, wind, fuel T, etc all can effect gas mileage but this is a drop of almost 7-8 mpg, which I think could be indicative of something else. My gas mileage on the highway seems to be more affected.
I can take it to my local dealership but wanted to see if anyone else solved the same problem.
 

·
Registered
MY05 Forester 2.5 XT 5MT
Joined
·
2,738 Posts
After a long drive at 40mph+, do any of the wheels feel especially hot compared to the others? A sticking/binding brake caliper permanently applying the brakes on 1 corner could have that effect

Has the car spent any time where the roads are treated with salt/grit? A hole in the exhaust upstream of the oxygen sensor could cause sudden drop in mpg too. A leaking exhaust manifold gasket could cause this too. Quickest way to diagnose would be to use an emissions testing probe at the tip of the exhaust - If your state does emission testing like that......Or listening for leaks while under the car.

A faulty oxygen sensor could cause this too. I can't remember off the top of my head if you would be open loop or closed loop when cruising on the highway though.

A faulty fuel injector could perhaps do that too, if 1 is not fuelling, it would cause the other 3 to dump loads of fuel into the engine to try and make up for it, causing you a big drop in mpg but would give you rough starting typically too if it is cold - I guess Florida doesn't get that cold though ?

Is the check engine light on ?

Is there a particular fuel you use ?
 

·
Registered
1999 "L" - 231,000 mi. AT
Joined
·
715 Posts
Welcome to the forum - 1st post.

It's tough to get comfortable with a fresh car, I always look at one with an analytical eye. 7 mpg change is a large change. Are you filling it up after each 120 mile freeway trip? If so, try a month of filling it at 300 mile intervals.

If the dealer accepts your mpg data they'll probably do a tune-up and/or give you an inspection - my guess.

I've not found gas brand to make a difference. My old '99 has done reasonably well with mpg as it ages, despite CEL being on for much of the past 50,000 miles. Really only speed, headwind, in-town driving, consistency in fill-up, or ambient temperature differences seem to affect mpg. Good luck.
 
1 - 3 of 3 Posts
Top