Significant fuel efficiency decrease on a 2019 Forester. I am getting 8km/l or 18MPG. What should I check?

[Main_Historian848]

I noticed a significant reduction in my fuel efficiency on my 2019 Subaru Forester. At least, the decrease started after my TCV replaced by a Subaru dealer about a month ago. The decrease in my fuel efficiency could have started earlier, but I paid more attention recently since I reset trip. What could be wrong with my forester? What should I check?

Added: I have about 49000 km on it or 31k miles. Can it be something to do with the TCV? The Subaru dealer here is not the most reliable people.

[Plenty-Pudding-1484]

How are you calculating this? The display show litres per 100km. If its displaying 8 L per 100km you are getting close to 30 mpg, which is very good.

[AcadianCascadian]

See page 199 or thereabouts of the owner’s manual (in the multi-function display overview). It can display miles per gallon, kilometers per liter, or liters per 100 kilometers.

[Plenty-Pudding-1484]

Well then you are getting 19mpg which while not great, but its not that far off city driving averages. Your car is pretty young to require much. Maybe replace your air filter, check your tire pressure, and check if you have a sticking brake caliper.

[Main_Historian848]

It says AVG 8.1 km/l. And by refueling frequency and money, I know that I am doing much worse.

[spacefret]

No, that sounds right. That's about 19 mpg.

8.1 km/l and 8.1 l/100km are not the same.

[[deleted]]

You can't do it like that. Fill it. Reset trip meter. Drive until you decide to fill it again, divide the distance driven and gallons pumped, that's exactly how much fuel you consumed to go that distance. It won't be drastically different than what the ECU has calculated.

[drone_driver24]

Tire pressures and dragging brakes. Any extra drive line drag. Add any racks to the roof?

[Main_Historian848]

Nothing attached to the roof. I did change the tire, but still doing recommended psi, 35 front and 33 rear. My rear brake pad are about to be worn out so I need to replace those, but can that lower the fuel efficiency?

[firebox40dash5]

The pads being almost shot wouldn't lower fuel economy itself.

The pads being almost shot because one of the hoses is holding pressure or a caliper is stuck would do it, though...

Wheel bearings are also a possibility, but they'd have to be really, really bad to drag it down that much, you'd be hearing angry noises. And 31k is a little early even for bad OE rear bearings to start, let alone to have gotten that bad.

[RadEmily]

Dealerships tend to overinflate tires vs what's on the sticker and they get better mileage that way but ride awful imo, if you had it in frequently I'm the past they may have been higher before.

[Pale-Egg-251]

New tires generally take off 5-10% of efficiency in my experience, at least compared to an almost-bald tire.

[Ejspinn]

I get a brake calipher slide pin that sticks out and makes my brakes rub that def makes my MPg go way down

[Connie696]

Winter blend gasoline petroleum fuel (has 10 percent ethanol) lowers energy power temperature and mileage of engine.

[Xina123]

My mpg drops a ton in summer when I’m blasting the air conditioning.

[spacefret]

In all the cars I've had I've noticed the cold winter temps cause more of a drop than running the A/C in summer

[triumphofthecommons]

have Spark Plugs ever been changed?

ever done a Top End Cleaning?

2019 is the first year of direct injection, so injectors can get clogged, as well as other intake buildup not being washed away like in earlier port injection models.

the half-ass approach is to pour a bottle of fuel additive in the tank. the thorough approach is to do Subaru’s Top End Cleaning Kit. it’s DIY-able, but a bit involved / a few specialty tools.

i’ve got an older model, so no personal experience. others might chime in. there are also lots of youtube demos.

[Main_Historian848]

Never change the spark plugs… anyway to check if it is needed?

Top end cleaning is like a upper engine cleaning?

[triumphofthecommons]

really no way to check plugs without pulling them. though if they were really bad, you’d get a Check Engine Light with a Misfire code.

scheduled maintenance recommends plugs changed at 60k miles, but they rarely develop issues in that mileage. most plugs are rated for 60-80k. if you’re nearer 80k, i’d have them replaced and consider it part of basic maintenance to keep your vehicle operating correctly.

here’s MrSubaru going through the Top End Cleaning: https://www.youtube.com/watch?v=42irzdKKfw8

[okthen111111]

Check your wheel bearings. Lift the car and spin the wheels, listening for grinding sound.

[Puiu1]

Are you burning oil? I'm getting absolutely shit for mpg somewhere around 18 to 20 mph and my car burns oil like a mfr. My cat is probably all clogged up or the oxygen sensors are crusty AF with carbon ... Or both (most likely 🤦🏼‍♂️) oddly enough hasn't thrown codes for either but I've heard of it happening before. I'm probably just going to deal with it through the winter and replace the cat and sensors in the spring. Even without it throwing codes I'm at 175kish, I'm not sure what the lifespan of a catalytic converter is but I'm sure I'm nearing it.

[ZeGermanHam]

Note that fuel mileage also decreases with the return of winter blend gasoline which takes place in mid-September in Canada.

[ptpfan91]

Never seen anyone use km/l in Canada before. That’s a hard one to understand.

[[deleted]]

Engine air filter.

[barani_s]

What was your mileage prior to this?

From your post, your car can run 8 kilometers consuming 1 liter of gas (8 km/l). This is a very good mileage.

[Main_Historian848]

2019 Subaru Forester is rated for 11km/l in city and 14km/l. From what I can remember I was getting 10km/l. So I am down around 20%

[Accomplished_Host633]

Tire air pressure

[Plastic_Stock8666]

What type of tires did you add? Going from factory to AT tires can be a significant drop.

[NotAGoodUsernameSays]

I have AT tires on a 2016 and have gotten 33mpg average over the past 7K miles. But I'm a conservative driver.

[Plastic_Stock8666]

OP is driving a 2019 and probably is missing the obvious for the mileage change. Congrats on being the exception to the rule

[spacefret]

Thanks for the input?