[mfbeamerboy]

Drive an F32 420i 6mt. Posted about this before but now I’m certain something’s up.

It ain’t the tyres cos I’ve just swapped them for brand new non run flat Goodyear asymmetric 6s. OMG the ride is like butter by the way. £230 a corner for the prior Bridgestone potenzas - load of crap.

Anyway tyres are 38 psi up front and 33 rear. Factory spec.

My mum just filled her 220i active tourer - ZF8 gearbox - and doing 40mph down a dual carriageway she got 50 MPG!!! I’m staring at the consumption and every move she does I know mine would be 50% lower. It’s insanely higher yet the same engine.

I have full engine oil, high spec Castrol. Fully replaced coolant and lines. Brand new tyres.

The only things I can think of are the gearbox and the drivetrain losses (hers being FWD). But in no planet does that cause my fuel consumption to be nearly half hers.

I get 33mpg driving like a granny.

What the hell is causing this?

[mfbeamerboy]

Would an OBD reading tell me if I need new spark plugs or coil packs?

I’ve also cleaned the engine air filter, which looked brand new anyways.

I can’t think of anything else.

[Wires]

Are you sure you have the tire spec correct? It's usually higher in the rear than front.

As for your mum's mileage, how is that being measured? I doubt any BMW that doesn't have electric assist reaches 50MPG unless it's downhill with a tailwind. If you are using what the dash is saying, reset it and try again. It might be out of wack and giving false MPG.

[mfbeamerboy]

Originally Posted by Wires

Are you sure you have the tire spec correct? It's usually higher in the rear than front.

As for your mum's mileage, how is that being measured? I doubt any BMW that doesn't have electric assist reaches 50MPG unless it's downhill with a tailwind. If you are using what the dash is saying, reset it and try again. It might be out of wack and giving false MPG.

It was downhill. But right after a fuel fill up, I know how my car behaves in terms of MPG leaving that fuel station and joining that carriageway, and it was definitely using a lot less fuel than mine was.

I my have the PSIs other way around, all I know is they’re to spec.

Any ideas?

[Tommy D]

The proper way to measure fuel economy is how many miles you drive per tankful, not realtime looking at the gauges on the dash. I'm sure when you measure that way, your Mum's car will be within a few MPG's

[Wires]

^what he said. The dash will give "decent" longer term steady state averages. The car filters out hard acceleration, and will give you a much better MPG on the dash than reality.

[mfbeamerboy]

Originally Posted by Wires

^what he said. The dash will give "decent" longer term steady state averages. The car filters out hard acceleration, and will give you a much better MPG on the dash than reality.

^^
I get maximum 430 miles out of a tank. That’s me driving in a manner not conducive to a bimmer. That’s what 430s, 440s should achieve with my style of driving.

I KNOW something is wrong. I’m feathering the pedal, barely braking, and using cruise control, in highest possible gears ( I aim to cruise around 1k rpm).

[agentorange]

I see your location is London. Are you getting 33 mpg with a lot of stop-start traffic? If so, I don't think you are doing so bad.

Try this. Reset the trip and take a run on one of the motorways out of London at a quiet time. Run it at the speed limit on the cruise control as much as you can. You should see something like 40 mpg on a 100 mile round trip. If you don't, my only thoughts are binding brakes, a fuel leak, or a diff about to seize.

[Wires]

According to multiple Google sites, 33 MPG is "real world MPG" :
https://www.honestjohn.co.uk/realmpg...ries-2013/420i

[Billfitz]

Even 33 MPG is high depending on your driving conditions. I average 23 MPG with 75% of my driving at speeds of 40 MPH or less. Cruising at 75 MPH on flat terrain I get 40 MPG.

[mfbeamerboy]

Originally Posted by Billfitz

Even 33 MPG is high depending on your driving conditions. I average 23 MPG with 75% of my driving at speeds of 40 MPH or less. Cruising at 75 MPH on flat terrain I get 40 MPG.

My parents long term average in their 220i active tourer is 38! And they drive in between sensibly and spiritedly.

[mfbeamerboy]

Originally Posted by Wires

According to multiple Google sites, 33 MPG is "real world MPG" :
https://www.honestjohn.co.uk/realmpg/bmw/4-series-2013/420i

I think I’m overthinking it because I’m averaging the average cost of ownership per year and the fuel is making that increase a lot. However I’d have been paying that in my old car, just not as much. I’m doing a good amount miles too. Maybe I’m just using it too much and being to harsh with my £ numbers.

Insurance was v high. And they depreciate fast and hard in uk.

However I am shocked that the same engine in a less aerodynamic car is driving 20% -35% more efficiently than mine.

I can’t believe it’s down to the RWD-train loss or the manual gearbox, I’m thinking it’s something with the car.

How much of an affect would alignment have if off? It goes straight with wheel dead centre.

[agentorange]

If I'm reading the specs for the 220i Active Tourer correctly, it uses a 3-cyclinder engine 1.5 litre with hybrid backup. The BMW UK page shows a 420i uses a 4-cyclinder with no hybrid gadgetry. You are not comparing like with like. The aerodynamic differences may not be as big as you think. It's more likely that the smaller, 3-cylinder engine is particularly efficient when cruising.

[Billfitz]

"Engine: The 220i has a 1.5-liter turbocharged 3-cylinder engine with 156 horsepower, plus a mild hybrid system that boosts the output to 170 horsepower."

Yep. That explains a lot. And there's this: "The curb weight of a BMW 420i varies by model and can range from 1,680 kg to 1,835 kg. The BMW 2 Series Active Tourer has an unladen weight of 1,435–1,465 kg."

As usual the bitch lies in the details.

[mfbeamerboy]

Originally Posted by Billfitz

"Engine: The 220i has a 1.5-liter turbocharged 3-cylinder engine with 156 horsepower, plus a mild hybrid system that boosts the output to 170 horsepower."

Yep. That explains a lot. And there's this: "The curb weight of a BMW 420i varies by model and can range from 1,680 kg to 1,835 kg. The BMW 2 Series Active Tourer has an unladen weight of 1,435–1,465 kg."

As usual the bitch lies in the details.

The 220i active tourer doesn’t have a 3 cylinder 1.5L. That would be the x18i variants, of which I believe weren’t even sold for their cars model year (2019). Like all other x20i BMWs of the modern era, it’s the 180(ish) HP 300nm 2 litre turbo.

The weight thing is surprising to me. That car, to me, looks like a smaller SUV. My car is a sports car half its height, plus a lot more aerodynamic (looks it anyways).

So the only actual difference here is a few hundred kilos of weight.

Okay cool.

So why are there people on here with 430is claiming 38mpg mixed? And the only way I’m touching 40 is on a long boring motorway drive - which BMW reckons should get 50+?

[mfbeamerboy]

Originally Posted by agentorange

If I'm reading the specs for the 220i Active Tourer correctly, it uses a 3-cyclinder engine 1.5 litre with hybrid backup. The BMW UK page shows a 420i uses a 4-cyclinder with no hybrid gadgetry. You are not comparing like with like. The aerodynamic differences may not be as big as you think. It's more likely that the smaller, 3-cylinder engine is particularly efficient when cruising.

You might be talking about that new ugly bastard they’ve released. My parents car is a 2019 220i and is most definitely a 4 cylinder with the same engine as all over x20is, with no hybrid technology. Mine is a 2018 420i.
Also I’m pretty sure all the new bimmers have mild hybrid batteries?

[agentorange]

Originally Posted by mfbeamerboy

You might be talking about that new ugly bastard they’ve released. My parents car is a 2019 220i and is most definitely a 4 cylinder with the same engine as all over x20is, with no hybrid technology. Mine is a 2018 420i.
Also I’m pretty sure all the new bimmers have mild hybrid batteries?

OK, that levels the playing field somewhat. The Active Tourer has about 10% more frontal area, and I would guess with modern CFD techniques that the drag coefficients are similar.

Does your parents' car use the Aisan 8-speed transmission, or the 7-speed DCT? I'm having trouble finding out which Active Tourers have the DCT box.

One more thing to consider on your car. Is the torque converter lockup working? Lockup failure will kill fuel mileage.

[mfbeamerboy]

Originally Posted by agentorange

OK, that levels the playing field somewhat. The Active Tourer has about 10% more frontal area, and I would guess with modern CFD techniques that the drag coefficients are similar.

Does your parents' car use the Aisan 8-speed transmission, or the 7-speed DCT? I'm having trouble finding out which Active Tourers have the DCT box.

One more thing to consider on your car. Is the torque converter lockup working? Lockup failure will kill fuel mileage.

Out of interest what’s a CFD technique?

It’s the ZF8 gearbox mate, I thought the DCTs were only used in full fat M models?

Torque converter lockup - how would I know if it’s working?

[agentorange]

Originally Posted by mfbeamerboy

Out of interest what’s a CFD technique?

It’s the ZF8 gearbox mate, I thought the DCTs were only used in full fat M models?

Torque converter lockup - how would I know if it’s working?

Computational Fluid Dynamics, CFD, how you design the best shape for minimum drag on a computer. It's all the rage in car, aircraft, and ship design.

I asked about the DCT because the Interwebz were a bit vague on the subject.

Just read your original post again, and realized you are driving a manual, so no torque converter.