Air filter,petrol engine,normally aspirated | Motoring discussion | Back Room Forum

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Sat 7 Dec 2013 13:55

Air filter,petrol engine,normally aspirated - brum

Am I right in thinking that because lambda probes ( indirectly) control petrol/air mixtures, that changing an air filter won't affect fuel consumption, and the state of the air filter only effects the maximum power/torque available? I'm asking as I'm considering changing one before its service interval as the car in question is using a bit more fuel than normal. I appreciate that winter petrol has a negative effect on economy.

Edited by brum on 07/12/2013 at 13:58

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Sat 7 Dec 2013 14:43

Air filter,petrol engine,normally aspirated - oldroverboy.

I appreciate that winter petrol has a negative effect on economy.

Petrol is the same, your car takes a bit longer to warm up. first take out the air filter and clean it with an air hose, if it was changed within the last year i doubt if it would make a lot of difference anyway. and unless it is a very very very cheap air filter the cost savings might not be worth it, don't forget, lots of short runs in winter mean even poorer mileage.

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Sat 7 Dec 2013 15:11

Air filter,petrol engine,normally aspirated - RT

Winter has a triple whammy on fuel consumption - takes longer to warm up using more fuel in the process - fewer longer distance days out - more short runs "because it's raining".

Examine the existing air filter - if it's dirty before the service is due it may be that you've got excessive crankcase ventilation fumes going through - could be engine wear, wrong oil or crankcase ventilation fault.

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Sat 14 Dec 2013 19:13

Air filter,petrol engine,normally aspirated - SteveLee

Winter has a triple whammy on fuel consumption - takes longer to warm up using more fuel in the process - fewer longer distance days out - more short runs "because it's raining".

Examine the existing air filter - if it's dirty before the service is due it may be that you've got excessive crankcase ventilation fumes going through - could be engine wear, wrong oil or crankcase ventilation fault.

Increased air density from the lower air temperature also increases fuel consumption as you require more fuel to match the increased volume of air.

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Sat 14 Dec 2013 19:39

Air filter,petrol engine,normally aspirated - RT

Increased air density from the lower air temperature also increases fuel consumption as you require more fuel to match the increased volume of air.

Not on a fuel injected engine - more air density does mean more oxygen so more fuel but it also increases power so the throttle opening can be less!

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Mon 16 Dec 2013 01:26

Air filter,petrol engine,normally aspirated - SteveLee

Increased air density from the lower air temperature also increases fuel consumption as you require more fuel to match the increased volume of air.

Not on a fuel injected engine - more air density does mean more oxygen so more fuel but it also increases power so the throttle opening can be less!

Only if there was a perfect feedback system ensuring a linear and repeatable acceleration curve - hence the "can" be less, drivers tend to just drive and plonk the old throttle down the same amount, the car will just accelerate harder in cold conditions burning more fuel.

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Sat 7 Dec 2013 15:40

Air filter,petrol engine,normally aspirated - craig-pd130

An air filter has to be REALLY clogged before it will impact on fuel economy or performance, it's usually the least restrictive part of the intake system.

Although I do remember someone posting on SeatCupra.net about how their car's power had dropped right off. When he looked in the airbox, a section of plastic carrier bag had been sucked in and got stuck over some of the air filter area ...

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Sat 7 Dec 2013 17:25

Air filter,petrol engine,normally aspirated - DrippingSump

A clean air filter is important - no doubts there. However an engine will take a lot of blockage before it actually chokes to death.

I recall from my days as a sevice manager in a John Deere dealership in a dusty part of the world a farmer called out the mobile service because the tractor was feeling a bit sad and was taking some effort to start and it would not pull the skin off a rice pud.

I saw the air filter when it came back to the workshop and it looked like a log of wood it was so clogged. It was solid. It was quite remarkable.

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Sat 7 Dec 2013 18:13

Air filter,petrol engine,normally aspirated - brum

Sorry, but no-one's answered my question. Rephrased - do lambda probes ensure stiochiometric combustion regardless of air filter condition? Or do they only trim the fuel/air ratio under certain conditions , e.g idling, or steady state running.

Winter petrol does not only exist but is a legal obligation as is winter diesel. Delivered between Nov and Mar. It has a different formulation with slighty lower calorific value and has a different vapour pressure v temperature spec. to stop it freezing in carb jets and injector nozzles.

Edited by brum on 07/12/2013 at 18:26

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Sat 7 Dec 2013 18:37

Air filter,petrol engine,normally aspirated - Collos25

Who told you that?

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Sat 7 Dec 2013 18:53

Air filter,petrol engine,normally aspirated - brum

BS EN 228:2008 and also UK government regulations.

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Sat 7 Dec 2013 19:17

Air filter,petrol engine,normally aspirated - brum

The Motor Fuel (Composition and Content) Regulations 1999 and subsequent amendments and the EU standards they refer to.

Must admit I was surprised when I found about this last year, thinking only diesel had a winter formulation.

Edited by brum on 07/12/2013 at 19:21

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Sat 7 Dec 2013 18:53

Air filter,petrol engine,normally aspirated - craig-pd130

Sorry, but no-one's answered my question. Rephrased - do lambda probes ensure stiochiometric combustion regardless of air filter condition? Or do they only trim the fuel/air ratio under certain conditions , e.g idling, or steady state running.

Yes, in most petrol cars made since the introduction of catalysts, they should run "closed loop" - in other words, the ECU will always be adjusting the mixture to ensure that combustion stays as close to stoichiometric as possible. In some cases the ECU might allow 'open loop' running -- for example under full throttle acceleration -- but the rest of the time the mixture should be controlled.

So you're correct - if there's an intake restriction (blocked filter / intake snorkel) then the ECU should adjust mixture accordingly.

Edited by craig-pd130 on 07/12/2013 at 18:55

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Sat 7 Dec 2013 18:56

Air filter,petrol engine,normally aspirated - brum

Thanks, what I thought. Changing a slightly (or even moderately) dirty filter should make little difference then. (Unless you have a heavy foot)

It's logical, since the catalytic converter needs a controlled exhaust otherwise it would not function.

Edited by brum on 07/12/2013 at 19:04

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Sat 7 Dec 2013 19:42

Air filter,petrol engine,normally aspirated - RT

Sorry, but no-one's answered my question. Rephrased - do lambda probes ensure stiochiometric combustion regardless of air filter condition? Or do they only trim the fuel/air ratio under certain conditions , e.g idling, or steady state running.

Winter petrol does not only exist but is a legal obligation as is winter diesel. Delivered between Nov and Mar. It has a different formulation with slighty lower calorific value and has a different vapour pressure v temperature spec. to stop it freezing in carb jets and injector nozzles.

Yes - the MAF or MAP plus the lambda sensor will keep the mixture correct on an engine with closed-loop fuel injection - but only within a band either side of normal - outside that band it'll go into preset limp mode.

The USA has a winter gasoline specification but I can find no reference for one in Europe.

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Sat 7 Dec 2013 20:15

Air filter,petrol engine,normally aspirated - brum

The USA has a winter gasoline specification but I can find no reference for one in Europe.

Every fuel company has specs like this: www.highlandfuels.co.uk/downloads/ProdSpecSulphurF...f

I referred to the UK/EU regulations/legislation earlier

Edited by brum on 07/12/2013 at 20:18

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Sat 7 Dec 2013 20:23

Air filter,petrol engine,normally aspirated - bathtub tom

I understand a blocked air filter doesn't affect fuel injected cars like it did carbureted ones (where it had the effect of making them run rich). Although restricting the air intake would, I assume, limit power.

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Sat 7 Dec 2013 21:11

Air filter,petrol engine,normally aspirated - RT

The USA has a winter gasoline specification but I can find no reference for one in Europe.

Every fuel company has specs like this: www.highlandfuels.co.uk/downloads/ProdSpecSulphurF...f

I referred to the UK/EU regulations/legislation earlier

No difference in octane values and no reference to calorific values - basically just different evaporation rates to avoid losses in summer.

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Sat 7 Dec 2013 22:08

Air filter,petrol engine,normally aspirated - galileo

Winter petrol does not only exist but is a legal obligation as is winter diesel. Delivered between Nov and Mar. It has a different formulation with slighty lower calorific value and has a different vapour pressure v temperature spec. to stop it freezing in carb jets and injector nozzles.

Being pedantic, petrol itself does not freeze, typical freezing point of iso-octane, for example, is -107 degrees C. Moisture in petrol could freeze, humid air can lead to icing in carburettors in cold weather, piston engined aircraft had heaters on intakes to prevent this.

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Sat 7 Dec 2013 23:10

Air filter,petrol engine,normally aspirated - brum

Being pedantic, petrol itself does not freeze, typical freezing point of iso-octane, for example, is -107 degrees C. Moisture in petrol could freeze, humid air can lead to icing in carburettors in cold weather, piston engined aircraft had heaters on intakes to prevent this.

Thanks, I stand corrected.

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Sun 8 Dec 2013 06:13

Air filter,petrol engine,normally aspirated - RT

In carburettors, there's also a pressure differential through the venturi which reduces the temperature so that icing can occur even at above zero temperatures.

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Sat 14 Dec 2013 18:35

Air filter,petrol engine,normally aspirated - John F

A clean air filter is important - no doubts there. However an engine will take a lot of blockage before it actually chokes to death.........

...... saw the tractor air filter when it came back to the workshop and it looked like a log of wood it was so clogged. It was solid.

Ha ha - just as I found in my Honda engined sluggish lawn mower - I suspect the previous owner thought it had to be soaked in oil like the old 'brillo pad' ones! Had to wash it in petrol, then Fairy liquid.....

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Sat 14 Dec 2013 18:30

Air filter,petrol engine,normally aspirated - John F

I'm asking as I'm considering changing one before its service interval as the car in question is using a bit more fuel than normal. I appreciate that winter petrol has a negative effect on economy.

I have never changed an air filter in my life. This 'requirement' is another example of unnecessary polluting maintenance and waste of money, rewarding only the garage owners. In this relatively dust-free country they don't clog up. Every 20 or 30,000 miles I remove it and brush between the external folds with a paintbrush, then give it a good blast with a hair drier. The modern flat paper ones open up like a concertina revealing not much more than a few bits of dried leaf and bugs.

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Sat 14 Dec 2013 19:18

Air filter,petrol engine,normally aspirated - SteveLee

An aftermarket air filter costs £6-10 for most cars and five minutes to change - it's hardly a great conspiracy to rob the motorist!

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Sun 15 Dec 2013 15:34

Air filter,petrol engine,normally aspirated - John F

An aftermarket air filter costs £6-10 for most cars and five minutes to change - it's hardly a great conspiracy to rob the motorist!

True, but all these little things [annual oil and filter change no matter what the mileage, coolant change, brake fluid change after a very few yrs, new valves every tyre change] add up.

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Mon 16 Dec 2013 09:16

Air filter,petrol engine,normally aspirated - skidpan

True, but all these little things [annual oil and filter change no matter what the mileage, coolant change, brake fluid change after a very few yrs, new valves every tyre change] add up.

True but its all part of car ownership and maintenance of your investment. If you are happy not maintaining your car fair enough but I do not think you should be preaching this doctorine of non maintenance to others.

Not replacing brake fluid and tyre valves is just plain crazy, its costs a few pounds to do both and the consequences to yourself (and others probably) when you have a failure are unthinkable.

IMHO if you are not prepared top maintain your car correctly you should sell it instead of risking the safety of other road users.

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Mon 16 Dec 2013 23:00

Air filter,petrol engine,normally aspirated - John F

Not replacing brake fluid and tyre valves is just plain crazy, its costs a few pounds to do both and the consequences to yourself (and others probably) when you have a failure are unthinkable.

IMHO if you are not prepared top maintain your car correctly you should sell it instead of risking the safety of other road users.

Ho ho ho! Got to laugh at the absurdity of this criticism!

In nearly 50 yrs of driving the only brake failure I have ever experienced was a corroded pipe giving way in an ancient Ford Anglia. I have had the occasional puncture but tyre valve failure is almost unheard of. However, you will be pleased to know that I renewed them when I changed the 23yr old tyres on my 33yr old TR7 [which has passed its MoT examination every year since 1983]. I do sometimes wonder what examinations my critics have passed.

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Mon 16 Dec 2013 09:21

Air filter,petrol engine,normally aspirated - RT

An aftermarket air filter costs £6-10 for most cars and five minutes to change - it's hardly a great conspiracy to rob the motorist!

True, but all these little things [annual oil and filter change no matter what the mileage, coolant change, brake fluid change after a very few yrs, new valves every tyre change] add up.

Use the car less - the saving in fuel cost is enormous - and it stops the grabbing government getting their hands on your cash through the fuel duty and VAT.

With the money you save you could afford to have the car serviced!

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Mon 16 Dec 2013 09:32

Air filter,petrol engine,normally aspirated - gordonbennet

''Use the car less - the saving in fuel cost is enormous - and it stops the grabbing government getting their hands on your cash through the fuel duty and VAT.''

You can be a pay-less-to-government-waste-dept dissident by going LPG, far less tax paid....brings a smile to my face every time i fill up.

One of the many faced dick turpins will eventually hammer LPG too, with a bit of luck i'll have retired by then (unless the goal posts elasticate further) and, assuming haven't kicked the bucket, it'll be a bike/bus or a plug in hybrid, much will depend on road pricing and the surveillance state spy machine whether i run a car at all.

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Sat 14 Dec 2013 21:10

Air filter,petrol engine,normally aspirated - focussed

It's not only dust that blocks air filters. If a vehicle is used for a lot of winter driving, particularly motorways, the road salt spray will block an air filter quite effectively because the wet salt spray mist drawn in by the induction air gets trapped in the filter and dries out in the filter from the heat of the engine when it is stopped. Repeat a few hundred times and you've got a filter that is past it's best.

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Sun 15 Dec 2013 15:40

Air filter,petrol engine,normally aspirated - John F

It's not only dust that blocks air filters. If a vehicle is used for a lot of winter driving, particularly motorways, the road salt spray will block an air filter quite effectively because the wet salt spray mist drawn in by the induction air gets trapped in the filter and dries out in the filter from the heat of the engine when it is stopped. Repeat a few hundred times and you've got a filter that is past it's best.

Interesting - never thought of that. Not sure I believe it would provide significant impedance to airflow. Tongue test next May? Should be instant salty taste if significant deposits.

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Mon 16 Dec 2013 01:27

Air filter,petrol engine,normally aspirated - SteveLee

Most filters are paper - surely this rots over time?

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Mon 16 Dec 2013 11:57

Air filter,petrol engine,normally aspirated - John F

Most filters are paper - surely this rots over time?

Only if damp. I have some books >100yrs old. Many will have ancient newspapers in their lofts.

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Sun 15 Dec 2013 14:13

Air filter,petrol engine,normally aspirated - madf

Man knows more than all automotive engineers in thw world.. and says their service schedules are a waste of time and money.

Sorry I know whose advice I will follow.

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Sun 15 Dec 2013 23:42

Air filter,petrol engine,normally aspirated - brum

Man knows more than all automotive engineers in thw world.. and says their service schedules are a waste of time and money.

Sorry I know whose advice I will follow.

Thanks for your insult again, its like listening to a broken record...

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Mon 16 Dec 2013 00:31

Air filter,petrol engine,normally aspirated - Avant

Keep it civilised, please.

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Mon 16 Dec 2013 15:56

Air filter,petrol engine,normally aspirated - hillman

I once had a Ford Prefect of the side valve sit-up-and-beg type. The engine was worn, as was almost everything else about the car. The crank case breather was a pipe venting to atmosphere and the fumes coming from it were getting into the car. I drilled the air cleaner, 'brillo' type and added a spigot made of a short piece of electrical conduit then joined the crankcase breather to the spigot with a length of heater hose from my Cresta. Problem solved - GM assists Ford.

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Tue 17 Dec 2013 07:39

Air filter,petrol engine,normally aspirated - skidpan

Ho ho ho! Got to laugh at the absurdity of this criticism! In nearly 50 yrs of driving the only brake failure I have ever experienced was a corroded pipe giving way in an ancient Ford Anglia. I have had the occasional puncture but tyre valve failure is almost unheard of. However, you will be pleased to know that I renewed them when I changed the 23yr old tyres on my 33yr old TR7 [which has passed its MoT examination every year since 1983]. I do sometimes wonder what examinations my critics have passed.

Thanks JohnF for finding my criticism of your maintenance methods absurd.

However, running on the road on 23 year old tyres is just plain stupid. If one had exploded and caused a fatal accident you would not ahve been on here saying "well, nearly got another year out of them".

However it mayybe you are just one of those posters who come on a forum to get a reaction to their totally irresposible posts.

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Tue 17 Dec 2013 09:46

Air filter,petrol engine,normally aspirated - madf

However it mayybe you are just one of those posters who come on a forum to get a reaction to their totally irresposible posts.

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Tue 17 Dec 2013 19:31

Air filter,petrol engine,normally aspirated - Avant

This thread has run its course, and I hope Brum feels that his original question has been answered. Note Hillman's helpful post a few up from here which is still relevant.

Read-only.

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