Spark plug replacement - Fuel consumption?

[BlackC55]

My car pass MOT test every year with flying colors.
Readings from exhaust fumes are within tolerances

Thats a minimal emission test that will not show a lazy O2 sensor.
MOT's are not a certificate that your car is in good condition. The test is minimal standard, and believe me its very minimal.

 

[Deleted member 149005]

Enthusiasts cars won't be driven the way MB had their intentions per their recommendations.
These cars are driven on sunny days.
We can't follow their recommendations on gearbox oil changes or spark plug interval replacement.
It will be very costly if we follow MB service intervals and drive very little per year.

When it comes to annual A - B service, I do this every 2 years at a specialist.
For engine oil and filter changes, I do this every year.

see post 9 - not loosening them at the very least could cost you a lot more

 

[Deleted member 149005]

Don't rely on the fuel gauge to guess your fuel consumption

The only way to measure it is to fill the tank, drive to until at least 1/2 tank used, refill the tank and calculate the consumption

 

[noogieman]

Don't rely on the fuel gauge to guess your fuel consumption

The only way to measure it is to fill the tank, drive to until at least 1/2 tank used, refill the tank and calculate the consumption

Will try this when my needle touch 1/2 of the tank then refill.
I'll compare the litres filled up vs km's registered on my speedo.

Thanks

 

[noogieman]

Thats a minimal emission test that will not show a lazy O2 sensor.
MOT's are not a certificate that your car is in good condition. The test is minimal standard, and believe me its very minimal.

MOT test is a government test facility.
If cars are not safe or road worthy or have faults in emissions tests, cars will fail the test and banned from driving on public roads.
Owners has to take the car in for repair to make it OK again and make a new MOT test getting approved.

 

[noogieman]

see post 9 - not loosening them at the very least could cost you a lot more

Never done this before!
Once plugs were fitted they stayed in their sockets for 11 years now.
I believe mechanics put copper paste on threads preventing rust issues or seizing?
Do they?

 

[Bellow]

The only difference I have ever noticed with new plugs is sharper throttle response - for half a mile.

Twin plug per cylinder is more sensitive though. If one plug goes down you wont get a mis-fire as the other plug will ignite the charge. The time taken to burn the mixture will be longer though due to the longer flame path with just one plug. This can lead to detonation. That will be countered by retarding the ignition timing (compounding the slow burn) and ultimately the heat remaining in the charge when the exhaust valve opens will give it a hard time. The exhaust valve is a detonation hot spot also so it becomes a vicious circle very quickly.

For this reason twin plug per cylinder motors need care with their ignition systems - especially HT leads.

 

[Will]

MOT test is a government test facility.
If cars are not safe or road worthy or have faults in emissions tests, cars will fail the test and banned from driving on public roads.
Owners has to take the car in for repair to make it OK again and make a new MOT test getting approved.

I think you’re getting confused.

These are analogue sensors, they can work without failing an emissions test but still not perform optimally.

As BlackC55 has said, most inspections/MOT tests are to meet a minimum standard, not a fine state of tune. A 20 year old lambda sensor which has had 100k miles worth of exhaust gases and heat cycles may not respond as accurately as a new one.

Whether the cost of replacement warrants the possible savings in fuel costs is another matter...

 

[szucchet]

Like others have posted i'd normally say they wouldn't affect fuel efficiency that much but would still be good to replace to ensure that the engine is running as efficiently as possible!

Aside from oil/filter changes, I tend to go with milage too for consumables like the spark plugs as I rarely drive the miles most people put their cars through each year!

 

[Petrol Pete]

Never done this before!
Once plugs were fitted they stayed in their sockets for 11 years now.
I believe mechanics put copper paste on threads preventing rust issues or seizing?
Do they?

Not always , and in fact many engine manufactures recommend NOT doing this. But they do recommend replacing the spark plugs both on mileage and/or time. my car has a M113 AMG engine and changing the spark plugs was one of the first things I had done when I bought it at around 120K miles because the service history shown it had only been done once and I had heard stories of plugs seized in by time (not mileage) which in some cases the engine had to be removed to get the plug(s) out.

My C55 is a daily driver and averages around 22 mpg. When I bought it improving the fuel consumption was the last thing on my mind. If I were you I would leave the fretting over the fuel consumption to the Diesel boys on here and just enjoy the feel of the M113 ...more

 

[noogieman]

I think you’re getting confused.

These are analogue sensors, they can work without failing an emissions test but still not perform optimally.

As BlackC55 has said, most inspections/MOT tests are to meet a minimum standard, not a fine state of tune. A 20 year old lambda sensor which has had 100k miles worth of exhaust gases and heat cycles may not respond as accurately as a new one.

Whether the cost of replacement warrants the possible savings in fuel costs is another matter...

I had my oxygen sensors replaced some years ago.
They are younger than 20 years.

My car had one of them (the total of 2x) oxygen sensors malfunctioning, not having the CEL in the cluster it's impossible to know when a component breaks?
The other oxygen sensor covered the readings for exhaust fumes for the faulty one and my car still passed annual emissions tests.
The only way to find out if an oxygen sensor is malfunctioning without having CEL lamp on cluster for 1997- 1999 cars is from erratic automatic gear changes between 1st and 2nd gear.
I took my car to the dealershite and they red the codes showing one oxygen sensor was bad.
It broke down long before the estimated 100,000 miles which Bosch claims they would last!
Parts seem to break down when you don't expect them to do?

When all components are in synergy and being synchronized for a healthy engine , then everything works as it should and is most effective on fuel consumption.
Replacing air/fuel filters on time.
Replacing ignition components on time.
Engine oil and filter on time.
Etc etc.

 

[Stratman]

A bit off topic but here goes. Light aircraft engines generally have two ignition systems for safety's sake, magnetos with fixed timing so no advance and retard mechanism to fail. It's also why they sound like a bag of spanners at idle as the timing is set for cruise revs, around 2200-2800 give or take. Anyway, to the point. One of the pre flight checks is 'mag drop'. Each magneto is switched off in turn to ensure the other one is working, and the RPM drop must be within limits, 250ish rpm was typical. The twin ignition system is therefore worth about 250 rpm in extra power at idle in a badly timed engine, and presumably more once it's at operating revs. As Bellow mentioned, two flame fronts makes the flame front and combustion chamber pressure peak sooner, resulting in a harder push on the piston crown.

 

[flowrider]

Will try this when my needle touch 1/2 of the tank then refill.
I'll compare the litres filled up vs km's registered on my speedo.

Thanks

You can use Fuelly to track mpg if you can be bothered to keep track, I started tracking for a while then got bored doing it.

 

[noogieman]

You can use Fuelly to track mpg if you can be bothered to keep track, I started tracking for a while then got bored doing it.

Is Fuelly a phone app?
Unfortunately I don't have such fancy things.

 

[flowrider]

Is Fuelly a phone app?
Unfortunately I don't have such fancy things.

Its is a phone app and website.

 

[noogieman]

Its is a phone app and website.

I'll look it up
Thanks

 

[markjay]

Never done this before!
Once plugs were fitted they stayed in their sockets for 11 years now.
I believe mechanics put copper paste on threads preventing rust issues or seizing?
Do they?

This is an interesting point.

For many years I used copper grease on spark plug threads (and before that, graphite grease). And you are right that a thread lubricated with copper grease won't seize. The same applies to wheel bolts.

Then things changed, we were told that spark plugs and wheel bolts should be fitted dry and tightened to torque. Which is fine.

But when I changed the factory-fitted spark plugs on my Vauxhall Omega 2.6 (15 years ago...), the threads were lubricated with copper grease from new. Which I wasn't expecting....

So the official advice is to fit the spark plugs dry and change them at the prescribed interval.

But my impression is that you won't go wrong with lubricating them with copper grease - as long as you apply the grease sparingly, on the threads only, and tighten the plug properly (you don't want a loose plug being fired out of its socket and into the bonnet).

 

[noogieman]

This is an interesting point.

For many years I used copper grease on spark plug threads (and before that, graphite grease). And you are right that a thread lubricated with copper grease won't seize. The same applies to wheel bolts.

Then things changed, we were told that spark plugs and wheel bolts should be fitted dry and tightened to torque. Which is fine.

But when I changed the factory-fitted spark plugs on my Vauxhall Omega 2.6 (15 years ago...), the threads were lubricated with copper grease from new. Which I wasn't expecting....

So the official advice is to fit the spark plugs dry and change them at the prescribed interval.

But my impression is that you won't go wrong with lubricating them with copper grease - as long as you apply the grease sparingly, on the threads only, and tighten the plug properly (you don't want a loose plug being fired out of its socket and into the bonnet).

I spoke with the mechanic.
He told me plugs were tight when he tried to remove them but he managed without problems.
They were in there for approx 11 years and never removed nor refit.
I asked mechanic about greasing the threads, he always put a very little grease just for safety preventing seize.

The mechanic had to replace one of the plug wires as it was a little corroded inside the hat.
He replaced it with genuine MB part.

Mechanic told me plugs were worn in a healthy way, the way they should wear during it's lifespan of use, plugs were not oily or tainted.
Meaning my car has functioned the way it should.

I never had any issues with my car before replacing my plugs.
I think 11 years was a long time overdue, regardless of mileage on the old plugs which was approx 35000km.

 

[Petrol Pete]

I certainly hope your mechanic is not putting 'grease' on the threads of your new spark plugs. I trust you mean an anti-seize product ?

 

[190]

A bit off topic but here goes. Light aircraft engines generally have two ignition systems for safety's sake, magnetos with fixed timing so no advance and retard mechanism to fail. It's also why they sound like a bag of spanners at idle as the timing is set for cruise revs, around 2200-2800 give or take. Anyway, to the point. One of the pre flight checks is 'mag drop'. Each magneto is switched off in turn to ensure the other one is working, and the RPM drop must be within limits, 250ish rpm was typical. The twin ignition system is therefore worth about 250 rpm in extra power at idle in a badly timed engine, and presumably more once it's at operating revs. As Bellow mentioned, two flame fronts makes the flame front and combustion chamber pressure peak sooner, resulting in a harder push on the piston crown.

Dual plugging is a common modification on old BMW flat twins. One of the outcomes is up to 6 deg less ignition advance is needed because of the shorter flame path. Some improvement in efficiency seems to me inevitable as the piston is not being opposed by the pressure rise for as long. The maximum ignition advance figure is considered a sort of tell tale of good combustion chamber design with poor designs need more advance and good designs needing less.