What is affecting my fuel consumption?

[DrNick]

Over that last few months I've seen my fuel consumption fall from 33-34mpg to 28-30mpg. (W210 300TD Est)

I drive very consistently and do the same route every day, which is motorway on cruise control.

There is no loss of urge from the engine and it pulls cleanly towards the red. There is no smoke visible.
Tyres are pumped up and wear looks OK. (I've had all 4 tyres changed recently and this made no difference)
No signs of puddles of diesel under the car.
New air filter

Running Millers through it makes no difference. It may even be that the fall off coincided witht he first additrion of Millers. Stopping adding the Millers hasn't made any difference.

Anyone got any ideas?

 

[Brian WH]

Over that last few months I've seen my fuel consumption fall from 33-34mpg to 28-30mpg. (W210 300TD Est)

I drive very consistently and do the same route every day, which is motorway on cruise control.

There is no loss of urge from the engine and it pulls cleanly towards the red. There is no smoke visible.
Tyres are pumped up and wear looks OK. (I've had all 4 tyres changed recently and this made no difference)
No signs of puddles of diesel under the car.
New air filter

Running Millers through it makes no difference. It may even be that the fall off coincided witht he first additrion of Millers. Stopping adding the Millers hasn't made any difference.

Anyone got any ideas?

Is it due a service??

 

[DrNick]

Technically yes in a thousand miles, but given that its tyres are pumped up, and its got a new air filter and its had injector cleaner through, its really only in need of an oil change, oil filter, fuel filter and a good look over.

Is there anything specific you are getting at?

 

[Brian WH]

Technically yes in a thousand miles, but given that its tyres are pumped up, and its got a new air filter and its had injector cleaner through, its really only in need of an oil change, oil filter, fuel filter and a good look over.

Is there anything specific you are getting at?

The fuel filter may be significant and if partly blocked could give you bad mpg, but would also affect the acceleration etc. Sometimes these affects are marginal and not noticed until the are fixed and you see the sudden improvement!! Injectors may be clean but if worn would give worse mpg.

The other thought is the cold weather? When cold the car will take longer to warm up and affect the mpg. See if the Spring weather helps.

 

[DrNick]

Any idea how many fuel filters are on this car? I know about the one at the front, but I heard rumours about a pre-filter. There is a small in line filter near the brake servo - any idea what this is?