e300 td - fuel/economy update

[mojo7676]

Just thought i'd post some info re poor fuel economy. the car is a 1998 e300td elegance, estate. bought about a few weeks ago, some service history with mercedes and seems in fairly decent condition. i'll cut to the chase...
v poor fuel economy- between 20-25 mpg, very steady driving. changed oil, air filter, oil filter and fuel filter and hoped for improvements. shoved in a load of redex and still no real joy. noticed slight wetness under one of nylon fuel pipes so after several/many communications from parrot of doom, changed the nylon fuel pipes on top of fuel pump (about 6 in all, i think). no improvement and still a leak/drip. Then changed small o ring that seals shut off valve into body of fuel pump. still no joy and still a drip - am considering doing the thing again in case it's been botched/misaligned or whatever and will also check out the maf. also had the engine management thing read with a computer thing and no codes present. not sure if there's anything else to add - the car drives very well, has plenty of go and responds well enough. there don't appear to be any leaks along the fuel line and i don't have any damp patches under the car when i check in the morning. no smoke coming out the back, either. any idea, please let me have them...

tia

mojo

 

[Hibbo]

How much does your caravan weigh?

 

[jberks]

Back to basics. The fuel has to be going somewhere is either leaking, not being burned properly or you actually need that amount due to some inneficiency such as low tyre pressure, binding brakes, a caravan etc.
Theoretically if it's leaking you should spot it (or you'll soon spin off into a crash barrier). If it's being thrown out the back, unburned, then you should be seeing soot whenever you boot it. In any case, the cO reading should be high which can be picked up by any MOT station.

I'd start with a cO test.

 

[Hibbo]

In any case, the cO reading should be high which can be picked up by any MOT station.

I'd start with a cO test.

Do they do a CO test on diesels?
I'm not sure if a diesel produces high CO levels like a petrol does when it runs rich.

 

[jberks]

Do they do a CO test on diesels?
I'm not sure if a diesel produces high CO levels like a petrol does when it runs rich.

I assumed they did. They do some kind of emmission test but as I understand it, they do it at high revs on diesels.
Could be wrong though.

 

[Hibbo]

I assumed they did. They do some kind of emmission test but as I understand it, they do it at high revs on diesels.
Could be wrong though.

I think it is just a smoke density test.

They just rev the breasts off it, and the probe has a light at one end and a light detector at the other.

Diesels have very different burn characteristics to petrols, they run very lean at all but full throttle, and ANY overfuelling simply results in black smoke.
http://www.youtube.com/watch?v=-gVUwDJ1QyY

 

[BarryG]

My consumption has been more recently, crossing fingers and just putting it down to the cold weather and lots of cold starts and lots of short journeys. Some of which probably haven't even got the engine hot.

Hibbo on the smoke issue, it only happened once on mine, whilst giving it some welly on the M1 with a relation following behind, a couple of months ago. Would this be normal?
I knew it had happened, without seeing anything in the rearview mirror. As there was a sudden surge for a couple of seconds. Haven't had the chance to give it a good run at speed lately.

 

[Hibbo]

Not sure if the normally aspirated om605 in your car has a mechanically or electronically controlled IP (mine's a N/A 606 and is mechanical), but either way, when you are booting it the engine is very close to its 'smoke limit' (the maximum amount of fuel that can be burnt given the air available), so a slight blip from the governor could give a burst of smoke. I wouldn't worry about it as long as it's not doing it all the time.

Most diesels will give less MPG in the winter, not just due to the heavier electrical loads (more use of headlamps, wipers, demisters etc) but becasue winter derv has a lower calorific value than summer derv.

 

[mojo7676]

thanks for the comments and suggestions. as i said, haven't noticed any dense black smoke, and, for the record: i got no caravan, nor do i plan on ever having one. will, however, seek to get the emissions checked in case that shows something unusual. tyre pressure was on about 22psi (ish) - have raised to thirty all round (advised by someone a few days ago). can't see it making much difference btu will see. also, checked brakes when serviced engines - all wheels roll freely when in neutral; no binding calipers or anything that i could detect.

will update when/if anything changes

mojo

 

[Blobcat]

Tyre pressures will a big difference, have a look in the fuel filler door for the correct pressures. If you raise them to the fully loaded pressures you can increase the fuel economy some more.

 

[BarryG]

Not sure if the normally aspirated om605 in your car has a mechanically or electronically controlled IP (mine's a N/A 606 and is mechanical), but either way, when you are booting it the engine is very close to its 'smoke limit' (the maximum amount of fuel that can be burnt given the air available), so a slight blip from the governor could give a burst of smoke. I wouldn't worry about it as long as it's not doing it all the time.

Most diesels will give less MPG in the winter, not just due to the heavier electrical loads (more use of headlamps, wipers, demisters etc) but becasue winter derv has a lower calorific value than summer derv.

Thanks for that Hibbo