99 C200 Sport with an unquenchable thirst

[IanMc]

I picked up a 99 C200 Sport Tourer on the weekend and drove it back from Leeds, cruising at 80mph pretty much all the way.
Whilst there are various little faults with the car, one thing is for sure - the petrol guage works!
I'd filled the motor up in Leeds and had to refill it again at the bottom of the M1.
A tank of fuel only got me 193 miles and returned a derisory 16mpg.
Has anyone had a similar experience?
I'd have expected to get a least double the mpg given the fact there was no 'foot down' acceleration going on.

 

[OmniCognateNeutronRangler]

my 2.6l V6 does around 30mpg on a decent run so your figures are certainly not what you'd expect. I'm sure some of the more technical members of the forum can offer some advice on what could be causing it.

One obvious question, can you smell petrol at all? I would have though that to get that bad economy it would more likely to be a leak than any kind of mechanical/electrical issue.

 

[The Hooded Claw]

in my C240 Sport i get approx 135 miles out of twenty quid & that is short stop/start trips around town

 

[ProfessorX]

I recently completed a 365mile round trip, filled right up before I departed and I now have just marginally over 1/4 of a tank remaining on my return.

 

[IanMc]

No smell of petrol, and no money left in my pocket!
Sounds as if a trip to the mechanic is in order (via a petrol station most probably ....)
Thanks for the input - appreciated!

 

[jberks]

Leeds to London taking it steady in that car and I'd expect 33 ish. That;s what my C220 returns anyway.
Probably running rich so I'd check MAS as a starting point.
How is she running? - ok - bit hesitant....?
If she's running ok I'd be looking for leaks.

 

[IanMc]

She's running fine, idling at 800, and didn't miss a beat on the 200 mile journey.
RPM in 4th at 80 was over 3000 though - I'd have thought it would have been lower.
I didn't realise having the 'EC' button off meant that the air conditioning was on though - will this have made any difference do you think?

 

[FIBAMAN]

You mentioned revs in 4th gear, is the car manual? I thought it would have 5 gears. My wifes 2000 C180 (2 ltr auto) returns 37 / 38 on a similar run including some use of climate.

 

[IanMc]

Its very much an Auto...
My point really was to state I hadn't kicked down a gear at any stage - it genuinely was a nice sedate cruise home (probably with a trail of petrol dripping behind me ...).

 

[OmniCognateNeutronRangler]

AC Shouldn't make all that much differnce, mine is always turned on. On a good run, i.e. an emptyish motorway I get 33-34mpg out of mine driving with the cruise on at the speed limit. Driving home from the office (about 75 miles on twisty country lanes at something approximating the speed limit) I get beween 27 and 31mpg. Strange that it varies so much, but it does. I'm guessing the lesser figures must be when I get caught in traffic.

I get around 350-400 miles out of a tank.

Have a look around the back, underneath the car for leaks. If it's a bit dark use a match........

 

[kid-jensen]

IanMc,

At the risk of repeating myself, common problems with injected cars that run well but guzzle petrol are:
1. leak
2. Too-high fuel pressure (maybe shagged pressure regulator)
3. Out of Spec Injection temperature sensor.
4. Obvious stuff like binding brakes, low tyre pressures etc.

Hope some of this helps.

 

[IanMc]

Thanks for all the above - appreciated.
I'll get the car seen to and let you know the diagnosis.
My fear is that the previous owner knew the problem existed but thought better of getting it repaired because of the cost vs value.
Anyway, there is definitely something wrong as the gauge has already worked its way down towards the 3/4 mark after only 30 miles of urban driving.
This is my first Merc - I only bought it as I was after reliability ...

 

[television]

I think that the cold start device is stuck or one of the sensors,temp or air.



Malcolm

 

[Glenn Smith]

She's running fine, idling at 800, and didn't miss a beat on the 200 mile journey.
RPM in 4th at 80 was over 3000 though - I'd have thought it would have been lower.
I didn't realise having the 'EC' button off meant that the air conditioning was on though - will this have made any difference do you think?

Has it not got a 5speed box? 3000 at 80mph is probably correct in top gear, i have c230k and easly get 30mpg even fully laden at 90-100mph on our runs to and from Holland and Germany, on the gauge this equates to about 100miles per 1/4 tank, or 300 down to the red, best was over 350 (not me driving). it seems odd that you are still running ok but theoreticly putting twice as much fuel as would be expected through the engine, at idle the motor would run very rough with this much fuel going through, at part throttle settings there is a much higher band of tolerance for incorrect air/fuel ratios, ie it could run very rich without you neccessarily noticing, perhaps you have a leak in the exhaust system or a blocked cat.

 

[IanMc]

Thanks Glenn - appreciate the input.
No, its a 4 speed auto box.
There's no issues on idle, and it runs smoothly through the gears - in fact it drives really well - its just extremely thirsty.
Pardon my (complete) ignorance, but how would a leak in the exhaust system affect fuel consumption?
If its running rich, does that suggest any expensive fix, or is it just general tweaking that's required?

 

[C220GJS]

Ian, probably the cheapest way to check if your car is overfuelling is to take it to an MOT testing garage and ask them to check the emissions for you.

 

[panason1c]

Thanks Glenn - appreciate the input.
No, its a 4 speed auto box.
There's no issues on idle, and it runs smoothly through the gears - in fact it drives really well - its just extremely thirsty.
Pardon my (complete) ignorance, but how would a leak in the exhaust system affect fuel consumption?
If its running rich, does that suggest any expensive fix, or is it just general tweaking that's required?

Surely you have the 722.6 transmission which is a 5 speed auto-box?......not changing up to fifth gear would cause excessive fuel consumption...

 

[television]

Surely you have the 722.6 transmission which is a 5 speed auto-box?......not changing up to fifth gear would cause excessive fuel consumption...

yes it does have a 5 speed box, the 722.6 as you say.

Malcolm

 

[stevie boy 01]

just thought i would ask ... have you found the problem yet as my c200 sport is ****e on fuel to .. about 100 miles on £20....

 

[IanMc]

The car is booked in for Wednesday, so hopefully I'll have a better idea then.
Have you had anyone look at your car Steve?