Viano running problems poor mpg

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New Member
Sep 6, 2016
Mercedes vito
Hi all

I have a 04 plate viano, what mpg would you expect? Currently I do the same 50mile journey to work then 50miles back every day, you'd expect the mpg displayed on the dash to be the same or similar for each journey, one trip would be about 31mpg then the next exact same journey would be like 23mpg. What could cause such a difference.

Also when accelerating from stand still a fair bit of black smoke appears out the back, leads me to believe something is not quite right. So far all I've done is change air filter as I had a new one knocking around.
I have another Vito pretty much identical and that regularly gets 38 to 40ish mpg granted that's a manual and only has 5 seats where viano has 8 seat and is auto.

Only problems that may or may not be connected that I know of is- the lights come on with the ignition regardless of light switch position, the AC makes a noise at idle and doesn't blow cold until moving faster. The mpg is pretty much same no matter if AC is on or off.

Any help or ideas would be most appreciated as I have a long long drive next month that I really would like to have viano sorted before heading off.

The black smoke is probably the injectors and is also contributing to the low mpg. However we have always got 33mpg from new. It is always going to be less than the Vito as the Viano has much better performance.
I don't understand how one minute I get 30mpg then next the exact same journey I get nearly 10mpg less. I've bought some forte injector cleaner so will run that through, I'm used the petrol version on my bikes before with decent results so hopefully will help. Might give her a clean too. It's done 175000 miles, do you think maybe something like the cat or maf needs changing
It is always going to be less than the Vito as the Viano has much better performance.

Eh? The Vito and Viano are mechanically identical (so long as you're comparing equivalent versions).
My Vito is a 04 115 model 150bhp dualiner and the viano is a 04 150bhp model too so same engine. Few differences being viano is the extra long one and has 8 seats and it has air suspension other than that they are identical so I would have expected a pretty similar mpg from them both, viano being slightly worse due to being heavier but not 15mpg different between the two models
Would still think that the performance might differ. The Vito is commercial and requires torque at lower rpm the Viano has it more top end. No doubt someone will correct me but that is my experience of both. But you may well be right although as I said we have never got more than 33/35mpg and the higher on a long trip.
Other than comparing the Vito to the viano I'm also comparing the same viano doing the same journey in same conditions and I'm getting a mpg as low as 23, then i might see a mpg of 32 next time. I can't understand what would cause such a drastic change, even if you were really giving it the beans I'd still expect higher than 23mpg! I imagine the 3.0l one gets better mpg than that.
MAF.. disconnect it and see if the van runs any better.. also look for FORTE Diesel treatment, fire that through and see what happens... report back. If you have someone that can supply BLUECHEM its even better..try that and see how you go..
I'd still expect higher than 23mpg! I imagine the 3.0l one gets better mpg than that.

Not by much - ours averages about 25 mpg.

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