Mpg plummets from 42 to 35 ???

[garystu1965]

Surely having new tyres fitted cannot produce this much of a drop ???
My car has just been taken into Mercedes for a startup problem. Intermittently fails to start. I wonder if they are connected.

 

[Bobby Dazzler]

Un-expected step changes in fuel consumption, either up or down, are a warning bell for faulty Air Mass Meters - often called other things like Air Flow Rate Meters, etc.

Get it checked out as running rich is bad enough, but running lean is a bigger problem, as it can lead to pistons overheating ...and melting!! Based on what you've said, it sounds more like rich than lean though.

I'd get it checked out as soon as you're able though.

HTH

 

[garystu1965]

Cheers. Actually it's been taken in to Mercedes for another problem (intermittent slow startup of engine). I've been told the injectors need replacing so that may be linked. Will having new injectors increase the performance ???

 

[Dieselman]

Only to the original standard.

Injectors would certainly account for the Mpg drop.

 

[jeremytaylor]

Culpano, are your injectors being replaced under warranty, or are you paying. Would be interested to know what the cost of them is, that's all.

On my experience, stay clear off any fuel additives (it does say so in the manual, but burried deep). My 270 smoked excessively on using Millers, even though the mix is very slight (1ml per litre).

 

[garystu1965]

Replaced under warranty but the mpg has dropped pretty drastically. I was getting about 42mpg on my 17 miles into work but now it's barely scraping 36mpg. I have new tyres which may explain it ????

 

[Thmsshaun]

Cant see tyres having that much of an effect if anything new tyres inflated to the correct pressure should improve it slightly.

Are the tyres the same width as your old one. Even if they are not I couldnt see it accounting for such a drop.

 

[Dieselman]

Cant see tyres having that much of an effect if anything new tyres inflated to the correct pressure should improve it slightly.

Are the tyres the same width as your old one. Even if they are not I couldnt see it accounting for such a drop.

No, changing from Eco/Energy tyres to regular will see about a 7% increase in fuel consumption.

 

[Thmsshaun]

No, changing from Eco/Energy tyres to regular will see about a 7% increase in fuel consumption.

Didnt think it could effect so much.

oh well you learn something every day.

 

[Bobby Dazzler]

No, changing from Eco/Energy tyres to regular will see about a 7% increase in fuel consumption.

Still leaves about 10% un-accounted for though.

 

[FlossyJCLK]

Hey Culpano - I have heard of this issue in the US on some of the S-Class models. The best thing I have heard is to have the transmisson checked. This is the only thing that would cause such a huge drop. Have to agree with Thmsshaun, the tires would never cause such a drop. I added 18 inch chrome wheelies to my CLK, and I didnt see much of a loss. This is with wheels and tires that I know for a fact are not set for Merz. Good luck Buddy!

 

[jeremytaylor]

Replaced under warranty but the mpg has dropped pretty drastically. I was getting about 42mpg on my 17 miles into work but now it's barely scraping 36mpg. I have new tyres which may explain it ????

Sounds as if the injectors may still be to blame. I know with older-tech diesels you need to get the timing right with replacing injectors. Not sure if the same applies in the age of common rail/ECUs/etc.

...just because the injectors have been replaced doesn't mean they aren't to blame! Don't think the tyres are to blame. Anyway, I don't think you can get Eco/low resistance tyres in your size (17" with a 45 front 55 rear profile, if I'm not mistaken).

What sort of a drive is your 17 miles to work? My 25 miles is 25% open road/dual carriageway, 75% London traffic, and I usually average 31-33 mpg. Seriously gridlocked traffic sees it drop below 30, but pure open roads is 45+, unless I'm giving it some wellie.

 

[garystu1965]

Just booked it in with Mercedes Macclesfield. These people are most helpful. Can't do enough.