Ford C-MAX (2003 - 2010) - 06 1.8TDCi - MPG getting worse

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Thu 22 Nov 2007 15:50
06 1.8TDCi - MPG getting worse - Ravenger
My 06 1.8TDCi C-Max has now done approx 16,500 miles, and the mpg has dropped about 20% over the past few months. I used to get around 50mpg on my way to work, but now the weekly average is around 40mpg. Around town it's never been brilliant on the mpg, but its dropped from 30mpg to around 20mpg.

The engine seems to run ok - it doesn't cut out or stall. Doesn't produce masses of smoke. It has however got much more clattery, sounding more diesel-like even when warm. Obviously it will be more clattery when cold in the winter, but this is much worse than it was last year.

Additionally it doesn't seem as smooth as before. Is seems rougher, more prone to high frequency vibration, especially when idling. Also it doesn't seem quite as nippy as before.

I've switched over to use Shell and BP premium diesel fuels for the last couple of months hoping that it might help clean any unwanted deposits, but it hasn't seemed to make any difference.

It's still in warranty and I'm thinking about taking it to a dealer to get them to look at it, but as it's not actually broken down and the problems are fairly subtle, I don't have much confidence they'll be able to do anything about it.

Oh, and it definitely hasn't been misfueled. I'm utterly paranoid about it, and check the pump several times before fuelling.

Any ideas?

Edited by Pugugly {P} on 26/11/2007 at 21:49

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Thu 22 Nov 2007 16:00
C-Max 1.8TDCi - MPG getting worse - paulb {P}
Does it sound as clattery with the a/c switched off?

I had something similar happen to the Mondeo (2.0 TDCi) - turned out to be a combination of dodgy camshaft position sensor (compounded by a loose connection thereto) and an auxiliary belt tensioner that was on its way out (and taking the belt with it) at 33k miles.

Since these have been sorted out my mpg has gone up from about 42 to nearer 48 and no more clattering.

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Thu 22 Nov 2007 16:06
C-Max 1.8TDCi - MPG getting worse - 1066
my 2.0tdci cmax did 34 mpg in town all the time. at 20mpg there must be a real problem.
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Thu 22 Nov 2007 16:24
C-Max 1.8TDCi - MPG getting worse - Ravenger
Does it sound as clattery with the a/c switched off?


Oh yes. I don't have the AC on much at all.
I had something similar happen to the Mondeo (2.0 TDCi) - turned out to be
a combination of dodgy camshaft position sensor (compounded by a loose connection thereto) and an
auxiliary belt tensioner that was on its way out (and taking the belt with it)
at 33k miles.


That's interesting, because a couple of times recently there was a high pitched squeal from the engine from a second. Only when it was very cold though. Could be the belt slipping, if the pretensioner is on the way out.

I'll get it to the dealers to check out, thanks!
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Mon 26 Nov 2007 21:35
C-Max 1.8TDCi - MPG getting worse - wicked_buffy
It sounds like your timing has shifted dramatically. The camshaft position sensor is the obvious to look for. It might have becoming loose. Worth also checking the crank sensor as this is synchronised with the cam sensor. Any discrepancy could causing a timing error. Then there's the prospect of the cam belt slipping some teeth on the cam shafts...get it checked fast!
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