W210 E320, mpg dropped since B Service

[englishdas]

That describes it in a nutshell really, just got it back from the garage, and although it now drives like a new un again, I'm getting mid 20's MPG. I took it to Leeds and back (round trip of 59 miles, and used about 15 quids worth of DERV. I was amazed to see the yellow light come on about 10 miles from home, and even more stunned as I watched the needle plummet through the reserve like a downed fighter jet for the next five miles til I got to a fuel station, all the while driving so carefully it wasn't funny.

As I said, it's just had the B service, I know the brakes got a replacement, the fanbelt has been replaced, and all the filters have been switched. I did get the Oil Warning, where it needs a bit of a drain down, I suspect there was a slight overfill, but I know if it's not absolutely bang on the monitors start worrying. But usually on a run like this, I'd get 40+mpg, at least, and that's being mildly heavy footed.

I guess I'm wondering, does it just need 'running in'? How to explain this to the garage if something more is the problem...

 

[renault12ts]

Can you be more specific?

£15? How many litres was that?

Yellow light? What's the significance?

It depends upon whether the yellow light was on when you fuelled the car.

 

[24 VRT]

I'd talk to the dealer and tell them whats happening and ask they check it over to make sure nothing was done wrong in the B service. But don't forget when it goes in for servicing the MPG will drop like a stone as the car is often left sitting around idling for ages - and if it goes out on a road test it won't be driven economically.
You indicate that the fuel guage was plummeting when the low fuel light came on - did you reset the fuel settings/trip computer after you filled it up at the garage, and if so are you still getting mpg's that are much lower than normal? If so its talk to the dealer time imho. Even more so if you are getting oil level warnings too!

 

[englishdas]

Yeah, I'm definitely gonna have a chat with him, I just wondered if everybody gets rubbish mpg after a service before everything 'loosens up' so to speak.

R21, Sorry, It had been hovering just above the yellow light (reserve) when I picked it up from the garage. I put 20 quid in just before my run to leeds. That was 14.5 litres. So my tank had 23.5 litres in it. As I set off to Leeds, I'd used a bit up (not much, My gauge was showing just over the 'quarter tank' mark). so i guess i had 20 litres. After 55 miles of driving, I was down to 9 litres. Theres no way I've ever used 11 litres of diesel to do 55 miles before.

Does this make things clearer, or confuse matters further?

By the way, my early morning run this morning, usually i get 27 to 29mpg on the display, but this morning I got 22.1mpg. It just seems way way off the performance I was getting.

 

[24 VRT]

I haven't noticed any deterioration in mpg after a service in the past - in theory there shouldn't be, particulalry if you have had a new air filter fitted, and there have been no adjustments to the fuel system.

 

[renault12ts]

It doesn't sound good.

A service should not effect your MPG.

It's almost as if a brake is dragging. They will have adjusted (I think) your handbrake, make sure it's not binding. This will be apparent if one or both rear wheels is excessively hot.

 

[englishdas]

Thanks R21, I kept thinking of that whilst driving, but then got distracted assuming I'd smell the brake heat (not sure I even know what I mean...)

But about to go for a run now, will check it out. I did have the brake shoes and brake expander swapped out btw at the service, so that could be it!

Oh, one more thing, My car was incorrectly fitted with 225 55 16s and they were pretty worn out, but now sits on the correctly spec'd 215 55 16s. This couldn't deteriorate MPG? The Circumference/radius is the same. just the width of tread has narrowed and is of better quality.

I think brake check required, while he drops some oil out....

 

[Stratman]

The new tyres are not the same radius as the old ones.

The '55' in the size isn't an absolute measurement, it's the sidewall height expressed as a percentage of the tread width. Your old tyres, with a 225 width had a sidewall height of 225 x (55/100) = 123.75mm. Your new tyres have a sidewall height of 118.25mm, which is just over 95% of the 225s.

Having said all that, it's unlikely that alone could account for the difference in fuel consumption.

 

[englishdas]

Now it's not everyday I learn something useful! Didn't know that Stratman. I suppose it would factor in then, but at you say, not to such a great amount.

I'm booked in for a check-up now, The garage sounds flummoxed but as they are great guys, they're pretty intrigued and wanna sort it asap. I doubt the MB Dealer would sound so passionate, though I could be stereotyping Dealers for which I apologise in advance to anyone offended

 

[englishdas]

John at JAR ran the car in this morning for a check. Did some work on the rear brake adjustment. It wasn't 'crawling' in drive, like it should, he noted, so after the adjustment, we had the necessary force needed for the parking brake and foot brakes, but none of the drag or resistance when not needed.

He did emphasize steady release of the parking brake, as the ratchet 'overspools' or the like...

Bottom line, drove it over there with a 26.5mpg reading, drove it back with a 35mpg reading. I know thats not scientific, but not having to accelerate downhill to keep up with traffic is a pretty good indication.

He drew off about 300ml of oil too, and the 'oil level' warning light has stopped shouting at me now.

Result. Also, did a gearbox reset. Was changing up at 1750-1900 driving steadily, immediately after, Change-up occurred around 1400-1600, again not scientific, but just eyeballing the needle.