Poor MPG - Grand Scenic 1.5dci

Kylie Fan

Hi,
Wondering if anyone had any thoughts on reasons for low mpg on a new type grand scenic 1.5dci (110bhp).
Getting only 28mpg in short trips i.e.<3miles from cold
Only 35mpg in a combination of short and longer (20-30 min drives) and 40mpg at a constant 70mph on the motorway.
Driving style isnt a factor as i get 45/53/59Mpg from a 2.0TDI passat for the same trips.
I have read temperature impacts the mpg but dont see much of an impact with the VW.
I realise that real mpg is always lower than the official mpg (64mpg combined for the grand scenic!) but this is way off..

The figures i am getting are more the like figures id get from a 1.8/2.0 litre petrol engine rather than a 1.5 diesel.

thanks

Alanstrainor

When was it last serviced?

OldmanMondeo

Diesel only comes into it's own on long regular journeys. Stop start on a large car will drink the juice. Remember it is probably only 90BHP compared to 120+ for the Audi, 500cc smaller engine and both around the same weight. It also has the aerodymanic of a brick compared to the Audi.

miller50841

Sounds like it needs a good service and a possible DPF blockage short journey's kill modern diesel's

Kylie Fan

It has been recently serviced (<400 miles ago) by main dealer, dont know if they did anything with the DPF, Can they be unblocked?

Its not just short journeys, 100 miles trips at constant 70mph is still ~40mpg but maybe that is as a results of blocked DPF..

Passat is actually heavier than grand scenic (by ~100kg), has a bigger capacity engine with a bigger power output (140bhp vs 110bhp) so it surprises me that its mpg is so much higher

maidhc

Check the air filter first. Are the tyres inflated to the correct pressure?

Failing that you should book it in. A multitude of issues manifest themselves as poor MPG.... seized calipers, fuel injection problems, blocked exhaust gas recirc valves etc etc

miller50841

Kylie Fan wrote: »

It has been recently serviced (<400 miles ago) by main dealer, dont know if they did anything with the DPF, Can they be unblocked?

Its not just short journeys, 100 miles trips at constant 70mph is still ~40mpg but maybe that is as a results of blocked DPF..

Passat is actually heavier than grand scenic (by ~100kg), has a bigger capacity engine with a bigger power output (140bhp vs 110bhp) so it surprises me that its mpg is so much higher

The DPF can be tampered with that it will still pass the NCT and cause you no more problems if it is the problem.
They can be replaced at a big expense or cleaned or completely cut off from the system.

transam

its a french car , it has a mind of its own

Wheelnut

The engine is just too small for the car so it has to work harder.

Casati

Wheelnut wrote: »

The engine is just too small for the car so it has to work harder.

I disagree- it won't be fast but it should be at least as economical as a 140 bhp Passat - the co2 emissions would be lower with the Scenic. If the OP is getting up to 59mpg on the VW it sounds like driving style isn't the issue.

I'd bring the car back to the garage, sounds like they did something a bit dodgy during the service. DPF light isn't a big issue on the Renaults if driven on motorways fairly often- could be the EGR valve. Does the power out of it seems okay?

Wheelnut

If the problem is due to the DPF or the EGR valve these are things that gum up over time, so initially the consumption should have been better but the OP hasn't said that. The only other possibilities I can think of for a diesel are a (very) dirty air filter or a timing belt that has jumped a cog. However, I still think the engine is too small for the car.

Stallingrad

Are you basing your mpg on the trip computer, or have you worked it out manually?