Fuel consumption. CDT to CDTi
 

I recently changed my 2002(52) 2.0 diesel CDT (110,000 miles) for a 2004(04) 2.0 CDTi. (125,000 miles) Both are Auto. Fuelwise I think I have made a big mistake!
The CDT regularly returned mid 40mpg and on a motorway, cruising at 65/70 mph would be around 50mpg +.
The CDTi is around 10mpg less in all ranges. No matter how gently I drive this I struggle to get it into the 40s. Certainly not worth the slightly
better performance.
Can anyone tell me if this is a normal difference between these two models.

As i do a lot of miles I will be looking for another older CDT.

Very interested in any comments,
Thanks.
Terry.

It's certainly true that the auto version of the cdti returns fewer miles than the manual version, but I've never returned less than 40 mpg in mine, and would be surprised to get anything less than mid 40s.

Servicing is important, consumption always peaks in the months after I've changed all the filters (including the pcv)

Assuming you've eliminated the basic things like having already had a recent service, ensuring that tyres are correctly inflated and making sure none of your brakes are binding, the next two things to check are that your MAF is functioning correctly (try driving with it unplugged for a couple of hundred miles) and that the EGR valve and/or exhaust manifold aren't clogged with a build up of tar and soot deposits.

My late (2005) ZT (with 18 inch wheels) diesel auto will return 45 MPG ish if I take it easy (60 ish MPH). Around 42 if not (going with the flow ;)).

It has been remapped to 160 ish as well.

Maybe it has been a town car mostly and needs an Italian tune up. Diesels don't like to pootle.

in addition to this sound advice, check that your car is getting up to temperature. If the temp gauge is not reaching quarter to, your thermostat has failed. You can fit a Renault 5 stat in the front hose rather than mess on with the awkward placement of the original. (Leave the old one in because it fails in the open position).

Proper temperature makes a heck of a difference to the efficiency of our diesels and if the stat has failed, fitting a new one will improve your mpg a lot.

The problem is not going from CDT to CDTI but the individual car itself.

Agreed. Auto box does effect the fuel but you need to learn how to drive the auto box. 50% throttle or less means it won't drop a gear.

Tbh best thing I ever did was a maf less map and change to 15s for my auto. Car. Drove better than ever.

is the only difference (CDT to CDTI) the 116 to 135 map?
if so the extra horses may explain some of the difference...

a 160 map and health check will go a long way to getting some back...

The OP has said that both of the cars are auto......

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Pretty sure nobody suggested they hadn't :}