CDT auto poor fuel economy

[Busboy]

I've had my CDT auto tourer nearly 10 years now but just recently I've been doing more mixed driving this being a combination of local roads "A" roads and a bit of motorway, now I'm of a certain age I don't fly about any more and tend to drive with my eve on the rev counter as well as the Speedo of course and rarely go over 20k RPM and let the box change up naturally. I'm keeping records of my fuel
consumption and normally top up with standard Diesel at 45 LTRs a time ( 10 gals) I've calculated that this is
getting me around 300-320 miles which equates to 30-35 mpg give or take. my car is regularly serviced and has the
oil changed every 6-8k miles but had never had the MAF changed and I'm wondering if this is something I should consider. All comments most welcome! ( by the way my car does not have a high line IPK so I can't check the fuel consumption by this method)

[grivas]

Originally Posted by Busboy

I've had my CDT auto tourer nearly 10 years now but just recently I've been doing more mixed driving this being a combination of local roads "A" roads and a bit of motorway, now I'm of a certain age I don't fly about any more and tend to drive with my eve on the rev counter as well as the Speedo of course and rarely go over 20k RPM and let the box change up naturally. I'm keeping records of my fuel
consumption and normally top up with standard Diesel at 45 LTRs a time ( 10 gals) I've calculated that this is
getting me around 300-320 miles which equates to 30-35 mpg give or take. my car is regularly serviced and has the
oil changed every 6-8k miles but had never had the MAF changed and I'm wondering if this is something I should consider. All comments most welcome! ( by the way my car does not have a high line IPK so I can't check the fuel consumption by this method)

Hi, does your car have a Webasto FBH fitted, and if so has the thermostat ever been replaced, this is known to fail overtime by staying open so the engine never reaches the correct operating temperature. If that is the case the FBH stays on much longer than normal thus using more fuel.

[Busboy]

Originally Posted by grivas

Hi, does your car have a Webasto FBH fitted, and if so has the thermostat ever been replaced, this is known to fail overtime by staying open so the engine never reaches the correct operating temperature. If that is the case the FBH stays on much longer than normal thus using more fuel.

Hi thanks for replying, my car doesn't have FBH and was fitted with a "Jules" in lineline thermostat 8 years ago and reads bang on "quarter to the hour" when warm

[Ed3]

I have a manual CDTi 2005 which may have met your 75 near the production line. I often wonder how I can improve fuel consumption back to the good figures that it should have, as sometimes it's bit 40 to 55 mpg when I do longer journeys. While we wait for those who know more about the correct running of the engine, I do two practical checks.

Firstly after a journey I check each wheel using my hand to feel for any heat as a sign the brakes are binding slightly. I have had a problem with sticking brake calipers causing binding and they can suddenly start to go wrong so I often check for heat on wheels after driving.

Secondly I look for fuel leaks near the rear right UK driver side area. There is the pipe going from fuel cap intake to fuel tank but I am more concerned about the fuel pipes going to and from the fuel cooler underneath at the rear of the rear wing. I have not a leak but there are signs of deterioration and the earth of the cooler has rusted off and when doing the rust paint underneath I found the fuel intake pipe clips were too rotten and fell off (so I replaced them). But which makes me wonder when the fuel cooler will leak in some way. Obviously we don't need to always crawl under the car but keep look for stains on the floor and I often use mirrors even very large ones laid on the floor.

[grivas]

Originally Posted by Busboy

Hi thanks for replying, my car doesn't have FBH and was fitted with a "Jules" in lineline thermostat 8 years ago and reads bang on "quarter to the hour" when warm

Okay that is fine, I assume you have checked the obvious things,tyre pressures, binding brakes, clean air filter new fuel filter.
You can try and see if adding a quality injector cleaner in the fuel might help, also clean the EGR valve and the inlet manifold, all these will help to some degree.

What grade engine oil are you using?, in the winter I use a full synthetic 5w 40 gives better and faster lubrication, then in the Summer go back to semi synthetic 10w 40.

[Brunty]

my cdti auto normally does around 38mpg using brim test every fill up, on a good run could go to 42 mpg noticed noise from rear wheel and mpg dropped to 34 mpg rear offside getting warm. new brake calliper now fitted, should go back to normal.

[2L-Diesel]

I also get about 38 - 42mpg on brim test on my 2003 auto 160 remap

I used to get about 46 on my previous 2004 facelift manual.
Stuart.