Xantia - fuel economy down

[Jaf]

Hi folks. Fred has always done around 950kms a tank in the winter but the last 2 tanks I've struggled to get even 800kms. I've not put the air con accidently on! Cold start is a bit more difficult so I have 1 or more glow plugs gone. She drives well, same gears for the hills, and passed her emission test last month. There's a little smoke on start up, but I think that's from the dodgy glow plugs. No visible smoke when driving. No fuel leak that I can see, park in the same spot and no puddles.

So what to check? Air and fuel filter...anything else?

Thanks!

[Northern_Mike]

Filters, glow plugs - and do they use winter diesel in Spain? I believe in UK they use a different formula and it's never quite as economical. Maybe they've started doing that in Spain..

[Jaf]

Thanks. Hmm don't think so but I'll ask. I've always thought engines ran better in the winter? I've had the car for 7 years though so she is probably due an injector check, even though there's no smoke.

[MikeT]

I would be suspecting either or both filters you mention and check the tyres pressures too.

[Estately]

Hi Jaf,
Just a quick thought, it may be worth checking the thermostat, we have experienced Citroen thermostats both sticking open and closed which went unnoticed until there was a change in the ambient temperature. (Non Citroen bought for the Xantia from a factors in Spain cost about 20 Euros say four years ago.)

When changing one, loss of water is not great particularly if done with a cold engine and the car is parked on an up slope on the thermostat side of the car.

If you do not think that the thermostat has been changed for some time (if at all) take care with the three 10mm bolts, the last thing you want is for any of them to snap.
My method is to first try and tighten them by the tiniest fraction possible and then ease them out one flat at a time and squirt an easing liquid of your choice down the thread if it does have a tight feel. Consider loosening each bolt with the other two at the “at fitted tightness”. Others on this site who have done the job more recently than me may suggest an alternative method of removal.

On replacement I would grease the threads whatever state they came out in.

Hope that helps.

Andy.

[Peter.N.]

I have found the economy to be better in warmer weather, my 406 Hdi which normally does around 60 mpg on a long journey managed 67.8mpg over 650 miles coming back from Scotland on a hot day, 25C+.

The combustion is not quite as good when its hot except that the Hdi being electronically controlled compensates for the less dense air, the real saving comes from the oil and grease temperatures being higher and causing less drag, another factor is the less dense hot air causes less wind resistance and of course the engine reaches normal operating temperature quicker.

Peter

[CitroJim]

Check the brakes aren't binding. Even a little extra rolling resistance can down the economy markedly. So can faulty tracking too.

[Jaf]

Ok that's some more things to check. Thanks all.

Is there a system to put more fuel in whilst the engine is cold? I have a petrol car with mechanical fuel injection which has both fuel inrichment, via a 5th injector (cold start valve) and an air damper (warm up regulator).

I will of course check the simple things first!

Thanks again.

[CitroJim]

Is there a system to put more fuel in whilst the engine is cold? I have a petrol car with mechanical fuel injection which has both fuel inrichment, via a 5th injector (cold start valve) and an air damper (warm up regulator).

No, there's nothing like that on a diesel Jaf. Diesels need no cold fuel enrichment like a petrol, just a bit of pre-heating, post-heating and a faster idle, none of which will affect overall economy...

[Peter.N.]

Although there is no 'enrichment' mechanism on a diesel it does use a lot more fuel when cold purely because the engine is running inefficiently. On the same trip referred to earlier the first few days were very cold and the fuel consumption on a fairly flat but traffic less road was around 50 mpg, rising to 60+mpg once hot.

Peter