just had my timing belt changed today. but I found my car's idling fuel consumption went up to 0.7 l/h, it used to be 0.5 l/h. Does it mean the timing belt replaced wrong?:(

Did a dealer do it?

no, it's done in my local garage. but no worries now because it dropped back today.

How do you get the idling fuel consumption then? My trip computer does not give an instantaneous reading at idle IIRC.

Bump. Honestly, how can I read my idling fuel consumption? I do not have Maxidot if that makes a difference.

My Octy has maxidot, but my Transporter has a half height display for the trip computer - I press the of the buttons on the end of the wiper control stalk to toggle between different displays (same as the Octy, but without the maxidot menu). What does it say in your owner's manual about the trip computer display ?

Re the increased fuel consumption at idle: Are you comparing figures with a fully warmed up engine in both cases ? (mine uses a lot more while it is cold). Is the AC pump now running ? (it will make the engine work harder when the compresssor is "on" duty (as opposed to not doing any work).

It's not the new timing belt that causes the problem. It has to be the tuning chip box I recently installed. Funny enough, during the day the idling fuel consumption maintains at 0.5 l/h most of the time, but at night it goes straight up to 0.7 l/h. I was thinking that may be it because there is more traffic during the day hence I accelarate much less. However I went to a remote area yesterday and there was even less traffic than at night, the idling fuel consumption figure was still 0.5 l/h.

I know when the engine is cold the figure is higher. the figure I am talking is after several hours of hard driving.

I don't understand why Gregoir can't see that figure, It's right on the computer screen when you start the engine. Is your car a modern car?

It's not the new timing belt that causes the problem. It has to be the tuning chip box I recently installed. Funny enough, during the day the idling fuel consumption maintains at 0.5 l/h most of the time, but at night it goes straight up to 0.7 l/h. I was thinking that may be it because there is more traffic during the day hence I accelarate much less. However I went to a remote area yesterday and there was even less traffic than at night, the idling fuel consumption figure was still 0.5 l/h.

I know when the engine is cold the figure is higher. the figure I am talking is after several hours of hard driving.

I don't understand why Gregoir can't see that figure, It's right on the computer screen when you start the engine. Is your car a modern car?

Presumably at night you have your headlamps on. These will place a load on the alternator and the engine has to work harder to drive it, hence the increased fuel consumption. No-one ever thinks of it but you must remember the more electrical loads you switch on the more fuel your engine will use. Many modern alternators can cope with loads of 100amps and more......

next time I'll leave the lights on during the day, see how it goes.

I was thinking that may be it because there is more traffic during the day hence I accelarate much less. However I went to a remote area yesterday and there was even less traffic than at night, the idling fuel consumption figure was still 0.5 l/h.

Now I'm confused - what difference would more or less traffic make to idling fuel consumption ? When the car is sitting still and the engine isn't driving the car it is idling, regardless of the traffic. Or are you referring to fuel consumption when the car is moving somehow ?

As well as turning the headlights on during the day, you could also switch your headlights off at night (as long as your car is parked somewhere safe when you do so).

Hi, railroad. you are a genius. I tried my car this afternoon, and it was exactly as you said. I've never thought head lights could make such a big difference.

Why I care about idling fuel consumption? because when IFC is 0.5, if there is no traffic, I can easily bring down my car's fuel consumption to less than 5 Litre/100 km. but when IFC is 0.7, under the same road condition, it's very hard to bring it down even closer to 6 Litre/100 km.

I'm glad you sorted it. The headlamps draw somewhere around 10 amps each. And then there's the side lights, number plate lamp and dash illumination lamps that are all on at the same time. On your car the engine control unit will adjust the engine idle speed to keep it constant as loads are added, but if you switch on the headlamps on an older car, and even then the heated rear screen and the heater fan you will notice how much the engine speed drops. If you had the means to measure the alternator output current you will see it would be quite considerable.

Always remember, in life you don't get anything for nothing. And that very much applies to engineering and electrical principles on cars too. So contrary to what any driving instructor might tell you always switch off any electrical loads you don't need to use 'cos you're paying for them, and you'll prolong the life of the alternator and battery at the same time......