Is the trip computer honest MPG wise?

[DaiRees]

I've verified my trip computer a few times and always found it to be very close, but on each occasion it read UNDER by 1 or 2 mpg. So if yours is like mine you're actually doing ever so slightly better than the computer says.

[Doggy]

Mine's pretty much spot on too.

[paulb2004uk]

My 90 is pretty accurate unfortunately. Between 33 and 34 mpg.
Computer shows average speed of 14 mph... God I need to find a motorway

[GTXJez]

Not the same engine I know but I have a 2.0 16v HPi (rare lump) GTX gearbox and final drive so at 80mph I am doing 3,600 rpm.

Just done 1,297 miles to Scotland and back all sorts of roads and speeds, the computer said 36.7mpg - I did a tank to tank full and I worked it out at 38.2!

I can get 94mpg at 30 mph downhill with the wind behind me as low as 14 uphill from cold, foot to the floor even less - the conditions a have a huge factor on it.

But a friend has a 2.2 HDi GLX Saloon Manual, and swears he gets 45 mpg regular across all conditions
We had a D8 Estate 2.1 TD and from Edinburgh and back we got an average of 45 no bother! so the 2.2 should be at least the same?

[OdinEidolon]

Half a tank so far and I'm at around 550kms, but I'v done a lot of city driving too, so I'm pretty happy.

[DaiRees]

Just done 1,297 miles to Scotland and back all sorts of roads and speeds, the computer said 36.7mpg - I did a tank to tank full and I worked it out at 38.2!

I can get 94mpg at 30 mph downhill with the wind behind me as low as 14 uphill from cold, foot to the floor even less - the conditions a have a huge factor on it.

Your MPGs are about equalling mine then Jez, got it over 40 a few times on a run though . Is yours an estate or a saloon? Nice to see your actual is also slightly better than the computer says.

As far as the 2nd line goes, you can't be trying hard enough , I regularly get mine to read "----" going downhill (infinity MPG ) and I've had single figures going uphill when cold , mind you I do live in "the Valleys" so our hills are proper hills

[OdinEidolon]

...snip...
regularly get mine to read "----" going downhill (infinity MPG ) and I've had single figures going uphill when cold , mind you I do live in "the Valleys" so our hills are proper hills

Of course it'll read --- when going downhill at over ~1500rpm: the engine will cut-off fuel and the car will consume zero.
It's a normal fuel saving feature introduced at the beginning of the 90s I think.

By the way I live in the Dolomitis so here we have proper mountains, not hills... i'ts a pain to read 30l/100km on the MFD.

[DaiRees]

Of course it'll read --- when going downhill at over ~1500rpm: the engine will cut-off fuel and the car will consume zero.
It's a normal fuel saving feature introduced at the beginning of the 90s I think.

By the way I live in the Dolomitis so here we have proper mountains, not hills... i'ts a pain to read 30l/100km on the MFD.

Cheers mate, I somehow feel that my intended tone didn't translate very well I feel like I've been told off Good to know your mountains are bigger than my hills!

[highlander]

The fuel-supply cut-off thing is something I've been thinking about and trying to understand.

How the hell does it work? The engine continues to turn over due to its normal combustion process - this requires fuel, but if none is being supplied to the engine, how is it still running?

[DaiRees]

Because the motion of the car keeps the engine turning over even though you have your foot off the throttle, the engine is being driven through the gearbox by the wheels. The ECU detects that this is the case and completely cuts off the fuel supply, saving fuel. That's why it's more economical to leave the car in gear and roll down the hill than knock it into neutral (like our dads used to ), which would still use a little fuel to keep the engine ticking over.

Actually my dad used to turn it off altogether when going down hill, but that's another story

[highlander]

OK, but I would have expected the engine to suddenly go very quiet, simply because there's no combustion occurring. This doesn't appear to happen.

[DaiRees]

There's a lot of noise when an engine's thrashing about, not just the actual bang bit but all the other stuff like induction and exhaust, plus transmission, road and wind noise, I'd be surprised if anyone can pick out the individual combustion processes, at 3000rpm that'd be 100 "bangs" a second . That said there's definately a change in tone when you're on overrun.

[OdinEidolon]

what he said.

[OdinEidolon]

Of course it'll read --- when going downhill at over ~1500rpm: the engine will cut-off fuel and the car will consume zero.
It's a normal fuel saving feature introduced at the beginning of the 90s I think.

By the way I live in the Dolomitis so here we have proper mountains, not hills... i'ts a pain to read 30l/100km on the MFD.

Cheers mate, I somehow feel that my intended tone didn't translate very well I feel like I've been told off Good to know your mountains are bigger than my hills!

Oh, I didn't see anything wrong with your post actually! Probably my answer didn't seem too kind due to the fact that my English isn't that good at all. If so I beg your pardon, sir!

[GTXJez]

Got some BIG HILLS in Scotland! same applies though