shockingly poor mpg, varies

[rtha6551]

recently I've been getting 40 miles to £10, rather than the 70-80 I used to, and that's not taking it past 2200rpm where possible

It does say 600 miles to next service on startup and I have put budget 195/45/16 tyres on the front but surely they can't halve my mpg?

Managed 67mpg on a run sat at 60-70mph on the weekend which seems normal, but back in town it's struggling to get 30! -.-

Any ideas?

[Dean]

Tyres do make a bit of a difference on MPG, but not that much I wouldn't of thought.
Had a look at the fuel filter? Injector seals alright?
What brand of fuel are you putting in?

[Toms306]

Hmm, those figures don't look accurate to me lol, it cant change so much!

Wheels and tyres will make a difference but not that much.

It has been cold lately though, might just be that you're doing short slow journeys without the engine getting up to temp?

[Poodle]

Does seem odd that there should be quite such an extreme drop, are you sure of your figures? That said, being at the tail end of your service period, poor tyres, short, stop-start journeys and cooler weather will all increase fuel consumption, so it is possible the combination of all those factors has made the difference.

[rtha6551]

Hmm, those figures don't look accurate to me lol, it cant change so much!

Wheels and tyres will make a difference but not that much.

It has been cold lately though, might just be that you're doing short slow journeys without the engine getting up to temp?

I do it by waiting till it hits the red light, putting x amount of fuel in and using an online calculator to work the mpg out

Using diesel from a jet garage, I'm thinking the gauge might be faulty as I can squeeze 60 miles out without the needle moving from just slightly touching the red :S

As for journey lengths I tend to keep the car running between journeys of between 3-5 miles each way, I don't rev it hard especially in the cold

[Jonny81191]

Just fill the tank and calculate it properly, brim to brim. There's no way you should trust a french gauge to measure fuel accurately!

[Toms306]

I'd work it a bit in the cold tbh, they take forever to warm up otherwise, and its not an XUD/TU so the headgasket shouldn't break from that.

As Jonny says though, red light to red light isn't accurate with any gauge....and especially a Peugeot one lol! Do a proper brim to brim and see what happens.

[Poodle]

3-5 miles isn't enough to even get the engine warm, so i'd say that's not miles off what i'd expect from these engines under those conditions.

[Toms306]

I thought he meant lots of those short journeys...as a delivery driver or something. I might've read too much into that though.

[Poodle]

Fair point, could well be i guess.

That's a thought, have you tried taking it for a rag, then trying again? All this pootling about has probably sooted up the exhaust good and proper, clearing that crap out should help.

[rtha6551]

It's true I shouldn't trust a French gauge especially when hills make it read differently as well!

I gave it some boot last night and the view from the rear mirror was cloudy lol so hopefully it's cleared it a little

funnily enough I was getting the 70-80 miles driving it harder than I do to get 50-60, odd one really

On the way home from work it's about 9 miles, 30-50 speed limits and the car is only just hitting 75 temp about 4 miles from home when I drive it steady, guess that explains a lot :p

[Poodle]

Fingers crossed fella, let us know how you get on, if you'd be so kind.

I have that problem, 8 miles to work, still havent hit 80 degrees by the time I stop. Need to get the preheater fixed, should be worth it's weight...

[Jonny81191]

The thing I've found is if you try too hard, the mpg can drop. Diesel engines like to be worked a bit. Also it's so much more efficient up to temp, so driving like your gran may have a detrimental effect.

[Poodle]

Exactly that - ride the torque, thats the key. Labouring the engine can be worse for fuel consumption than ragging it. Fairly sure the lowest bsfc is somewhere between 1700 and 2300rpm, depending on age, mods, mapping, and numerous other factors. Either way, that's the range you want to keep it in.

[Toms306]

The thing I've found is if you try too hard, the mpg can drop. Diesel engines like to be worked a bit. Also it's so much more efficient up to temp, so driving like your gran may have a detrimental effect.

Totally agree with this!!

In the Vectra handbook it even specifically says not leave it idling cold but to start up and move off as soon as possible (not sure this means WOT though... ). And it does make a huge difference. I know they're not deadly accurate but watching the 'current' mpg reading on the dash, it rises dramatically when the temp gets above ~80c so I do drive a bit harder to get it there sooner....if I set cruise control at 40mph it takes forever to warm up and uses a lot more fuel as that B road is basically the only kind of journey I do.

I also found the HDi liked to be worked hard tbh, I tried to get decent mpg from them by driving how I drove the Golf for mpg (major fail as the Golf was VNT so efficiency was lower down the revs!) and soon realised the mpg wasn't that great....so I drove 'normally' (read: hard) and the mpg rose....only car I've ever had that liked being ragged lol.

[Jonny81191]

My 406 gets mercilessly ragged about the place and returns low 50's. That'll do me!

It also warms up incredibly fast, warm air from the heater in sub 1 mile downhill in a 30 limit. So I suspect that helps.