carolyn_vdv

I wish this was the case. I was using the regular fuel for our car, after about 6 months the knocking started thought it was the exhaust or something and took it in to the dealer. They said use the premium gas from a reputable gas station (not Safeway/Co-op which I had been using). I changed at 10c more a litre and after a brief respite the problem is worse than ever. I think the gas stations are mixing their blends

Novocastrian

I suppose you could describe it as an estate car, here of course it's referred to as a 5-door hatchback. Same thing I would say. It's a 2.5 l engine and I've been getting 7.0l/100 km.

And as to your not being seen dead in it, firstly fine with me and secondly, a bit rich given your current choice of wheels.

iaink

Seems unrelated to me. The general gist is that a "premium only" vehicle can get away with using a lower octane level at altitude, so if there was a pinging/knocking issue then a lower octane would be one potential solution.

If the dealer is saying use higher octane is that because it should be on premium gas anyway and it wasnt? Modern engine management systems can adapt very quickly to variations in octane, but if its not designed to run on regular in the first place that would maybe explain.

The only difference really in the non name brand gasoline is the detergent mix, in fact often the different companies take fuel from the same depot before adding their proprietary blend of additives. Its maybe possible that cheap gas may need injectors etc cleaned more often, but in terms of octane etc it will be the same base fuel as the premium brands. I can only recall putting something other than "crappy tire" gas in my Civic once since I got it new in 2008, so if it sludges up I will know who to blame.

rivingtonpike

For what it's worth, we have a Dodge Journey which we love. It's comfy, quiet and roomy. It has the fold down seats 6 and 7 in the back. They're useful when people visit. It's true that when they're "up" the boot is pretty small - but then it's fine for day trips with the rellies.

Oakvillian

It might have something to do with oxygen content per unit volume of air at amospheric pressure, but it can't have anything to do with compression ratios. It's a ratio, innit: you're compressing the same volume by the same amount (so for a 4-cylinder, 2litre engine with a 10:1 compression ratio, every compression stroke takes 500cc of fuel/air mix and compresses it to 50cc). That 500cc of fuel/air mix will be a richer mix at high altitude (same amount of fuel, less oxygen), which would explain why you might want a lower octane fuel; in old-fashioned engines you'd just wind the mixture screw on the carb back a bit and carry on.

edit - just noticed your wikipedia link. The fount of all Internet knowledge is right, of course - there's a difference in absolute compression because you're starting from a lower pressure; but that still doesn't alter the ratio. There's just fewer molecules per litre of air.

Novocastrian

Just to put some numbers into this game, the scale height of the atmosphere (the average interval over which pressure drops from surface pressure to 1/e of that value) is 7.64 km.

So, we can deduce the following table:

Altitude. Percent pressure reduction.

1 km 12%
2 km 22%
3 km 31%

I think that's high enough for most purposes.

Of course the same percent reductions apply to the absolute O2 concentrations.

Dave n Ailsa

I have a completely different attitude to car choice.

I value drive quality over economy.

So yes, I will be paying over the odds for gas, insurance and parts, but I feel it's justified when you're on the road.

I have no other vice's, so cars are my guilty pleasure, lol.

I should mention that I do all the work on my cars, so I can buy cheap parts on the net and not have to fork out hundreds every time I need a spark plug ;-)

When we move to Canada, I plan on having, for Ailsa, something small and sporty, or maybe an Impreza WRX, and for me, I will probably have a crew-cap pick-up, and some sort of project car on the go.

I have a bmw 740i sport at the moment, so I'm getting used to the low mpg figures, lol. Worth it for the heated seats alone

Wait and see, we'll end up having a honda Civic 1.4 or something between us

Hey, I'm still at the dreaming stage

dbd33

My car is so equipped and I don't have to drive everywhere at 15mph preening.

Dave n Ailsa

Ummm, what does preening mean?

And you missed my point, I don't drive at 15mph, I have 300 horses and I'm not afraid to use them. How much do you spend on beer?

I bet I spend less on petrol than the average bloke spends on memory loss alcohol. (I don't drink at all by the way, and stopped smoking three years ago.

I'm positively well off, lol.

My seats by the way, show us yours

dbd33

It was a reference to the fact that BMW, like Buick and grey Toyota, is not a vehicle to choose to line up behind at the lights. The driver will dither, admiring his upholstery, rather than getting out of the way.


I've no idea how much I spend on beer (nor cheese or eggs). I attach a picture of one of my equines and wonder how one would cope with administering, and paying for, the farrier(s) for 300 of them.

I've never deliberately photographed my car seats (actually, no soft furnishings ever). I wonder if you might be better off with a hobby, going down the pub, for example.

iaink

Mine too. Heated seat are rapidly become the norm for canadian spec vehicles. the heated wipers on the sube are good too.

The reason I want 40mpg isnt the economy, its the environment. I actually give a shit.

dbd33

Heated seats isn't an option I would have ordered but I confess to being hooked. It may be that one can't see out of the windows for the first thirty miles but it's nice to be warm while driving by braille. I haven't tried heated wipers and don't imagine they'd address the problem of the blades being frozen to the shape of the windscreen at the parked position. The Beetle wipers cut two little grooves through the snow for the first half hour of operation and only soften to the right shape after that. Can you leave them heating overnight?

I assume that should be 40mpg, btw, even BMWs go at 40mph.

iaink

Imagine again

dbd33

Well then that seems like the sort of thing a man of sixty some years might like for Christmas.

iaink

I imagine mail ordering a vehicle presents certain practical difficulties, and are Irish spec vehicles likely to have heated wipers anyway.

Or were you thinking of someone else... Springless blade type winter wipers might be more practical...