XC70: General Mpg /ac

[yostumpy]

Went for a drive to Folkestone today (80miles +/-) after filling up, steady 60mph, AC off, Roof bars/bike rack off. The last bit near Dover was solid with traffic but I managed to wiggle my way thro' and used s/s etc. parked up, and readout said 52MPG! (will be around 50.5 mpg in reality) Not bad.

On way home, car did a regen quite soon into the journey which knocked it down to below 46mpg, then started to creep up once finished, but I had the AC on as it was a bit stuffy , having been parked in the sun all day. So I kept at a steady 60mph, light throttle keeping the instant readout as steady as i could, then turned off AC. Well, the ECO gauge raised 2 segments, then after about 4 seconds the instant mpg increased bit by bit approx 2-3 mpg! Turn on, down it goes, along with the ECO gauge. So I 'pulsed the AC, On for 1 minute to chill the air, then AC off and the fan on low, kept blowing this chilled air for maybe 10 minutes. managed to get back up to 48mpg on return.(160miles total)

[monkeh]

Impressive - I'd still sacrifice MPG for comfort though. Coming from an era of MK4 escorts to non a/c'd 740's then getting a 940 with a/c... On an incredibly hot day, A/C is a must. Detesting sitting on black leather seats with warm air being forced around you, windows down, having to put up with buffeting and wind noise. I would prefer to spend that little more and be in comfort.

It could also mean that the pump may be a little stiff? The way pumps are designed now means they are a lot more "free spinning" than older design pumps.

I remember a laguna 2.2 n/a diesel I owned, I had to switch the a/c off before tackling specific hills on a run to West Wales. The pump was tight, Engine gutless. But still, No matter how hard I ran it, returned 45-55 mpg.

[mjk164]

My 2009 V70 SE D Auto, D5244 T5; I would recommend always leaving the AC on and selecting Auto and only change the temp setting and change the cabin air filter regularly. My car regularly gives 45/6 mpg with the cruise control at about 68mph. Comfort first!

[40t]

Have always been surprised, given the size of the D5, what a big impact the aircon has on the mpg. Interesting point about the pump.

[monkeh]

Originally Posted by 40t

Have always been surprised, given the size of the D5, what a big impact the aircon has on the mpg. Interesting point about the pump.

I tried today, 110 mile trip. All motorway up until 30 miles from destination.
A/c made half an mpg difference. A steady 70mph because my passenger is my speed limiter. Anything over 75, I begin to get an annoying noise in my left ear.
Back to subject, I'd think about checking the pump. Given how freely the pump spins engine off, I'd suspect something is up with yours. On a remapped d5 (225 minus egr) , at 70 mph, with body lift, muddy tyres, loaded to the gunnels... 39.5mpg. A/c off, I touched 40 mpg. And all using cruise control, very minimal braking.

[40t]

Thanks Monkeh, will do

[Tatsfield]

Anything that the engine drives will cause more fuel to be used. Some cars seem to have a/c systems that really burn fuel but I suspect that in the more recent years, with climate control systems requiring the a/c to be running most of the time, the designers will haver looked at the fuel cost of so doing and designed the a/c to be as fuel efficient as possible. I'd like to think that my XC70's D5 lump takes driving the a/c in its stride and that while it's doing it, the extra fuel consumption is kept to the lowest level. We always used to talk about 2 to 3 bhp drag for a/c and years ago I can recall, when low on fuel and sweating on finding a petrol station before running dry, I would turn off the a/c in the hope that it would give me the extra mile in the tank to reach a pump!

[yostumpy]

Cars used to have a vent grill below the windscreen ,in the scuttle, so that fresh ? Outside air would be forced in to the cabin at normal speeds, then increased via the fan. On the XC there doesn’t seem to be this, so when fan is off, no detectable air comes through the vents. Bit weird.

[apersson850]

Older AC systems, like in the 700-series, were on or off. When the compressor was running, it took the temperature down to about 2°C. Then you mixed in warm air to get a comfortable temperature in the cabin, as needed.

Today we have variable displacement compressors, so they just cool down as much as required to keep the cabin at the desired temperature.

Note that savings in fuel consumption are frequently compensated by premature compressor failure, if you don't use the system. They normally fair best being used. Just leave the system in AUTO, and it will run as much as needed.

Today's FWD cars both have a more cramped space for the ventilation system, and tend to have more parasitic heating. That is, the air is heated by the engine just by passing nearby more than it was with the more spacious engine compartments in the cars with longitudional engine mount and rear wheel drive. This implies that the fan running at slow speed has become standard all the time today.

[BigGreenThing]

Originally Posted by yostumpy

Went for a drive to Folkestone today (80miles +/-) after filling up, steady 60mph, AC off, Roof bars/bike rack off. The last bit near Dover was solid with traffic but I managed to wiggle my way thro' and used s/s etc. parked up, and readout said 52MPG! (will be around 50.5 mpg in reality) Not bad.

On way home, car did a regen quite soon into the journey which knocked it down to below 46mpg, then started to creep up once finished, but I had the AC on as it was a bit stuffy , having been parked in the sun all day. So I kept at a steady 60mph, light throttle keeping the instant readout as steady as i could, then turned off AC. Well, the ECO gauge raised 2 segments, then after about 4 seconds the instant mpg increased bit by bit approx 2-3 mpg! Turn on, down it goes, along with the ECO gauge. So I 'pulsed the AC, On for 1 minute to chill the air, then AC off and the fan on low, kept blowing this chilled air for maybe 10 minutes. managed to get back up to 48mpg on return.(160miles total)

That's a really good mpg to be fair! I went for a manual D3 XC70 (1.98L 5 cylinder) because I couldn't justify the 4WD need on such an infrequent basis in the South East of England and I was looking for big/safe estate to transport family with fair mpg. Best mpg I've ever had (when we had the notorious fuel-drought) was 47.1 mpg on a trip (but calculated on a rolling basis) on my own and vehicle unladen. The journey on its own I calculated at 49.16mpg. I was quite happy with that!!


So, in years gone by 55-57mph, was the average speed for achieving maximum mpg. This was at a time when 5 gear manuals were growing in popularity, taking over more and more from 4 gear manuals.

SO, my question is, with 6 gear manuals (or automatic gearboxes with more gears) - what is the considered "optimum speed" to yield the greatest MPG?

Is it 65mph in 6 gear?

Looking at Real MPG by Honest John, these are results of mpg: https://www.honestjohn.co.uk/realmpg...rive-startstop

Albeit mine's not a "start stop" version of D3 model, I'm returning 43.3 mpg on average (with a/c toggled between on and off) from a 2litre diesel pulling 1.8 ton of car (and not the 2.4 D5). I only have to breathe on the accelerator for the turbo to kick in lol...so I tend to breathe very gently!

This topic has probably been done a gazillion times...but I've a long trip over Bank Hols - so I'm going to fill up and trial leaving a/c on the whole time...see if the average drops below 43.3mpg.

Incidentally, I've seen no real increase in MPG between stock/normal pump diesel and the premium stuff...just a slightly bigger hole in my wallet!