1.9 vs 2.2 TiD - Real world economy differences?

[Kev_Mc]

I'm getting an average of 32 mpg from a 2.3 HOT Auto.... so 36 from an oil burner is disappointing

I would only be able to make a real comparison if I happened to be able to borrow a 2.3 HOT Auto for a while.

How many of us have the chance to run actual back-to-back tests for this sort of thing? It's only going to be those that have actually made the switch from petrol to diesel - or vice-versa - without any other altered circumstances that can really tell us!

I part exchanged my old 2004 9-5 Aero auto estate for my current 9-5 TiD. I was averaging around 28mpg, and that was with lots of motorway work. Driving dangerously slowly on the motorway (tried the 72 mile journey home once doing 56mph on the M1) and it got up to 36mpg. I suspect if I drove that slowly in the TiD I'd be mid to high 50's mpg.

[Steve440]

I did a trip last year in my 2002 Aero Estate and over 200 miles managed just over 40mpg. I did not exceed the speed limit, I kept it above 55mph apart from a couple of minor hold ups and 80% of the trip was on motorways.

In normal driving I enjoy the car a lot of the time and with a mix of driving from 2 mile trips to the shops and probably at least one long trip a week I average just over 30mpg. After an hour on the motorway the SID usually is showing mid 30's. Using cruise does pay as without it I find the speed creeps up.

When checking the SID against brim to brims it is usually about the same bar maybe 1mpg.

Something I have found makes a big difference is tyre pressures, have them a few psi low and the mpg can drop by as much as 5mpg. Never had a car affected so much by tyre pressures.

Steve

[Norfolk Jim]

My auto aero estate was good on motorways and got up to 40 but drop below 45 and petrol went AWOL. My 2.2 diesel is excellent.

Just come back from weekend up north for a wedding. Mixture of slow driving from Norwich to Newark A1 junction - loads of lorries so average speed around 45 with bursts to overtake (SID showed 56 most of the time) then on A1 up to M62 to Bradford - averaging 75mph SID then showed 52. Then very slow traffic and crawl through Bradford on A650 through to Keighley and SID showed 47. Next day after wedding - 5 up and up to Malham Cove for walkies and back - so around 25 miles twisty roads. Then yesterday easy drive back through Bradford area and down A1 only taken off for a few miles around nasty accident then a nice cruise home albeit raining.

So quite a mixture and arriving home SID said this morning 49.8. Filled up again which worked out to 49.1 - so SID pretty accurate for a change. I'm pleased with this as the aero would have been around 30 overall

[steventon95]

Most impressive. Just come York to Oxford on reasonably clear roads M1 / A43 / M40 / A34 and still only getting 42.5 per gallon. That's with aircon off and 35 psi in the tyres all round. Should I go a bit higher perchance ?

[CitTone]

I've got the 17" wheels and run 38psi. At 70 with Cruise on, it will show about 44mpg over any decent distance.

[TomPaine]

No idea whether it'll make any difference to the economy but I find 35 too low and wallowy. I'm at 39/38 standard.

[Petemate]

All interesting. I run my tyres as per the handbook at 35 all round. Economy I feel is quite good considering I drive at warp speeds a lot of the time. The car has never felt other than sure-footed, except when I have the winter tyres on. Any higher pressures would rattle my teeth on the cr4p roads in our village....
Pete

[Norfolk Jim]

I run mine at 38 and it seems to help. Bazarly it feels more comfortable with higher pressures!

[Steve440]

Yes I agree high 30's feels better than mid 30's. I tried 40psi but was worried I might ware the tyres out to quickly even though it fine.

Another item that can cause bad mpg is a faulty thermostat, even though my gauge was showing midway in fact it was running cool. A new genuine thermostat ( under £10 ) brought it back up to spec. If the engine is running cool the ECU will be adding fuel.

Steve

[Petemate]

Yes I agree high 30's feels better than mid 30's. I tried 40psi but was worried I might ware the tyres out to quickly even though it fine.

Another item that can cause bad mpg is a faulty thermostat, even though my gauge was showing midway in fact it was running cool. A new genuine thermostat ( under £10 ) brought it back up to spec. If the engine is running cool the ECU will be adding fuel.

Steve

Blimey Steve - that is interesting, and although I am happy with my mpg, I'll bear that in mind. BTW - how was that discovered?
Pete

[TomPaine]

All interesting. I run my tyres as per the handbook at 35 all round.

Unless you run the car on the same brand and spec of tyres it was sold with, I never think the handbook is very relevant! So it's worth checking later/different tyre manufacturers' specific recommendations, eg Michelin might be saying 36 for one spec tyre and Falken 41 for another.

[Petemate]

All interesting. I run my tyres as per the handbook at 35 all round.

Unless you run the car on the same brand and spec of tyres it was sold with, I never think the handbook is very relevant! So it's worth checking later/different tyre manufacturers' specific recommendations, eg Michelin might be saying 36 for one spec tyre and Falken 41 for another.

Thanks Tom - MOT next week, I'll have a look at the wall chart and see what it comes up with.
Pete

[Norfolk Jim]

Saab did change it later on and mine actually says 36 - 38 on the VIN plate

[sgould]

Our 9-3 runs more comfortably with higher tyre pressures.

On the 9-5 I run at around 38.  It seems to still give even wear across the tread.  I find this on the winter tyres as well, also running at 38.  But Vredestein recommend a pressure of 46 psi!!