Herman and Operation 30MPG

[WhatAmIDoing]

I recall my manual for my '98 S70 T5 saying 87 minimum octane, 91+ recommended. Key word being recommended. It will run on 87, but runs far from well. Also says 5% ethanol maximum, but most gas in the US is 10% soon to be 15%. 93 octane usually contains less ethanol, as ethanol decreases octane rating. 87 octane burns much less cleanly compared to 93, which means more deposits building up in your engine. If you spill some 87 next to some 93 on the ground, the 93 will evaporate pretty cleanly, while the 87 will almost always leave a stain.

I ran a couple tanks of 87 through my car as an experiment. Performance suffered dramatically, and as a result, so did mpg. Switching back to 93 octane resulted in a roughly 20% increase in mpg. I don't remember the exact numbers. I'll try to find where I wrote them down. If you want to hit 30mpg, you are going to need 93 octane.

Admittedly, I frequently buy 89-90 octane because I can't justify the high price tag of premium in upwards of $0.60-1.00 more per gallon compared to 87 in the U.S.

[Dave in Maine]

When you said "MAF", you lost me. What does that acronym stand for?
Thanks.

[oragex]

So thermostat is now wedged into cold mode. And now I'm going to make sure that the VVIS system is actually functional.

What am I getting now? 22mpg. All the time, day or night, highway and city.

Upcoming repairs: Thermostat

I also notice that in 'cold air' intake mode, the car will consume more fuel in winter time until the engine fully warms up. Its mostly at that moment the intake air thermostat is in fully 'warm air' mode. Even so, in winter the car takes quite a bit of warm air driving in the city, and switched to cold air on the highway. That flap works both with intake air temperature and intake air pressure (higher pressure at higher speeds). In winter, I leave mine at (about) 70% cold, 30% warm. In summer is 100 'cold' air. I put a wire on it to switch it easily without removing the whole plastic pipe.

I am surprised by your mpg numbers. For city, 22 is actually good, again it depends on how dense are the traffic lights. However, for highway 22mpg is suspect. I'd make sure the intake pipe from the the front grid to the air filter box is well in place (if the P1 has one). I've found driving the car on the highway without this duct, did abysmal mpg as the intake air must be pressurized when driving at speed (for example a CAI gets this wrong). On P2 there is a tiny hose connecting the intake manifold to the air filter box - it compares the pressure between the engine and the intake air. All this to say that the pressure of the intake air is important when driving at speed.

Checking the thermostat is very simple

One may also try to have the injectors cleaned in an ultrasonic bath (most shops for 18 wheeler have these cleaning baths)

I would also look into the transmission, it may affect mileage on highway. Some fresh oil won't hurt.

Final thoughts, did you clean the MAF the right way ? Some people confuse it with the intake temp senor. Also, on MAF only specific cleaner

My 95 sedan with the 170 HP NA manual did 27 mpg City and highway and 33 mpg on country roads.

That is extremely high mpg for city driving (assuming it's in US mpg, but even in UK mpg would be very high). This shows one very important thing: city mpg is greatly dependent on the type of city: a place with long distances between traffic lights, will get much better mpg than a place where traffic lights are at every 300m or so and not synchronized (where I live ). For this reason, mpg city numbers will always vary greatly from a city to another, not to mention about how quick does the driver accelerate from a stop.

[Rattnalle]

Orangex: it's the mpgs I got just asking Google to do a conversion. In Sweden we usually measure in litres per Swedish mile which is 10 km. So city/motorway at >100kph was, 0,84 litres/swedish mile, and country roads at <100 kph closer to 0,7. Edit: Seems to be imperial gallons. Google knows the UK is closer than the US I guess.

Gothenburg is really quite a small city with just a million people and quite spread out. If you get into it you can do a lot of coasting or engine breaking and rarely have to stand completely still as long as you avoid rush hour. Also lots of roundabouts and other crossings that don't require you to really stop most of the time. Driving around daily and making money off the difference between pay for distance driven and actual cost I got quite good at it as well.

Other than that I usually did use the entire range in second or third gear to get onto roads with a higher speed limit but then quickly got into fifth.

[abscate]

When you said "MAF", you lost me. What does that acronym stand for?
Thanks.

Mass Air Flow meter, with the meter being dropped from the acronymn

Its a gadget that measures, very precisely, how much air is flowing into your engine so that the Engine control unit (ECU) can meter the fuel precisely.

[erikv11]

It is very unusual for cleaning the MAF to actually do anything, just as it is unusual for it to get dirty. Unless the surface sensor is visibly dirty or oily, don't expect cleaning to help much.

[scot850]

Unless you read about the belief using oiled filters like K&N allows an oil film to build up on the MAF element.

Neil.

[erikv11]

I would agree with that - an oiled filter can lead to an oily MAF, in which case cleaning it may help.

[FLXC90]

With all that you have done so far, including MAF, have you done a hard ECU reset/drive modes?

Idle in park 60 sec-idle in D 60 sec.-accelerate through gears at about 1/2 throttle to 4th gear, drive for a couple miles, come to a normal, full stop.

Also, how are the O2 sensors?

[precopster]

For non turbos the compression ratio is 11 to 1 on white blocks so this is well suited to low grade fuel.

During cooler months you can get away with a mid-grade fuel on turbos but nothing less if you want to avoid detonation.