Aircon fuel economy

For the last two tankfuls, every time I've taken the car out it's been raining. When it rains, I switch the blower to feet & windscreen, fan position 1, and aircon on. Stops everything misting up.

And for the last two tankfuls I've experienced a noticeable drop in fuel economy. For a while I thought something was up but could it really just be my constant use of aircon? With the driving style I've been using I should see about 180miles by half a tank and I'm getting 150... Thoughts please

-Ian

It will be the air con im fairly sure of it. Have you heard the difference it makes to the idle rev when you switch it on and off??

180 miles for half a tank? that's damn good, or is yours a UK spec Ian?

it could well be the use of the air con i suppose although i have to admit i don't usually see a huge drop when i use mine (although admittedly it's in short bursts rather than constant usage).

switching my aircon on at idle raises the rpm by approx 200 - and i get a noticeable drop in performance. Doesn't seem the most efficient system TBH but it does do the job! I also drop around 40 miles per tank so maybe this is the norm?

10% fuel efficiency drop they say mate,ive noticed it as well.

(sorry,couldn't resist)

180 miles for half a tank? that's damn good, or is yours a UK spec Ian?

J-spec T67 - big turbo's driven at normal speeds = better MPG because there is no turbo down low...+ the manifold and turbo have a better VE than the stock system.

J-spec T67 - big turbo's driven at normal speeds = better MPG because there is no turbo down low...+ the manifold and turbo have a better VE than the stock system.

Mine must be seriously overfueling then. I only get 200 miles to a full tank driving very economically...without air con on.

Junk the SAFC and get an EMU mapped

Mine must be seriously overfueling then. I only get 200 miles to a full tank driving very economically...without air con on.

J-spec T67 - big turbo's driven at normal speeds = better MPG because there is no turbo down low...+ the manifold and turbo have a better VE than the stock system.

mine is an n/a and i'm lucky to see 150 to half a tank

i think a new O2 sensor is in order

Junk the SAFC and get an EMU mapped

Its on the shopping list for prob next summer. Will it really make that much of a difference (Sorry for the thread hijack).

mine is an n/a and i'm lucky to see 150 to half a tank

 

i think a new O2 sensor is in order

NA = high compression...

A big single set up will will do about 27mpg on cruise.

NA = high compression...

 

A big single set up will will do about 27mpg on cruise.

god dammit

Junk the SAFC and get an EMU mapped

I easily get 260-270 miles to the tank, 70% London City driving The rest is either motorway or the occational blast.

And I do have an Apexi SAFC.

I easily get 260-270 miles to the tank, 70% London City driving The rest is either motorway or the occational blast.

 

And I do have an Apexi SAFC.

But are you on larger injectors and a single turbo?

I've not really noticed- but most of my commute is on the motorway, I guess if you are doing a lot of stop-start or waiting at lights then it'll be worse as the idle rises by 200rpm.

Er, right, wow, this got busy while I was away

OK so it looks like my use of the aircon is what's doing it. That's cool as the only other option was a fuel leak as I know it's not running too rich under acceleration or cruise (AFR gauge for the win).

Yep, turning the aircon on raises the idle. It also drops again when the compressor disengages - it doesn't actually constantly run it, I think it's off for about half the time it's on. I had the aircon on, the lights on, the rear demister, and it was running the cold start cycle, I didn't use the accelerator for half a mile the revs were that high Oh, and the aircon compressor is declutched if you go wide open throttle so it shouldn't affect performance under those conditions

It's a J-spec tank, so 70 litres. I've squeaked 300 miles out of a tank, but the needle was on the last line (about 7 litres left) and my retina was burnt from the orange warning light. That was a good steady motorway cruise at 90mph as well, with some boostage. As Alex said, the VE of these engines goes up by about 3mpg when you junk the stock hotside bits and replace them with a big turbo and tubular manifold. You could use that to sell the conversion to your other half you know.

-Ian

You could use that to sell the conversion to your other half you know.

You are a friendly and helpful person

Can the same thinking be used to convince a bank manager

So to cut a long story short what kind of mileage should i expect out of my N/A auto from a full tank ?

I can't survive without aircon most of the year

I can knock 5mpg off my average by using aircon constantly.

Ian, its about time you started getting shitty mileage like the rest of us

u should count yourself lucky to get 150 from half a tank.

mind you, i prob use my turbo timer too much

My N/A will get anything between 260 - 300 miles on a full tank and the needle can get to the bottom line of the 'E' before there's nowt left in the tank...

I get 300 miles + 90% of the time