Toyota Corolla 1.8L Fuel Consumption

[Hiro]

O2 sensors? Technically there's only one, in the exhaust, but if it is faulty then it can definitely lead to the engine chewing fuel (what a lot of people also call an O2 or oxygen sensor is the intake air-temp sensor, but this measures temperature only and has only a small effect on fuel consumption). Have you tried pulling error codes? You'll need to go for a drive in test-mode to really check the O2 sensor out, as it could be an intermittent thing or only when under load. Also, is it auto or manual? Obviously autos have worse fuel consumption than manuals, but if the transmission isn't locking the torque converter or not shifting into 4th/overdrive when it should then you could simply be using more fuel because the engine is working harder.

As for the size of the tank, it is indeed a 50L tank, however like a lot of Toyotas the fuel gauge (and low fuel light) is quite pessimistic - the light will initially come on when you have about 12-15L left in the tank, and stay on when you have about 10L - I know several people who get extremely paranoid and fill up at the nearest servo the instant the light comes on, not realising that you can go for upwards of 100km further and still not run out. The most I have ever put into the tank is about 47L, although that was so low that it was starving the fuel pump going around a roundabout and up a hill, something I would very much not like to experience again. Since I know my car well and am rarely far from a servo though, I tend to fill up around 43-45L.

[Hikaru Sorano]

Question to you Hiro.

Do you know which would be the symptoms of a faulty temp sensor in the gas mileage or at the moment of starting cold / hot? Could the sensor affect it?

Cheers

AB

Edited February 26, 2012 by Hikaru Sorano

[Hiro]

Question to you Hiro.

Do you know which would be the symptoms of a faulty temp sensor in the gas mileage or at the moment of starting cold / hot? Could the sensor affect it?

Cheers

AB

Which temp sensor? Intake air or coolant? The intake air-temp sensor is purely used to fine-tune the fuel-injection, as the density of air changes with it's temperature - however the full range of the sensor only accounts for a relatively small change in density, so even a faulty sensor won't stuff things up too much (and certainly wouldn't affect starting). Coolant temp sensor on the other hand will determine whether the engine is cold or hot which can make a big difference in starting - if the sensor is faulty and saying that the engine is warm then the ECU and idle-up won't go into cold-start maps and the engine will quite likely struggle to start. If the sensor is stuck in a cold reading then the ECU will constantly think that the engine is cold and add extra fuel (as it does on cold-start) which can significantly increase fuel consumption - think of it as a choke on an old carbie car; it helps starting when cold but makes the car run rich when warm, chewing through fuel. You can get similar problems with a thermostat that is stuck open, although in saying that my thermostat was on its way out for quite a while (and the engine would never get up to temperature unless it was idling in traffic) and my fuel consumption was barely effected (6.5-6.7L/100km on the roadtrip up to Brisbane for last year's TOCAU annual meet)

[Hikaru Sorano]

Yeah, I meant the coolant temp sensor. And you answered my question, thanks!

Cheers

AB

[camrolla]

O2 sensors? Technically there's only one, in the exhaust, but if it is faulty then it can definitely lead to the engine chewing fuel (what a lot of people also call an O2 or oxygen sensor is the intake air-temp sensor, but this measures temperature only and has only a small effect on fuel consumption). Have you tried pulling error codes? You'll need to go for a drive in test-mode to really check the O2 sensor out, as it could be an intermittent thing or only when under load. Also, is it auto or manual? Obviously autos have worse fuel consumption than manuals, but if the transmission isn't locking the torque converter or not shifting into 4th/overdrive when it should then you could simply be using more fuel because the engine is working harder.

As for the size of the tank, it is indeed a 50L tank, however like a lot of Toyotas the fuel gauge (and low fuel light) is quite pessimistic - the light will initially come on when you have about 12-15L left in the tank, and stay on when you have about 10L - I know several people who get extremely paranoid and fill up at the nearest servo the instant the light comes on, not realising that you can go for upwards of 100km further and still not run out. The most I have ever put into the tank is about 47L, although that was so low that it was starving the fuel pump going around a roundabout and up a hill, something I would very much not like to experience again. Since I know my car well and am rarely far from a servo though, I tend to fill up around 43-45L.

Thanks for the prompt reply.

I too thought that there's only one O2 sensor. I can see one connected right on the manifold... would that be the one?

Sorry I haven't tried pulling error codes...

It's an Auto... it hits 4th after 80kmph... I think it was you that told me the torque converter was kicking in at this stage... rpm drops to 2000...

Thanks again

Camrolla

[Hiro]

The only O2 sensor is on the engine pipe, if you've still got stock headers then it'll be just after the exhaust manifold-engine pipe flange and the heat shield - if you look down into your engine bay you'll see the sensor and the wiring sticking out towards the radiator, the wiring should run up towards the radiator fan. Be careful taking it off as you don't want to round the nuts off, like any exhaust component it will have gone through a lot of heat cycles so be wary of snapping the studs too. If they are too tight then try heating the nuts up with a butane torch or the like, and use a breaker bar for extra leverage.

And 2000rpm @ 80km/h sounds a little low if anything, the manuals are geared to be doing ~3200rpm @ 110km/h, but then again the autos could be geared a little taller.

[camrolla]

Just hit over 400 kms on the tank today... but that was because I did about 100km highway milage... better results but not the best. Not what I'm after :(

Regards,

Camrolla