Hi guys

This is a strange one and I'm sure there's a simple explanation. My fuel consumption has been a little down over the past 2 months but I put this down to my MAF which is on the way out (new one has arrived just got to swap it out). 2 weeks ago the engine coolant sensor went with the temp gauge fluctuating between 60-70 and sometimes off, since the sensor went I have found my fuel consumption has improved from 5.3l/100km to 4.8l/100km which when you are doing on average a 1000km's a week adds up pretty quickly.

Does anyone have any idea why the sensor would cause the improvement? I have a new sensor on order so hope to switch both the sensor and MAF out next week hopefully consumption figures stay this good.

Cheers,

Clayton

Try a boost leak,you'll get even better mpg

Try a boost leak,you'll get even better mpg

Its going in for service in the next week or so and will ask if they can do a boost leak test at the same time.

The ecu thinks the car is cold so injects more fuel to warm it.

Hence higher fuel consumption.

The ecu thinks the car is cold so injects more fuel to warm it.

Hence higher fuel consumption.

Thats what I thought would be the case but its the opposite my fuel consumption has improved.

Yeah it wiil improve with the new sensor. As thr old one reads cold.

Yeah it wiil improve with the new sensor. As thr old one reads cold.

The new one hasn't been installed yet thats whats bizarre driving up today engine temp sat at 60, Its like the failed MAF and failed coolant sensor has been balanced by ECU to provide right amount of fuel.

When the sensor is on the way out it will read all over the place and the ecu will react to it. When it dies completely the ecu will revert to a default setting.

The sensor was probably telling the ecu it was -40 or some other random moronic value

When the sensor is on the way out it will read all over the place and the ecu will react to it. When it dies completely the ecu will revert to a default setting.

The sensor was probably telling the ecu it was -40 or some other random moronic value

That explains it probably been slowly failing the past couple of months hence the poor consumption now its completely failed the default settings are more optimum.

Yeah it sounds like your CTS has been at fault for a while then. CTS has 2 separate outputs, & I'd guess the ECU has been getting incorrect temp, & over fuelling.

I'd strongly advise that you only use genuine VAG parts when it comes to engine sensors as aftermarket usually don't work correctly or sometimes not at all.

Edited 2 June, 201313 yr by pauldazzle

Ok, I got the CTS replaced on Friday but looks like the issue persists but is different now. The temp gauge no longer fluctuates but now it seems to not go any higher than 70C. I do a 100mile round trip everyday and even pushing the car hard last night I only managed to just eek it up to 75C.

Was I unlucky and happen to get a faulty CTS or is there another underlying issue that I should be looking for maybe the thermostat?

Stuck stat or air lock.

ah never thought of air lock that's a quick one to remedy will try that first and hold thumbs it fixes it. From reading through other links the stat sounds a pain to repair.

If it is the stat, it's not that bad to swap, you just need the right tools.

Will have a read through whats needed and send my wife off with a shopping list for fathers day, can never have enough tools