Audi A4 B6 1.9 TDi poor fuel economy !

**Morgaine** · 17-02-2013,05:22 PM

Did changing the stat help with the problem? I have noticed with my A6 2.5 TDI quattro that it's doing somewhere in the region of 20mpg and that it runs very cold. The temperature barely moves unless I'm sat in traffic. I've not had it very long and had other things to fix (ABS ECU and a fuel leak!) which took priority but now looking at the fuel consumption. Given the low running temperature it sounds as if the thermostat could definitely be the culprit?

**Google44** · 17-02-2013,06:53 PM

When I changed mine it did improve consumption. However, still not brilliant. I've had so far bottle of Redex in and tried another MAF. None seems to improve it. Get about 42 on motorway. If you look on my other thread I am seeking advice on how to diagnose the fault (if any) using VCDS.

**Stefan Paiu** · 18-02-2013,06:22 PM

I've changed both the CTS and thermostat on friday. Now it gets to 90 deg C in about 10 mins. The fuel economy is still not great but there's only 5 miles to work so I didn't really have a chance to test it properly. I've driven today in quite heavy traffic and I got about 27 MPG, which still seems low.
Now my problem is that I've put about 3 litres of coolant and I've looked today and it's dropped about half centimetre again. I suspect it's either leaking from the thermostat or the system needed a bit more. Another problem is that it gets really hot inside the car and I've noticed today that the passenger side blows hot air even if i set it on low. Driver side is fine, although it still seems warmer than before.

Bottom line, I've changed the CTS and thermostat so the temp stays to 90c, but still no great effect. What's next, MAF sensor?

**kite** · 18-02-2013,06:27 PM

If your heater blows hot when set to cold you may have an air flap motor not working correctly.
Scan the car for faults.

I wish I could tpye...

**red40red** · 21-02-2013,04:31 AM

hi, I've been having the same problem. I've read that the camshafts wear and thats the cause. Sorry it's bad news, but hopefully it's just a sensor (for both of us!).

**Alfonzo** · 21-02-2013,10:04 AM

Camshaft wear? That's interesting. Are there any other tell tale signs or ways of determining if they are worn excessively?

**adamss24** · 21-02-2013,11:04 AM

Yyou need to take the rocker cover off and inspect the cam lobes for wear, there are hundreds of pictures of worn cams on line...

**Alfonzo** · 21-02-2013,11:27 AM

Originally Posted by adamss24

Yyou need to take the rocker cover off and inspect the cam lobes for wear, there are hundreds of pictures of worn cams on line...

Cheers. Hundreds of pictures eh? Ha Ha! That's never encouraging

**Autobulbs** · 21-02-2013,01:22 PM

There seems to be a lot of really bad ideas about low low rpm giving good fuel, you need to drive to the torque curve of the car with gentle acceleration. Driving at extremely low RPM strains the engine and will be adding more fuel than gentle acceleration with the torque curve of the car. Straining the engine will also 'coke' it up quicker and it leads me to believe you may have a few minor problems dropping your MPG. A good french tune up once and a while is good for your car (full throttle high revs) Check your filters are clear as said, has your oil been changed? And a serious one check your tyre pressures are all correct and your alignment is also correct these are very important.

Let us know how it goes.

**Doctle Odd** · 21-02-2013,01:29 PM

Can I suggest a pint of petrol to half a tank or so once a month. All the stuff below is true give her some clog every so often it's fun

Originally Posted by Autobulbs

There seems to be a lot of really bad ideas about low low rpm giving good fuel, you need to drive to the torque curve of the car with gentle acceleration. Driving at extremely low RPM strains the engine and will be adding more fuel than gentle acceleration with the torque curve of the car. Straining the engine will also 'coke' it up quicker and it leads me to believe you may have a few minor problems dropping your MPG. A good french tune up once and a while is good for your car (full throttle high revs) Check your filters are clear as said, has your oil been changed? And a serious one check your tyre pressures are all correct and your alignment is also correct these are very important.

Let us know how it goes.