Poor MPG

vklexer

Member
Greetings,
New member here with not so much knowledge about this car.
2001 TDI 1.4 75HP.

The car drives good, but it has poor mpg. It's around 30 MPG~. 12,5 KM in 1 Liter diesel.

Things i've done and things i know that impacts mpg.
I have 185/65r15 winter tires on it.
Changed Air filter, Oil filter, Oil. Didn't change the fuel filter.
Coolant temp sender is "shortened" because of "corrosion/contacts rusted".
Webasto is working.

What should I do to get this car to a better mpg? I'm driving quite calmly. Car is driven mostly in the city to work. I don't go over 2400 rpm that often. Usually i drive it between 1500/2000.
Any help is appreciated
 

motosport

Member
Well, first thing to do is getting the coolant temp sensor replaced/fixed, otherwise it will always run in cold mode, meaning a much richer mixture while its waiting for the engine to come up to proper operating temperature. And when the engine management system never gets signal from the coolant temp sensor, it will keep running very rich.. Its an easy and cheap fix, so give that a go..

Alex
 

depronman

A2OC Donor
Well, first thing to do is getting the coolant temp sensor replaced/fixed, otherwise it will always run in cold mode, meaning a much richer mixture while its waiting for the engine to come up to proper operating temperature. And when the engine management system never gets signal from the coolant temp sensor, it will keep running very rich.. Its an easy and cheap fix, so give that a go..

Alex
Seconded - the water temp sensor is one of the most critical inputs to the ECO in respect to fuel economy. There are 8 fuelling maps in the ECU and a controlling map tells the ECU which of the fuelling maps to use. The Controlling map uses the engine water temperature input. The fuelling map for 0 deg C injects almost twice the fuel per stroke compared to the 90Deg C fuelling map.
Therefore you can see where your poor fuel economy is coming from

Cheers,
 

vklexer

Member
Had a chat about this with my friend that fixes this car and it looks that I've mistaken coolant temp sensor with a sensor thats responsible for coolant amount. It used to show its low, even tho it was full.
Any other ideas? :x
 

depronman

A2OC Donor
Does the temp gauge on the dashboard read 90 Deg C (middle of the gauge) ?
Even if it does the ECU may be getting a different temperature reading as the temperature sender mounted in the engine as two circuits, one feeds the dashboard gauge and the other the ECU.
A scan of the engine control units blocks will show you what temperature is being reported into the ECU. If the thermostat is working correctly and ambient temperature is not less than 0 Deg C and webasto is working the car should be up to, or around, 90 Deg C after about 8 miles of running at around 2000 / 2500 RPM. The heater should feel to be blowing hot.
If either the gauge or the ECU is not reading around 90 Deg C AND the heater is blowing hot then the engine temperature sender is the most likely cause. If the Heater is blowing cool then the thermostat is the most likely, and if you are really unlucky then it could be both :)
 

vklexer

Member
When I bought the car, I knew that Webasto wasn't working. The coolant temp was always on 60. So we checked it with vag. We connected somewhere where it showed rpm and engine temp. Vag showed Temps slowly rising and that way we came to conclusion that the temp sender was working, but needed a lot more driving to get it at least a bit near the working temp. 70 was max without Webasto. When I fixed Webasto, coolant gauge shows 90 after a short trip, so I guess everything is OK with this sensor. Is this the right way to check the ecu measurements?
 

Peter

Member
You seem to be mixing gauge temp (G2 sensor) and ECU temp (G62 sensor). The G2 temperature is "processed" and the gauge will show 90 degrees almost all of the time. Only the G62 temperature is relevant to the engine and affects your MPG.

A simple bluetooth dongle (ELM327) in the OBD port and a free app on your smartphone (Torque lite) allows you to permanently monitor the temperature reported by the G62 sensor to the ECU. If this temperature does not rise beyond 70 degrees, as you suggest to have experienced with VAGCOM connected, your thermostat needs replacing.
 

vklexer

Member
I'll just try to simplify what i'm talking about. I don't have much knowledge about cars, but here goes.
Dash board temp gauge (i guess the coolant) is working. It shows 90 degrees and stays there.
We've checked before if the dash board temp gauge is seen by connecting VAG and it matched the readings on the computer with the readings on the dash board.
By doing that, did i check the thing you are talking about?
 

Ian210

A2OC Donor
Interesting comments. My temp gauge never shows more than 90 and I did think of fitting a hotter thermostat, as diesels like to run hot. My passat, Honda and T5, have all run between 95 and 110. Where is the G62 fitted and would it be worth just replacing it at 100k to make sure the ecu is getting the correct signal? I drive very carefully, yet only get mid 50s mpg.
 

JIGSAW

Banned
Interesting comments. My temp gauge never shows more than 90 and I did think of fitting a hotter thermostat, as diesels like to run hot. My passat, Honda and T5, have all run between 95 and 110. Where is the G62 fitted and would it be worth just replacing it at 100k to make sure the ecu is getting the correct signal? I drive very carefully, yet only get mid 50s mpg.
The only issue would be if the temp gauge does not get to 90 where it should sit on our A2 TDI's, if its sitting lower at 60 after 5 to 10 miles id say its more than likely the thermostat not opening , this also makes the ecu over fuel due to it thinks the engines running cold, theres also 2 temp senders, one up beside the cylinder head under the vacume pump and one on the lower N/S rad pipe and these have caused problems for other members

if i were getting poor mpg the first things id change are the air filter and fuel filter if these have not been replaced recently as it will make a huge difference on mpg if these are over due
 

Peter

Member
In my TDI 90 the gauge (G2) hardly moved and there was an error logged in VCDS (I did an auto scan during my test drive before I bought the car).
The first thing I did was check the heater (warm) and the actual engine temperature as seen by the ECU (G62). That was around 80 degrees, a bit cold but stable.

The G2 and G62 sensor sit in a single (green) housing with 4 pins, see picture.
sensor.png

Do not mistake the G2 and the gauge for the actual engine temperature. The engine temperature may vary between 80 and 100 degrees and the gauge will still show 90 degrees.

The G2/G62-sensor is a bit hidden behind a small plate that supports some cabling. This is looking at the left hand (curb side in UK) side of the engine (mine is a LHD, hence the brake fluid reservoir in the picture)
DSCN2307.JPG

Once removed (one 10 mm nut) you can see the sensor (or rather the black connector sitting on top).
DSCN2324.JPG

I replaced the sensor last week and my gauge, after a cold start, takes 5 miles to start moving from the 60 mark, creeps to 90 degrees and doesn't move anymore after 10 miles.

I'll replace the thermostat shortly and expect the G62 temperature to rise to about 90 degrees and MPG to improve a bit.
 
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vklexer

Member
Thank you for all your responses. I hope you'll stick around to help me narrow down the problem.
Can someone give me instruction on how to check what temps does my ECU see using VAG cable?
Since my friend has that cheapo VAG, I'll try using that if its possible. If not, i'll try buying that Bluetooth connector which was mentioned before
 

Peter

Member
In VCDS the G62 temperature is available in several measuring blocks.

Go to
01-Engine controller
08-Measuring Blocks
select block 001
field 4 is engine temp (G62)

The ELM327 bluetooth dongle can be easily found on eBay for just a few pounds.
 
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