Low-ish power and mpg

[moreflaps]

Could be that while warming up you are doing 0mpg and that is averaged into your final figure. When you restart the average is reset.
HTH
Cheers

[xreyuk]

As said above (twice), I reset the trip the when the engine gets warm, there is no warmup period included in the calculations.

[moreflaps]

xreyuk said:

As said above (twice), I reset the trip the when the engine gets warm, there is no warmup period included in the calculations.

Does the trip actually reset the mpg?

Cheers

[cuprabob]

There are 2 memories for average mpg, one resets after the ignition has been switched off for a couple of hours and the other is only reset when it reaches 99hrs 59mins or 9999miles whichever occurs first.

Both memories can be reset manually by the driver.

[Contigo]

Sounds like an intermittent temp sender unit or thermostat to me. Do you really notice the lack of power? I mean you are looking at a DIS for mpg and that could easily be changed when you switch the ignition off and then on again.

A faulty temp sender/thermostat will affect the parameter sent to the ECU resulting in poorer mpg and potentially lack of power.

I had it on my B5 RS4 and it's front off job so not cheap and as I said in the other thread should ALWAYS be replaced when the cambelt is done.

[Amateurish]

Maybe the car isn't quite up to temperature on the first test? In my modern diesel, it can take a good 10-15 miles to get to fully efficient operating temperature (depending on the ambient temperature).

[xreyuk]

Thanks for the responses.

Where I live, it's a 30 minute drive to the motorway, so the engine is definitely up to temperature.

Ironically, since I monitored a start up the other day, the car has actually warmed up correctly, I don't know why or how, it's probably sods law, but I"m goign to keep monitoring it.

Is the thermostat and coolant temperature sensor the same thing or different?

Is it really a cambelt off job to change the coolant temperature sensor? If so, I'll make sure I remember just to get it changed when the cambelt is off.

At the moment however, the car is under warranty, so it's anything goes.

[Contigo]

xreyuk said:

Is the thermostat and coolant temperature sensor the same thing or different?

Is it really a cambelt off job to change the coolant temperature sensor? If so, I'll make sure I remember just to get it changed when the cambelt is off.

At the moment however, the car is under warranty, so it's anything goes.

Different devices. Thermostat controls coolant flow whereas the temp sensor unit actually sends data to the ECU which in turn controls the fuelling and on a colder engine temp will increase the fuelling.

The Temp sensor is not a cambelt off job no, it's a five minute scrape the skin off your knuckles in the engine bay to replace it or at least it was on the RS4 I had. I would start by getting them to replace and check the sensor first and then think about the Thermostat. On the Audi's the thermostat can only be changed when the cambelt is changed so it's a big job to just do it and Audi for some reason don't change the Thermostat as a matter of course when they do the cambelt!

On the SEAT it might be different so I'd do some research on a SEAT specialist forum first.

[Contigo]

You could also use VAGCOM to monitor the coolant temperature as you drive and get a log of that and compare it to the temperature gauge, some cars have oil temp and this is not what you are looking for. As these sensors are all very twitchy and vary so much, the variables are huge as to what constitutes a warm engine and it wouldn't surprise me if yours was overfuelling for the long part of your journey.

80c is probably a sound value to look at for starters and then up to 90c in slower conditions.