SEAT Leon - Low power and poor mpg.

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Wed 13 Jun 2012 21:45
SEAT Leon - Low power and poor mpg. - xreyuk




Since I bought my Seat Leon 1.6TDI CR, I have been having varying fuel consumption results. I was told to adapt my driving style, and that has certain helped, however, I definitely think there is a problem with the car.

The problem I've noticed, is if I start the engine from cold, and let it get up to temperature, it NEVER reaches full efficiency, and it feels like an engine with 80BHP instead of 105BHP.

If I then stop for around 10-15 minutes, and turn the engine back on (whilst it's still warm), the MPG takes a massive jump up, especially on the live data display. The power also feels like it should. This is how I would have thought the car would perform all of the time.

I decided to do a test. I started the engine cold, got it up to temperature and went to the motorway nearby. I reset the trip when I reached 70mph, and stuck cruise control on. I did a 10 mile journey to the end of the motorway, made a note of the reading, and then did the exact same thing back up the other side (waiting until 70mph to reset the trip etc). I averaged the two readings. at 52.9mpg.

I then stopped the engine for 20 minutes, got a cup of tea etc. I then did the exact same test on the exact same bit of motorway. The average mpg this time around was 65.4mpg. A MASSIVE jump.

Around town I noticed an mpg jump of about 10 mpg from when the engine is started cold and brought up to temperature compared to when started warm.

All the mpg readings have been done when the engine is up to temperature, there is no warm up period included in any figures.

Do you have any idea what could be causing this? Someone on another forum said they noticed similar symptoms in a Mondeo with a faulty temperature sensor/thermostat. I've also read that it could be the MAF.

I have fully activated VAG COM, so if anyone could suggest anything I could be maybe monitor to take to SEAT, because, as usual, I'm just getting the old 'we're not having an issue when we drive it'.

Thanks guys



Edited by xreyuk on 13/06/2012 at 21:47

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Wed 13 Jun 2012 22:07
SEAT Leon - Low power and poor mpg. - Peter.N.

It could well be a faulty sensor but I noticed while I was in Scotland a few weeks ago, when the ambient temperature was very low, nearly freezing in fact when we arrived my 406 Hdi was struggling to reach 60mpg (I drive very carefully) when after a few days the temperature shot up to 25C my fuel consumption improved to 67.3 mpg but this was only gained on a long run with a continiously hot engine at about 60 mph or less.

When we left the cottage with a cold engine the consumption was in the low 50s until normal temperature was reached, then it was giving just over 60 mpg on a cold day and 65+ on a hot one. This took from 5-15 minutes according to the ambient temperature.

The efficiency of common rail engines means that in cold weather being driven gently they may not reach normal operating temperature, if yours doesn't do this in warm weather you my have a faulty thermostst.

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Thu 14 Jun 2012 12:17
SEAT Leon - Low power and poor mpg. - dieselnut

I'm fairly sure this engine will have a DPF fitted & wouldn't be surprised if it wasn't at the root of your problem. The car should be doing considerably better MPG at 70 than you quote. Do you normally make a lot of short journeys, this will clog the DPF which will then try to force a regen & waste fuel. I have recently changed from a 1.9 PD Passat to a 2l CR & both would easily beat you figures even though it is a heavier car. I have noticed that the CR engine uses more fuel during warm-up ( it tries to heat the DPF quikly so wastes fuel doing so ) but onece up to temperature is about 10% more fuel effiient than the PD engine.

As you have VCDS you can check all the engine parameters inluding engine temperature & lots of info about the DPF. Go to the Ross-Tech site to find which measuring blocks to monitor.

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Fri 15 Jun 2012 03:10
SEAT Leon - Low power and poor mpg. - xreyuk
Hi

I do mostly motorway miles, not a lot of stuff around town, it's been 400km since my last regen according to VCDS.

I'm going to try monitoring as many temperatures as I can, as well as the MAF on startup and see what happens.

Does anyone think it could be anything else?
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