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xreyuk

Original Poster:

592 posts

25 months

[news] 
Wednesday 13th June 2012 quote quote all
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.

It's also returning on average 10mpg higher in urban driving when started warm, as opposed to being brought up to temperature and the trip reset

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'. The car is under warranty so without an error code or some sort of evidence I don't know how far I'll get.

Thanks guys

xreyuk

Original Poster:

592 posts

25 months

[news] 
Wednesday 13th June 2012 quote quote all
Nobody? frown

JimbobVFR

697 posts

24 months

[news] 
Thursday 14th June 2012 quote quote all
How long does it take to get to temperature and is it stable at that temperature (on my E36 this exactly 12 o'clock on the guage)

McSam

5,359 posts

55 months

[news] 
Thursday 14th June 2012 quote quote all
Sounds interesting. I don't have any immediate ideas about what's causing it, but since it is seemingly dependent on the conditions under which the ignition is switched on, it would seem the ECU is screwing something up. Obviously, it should constantly adapt its fuel strategy based on the actual situation, rather than just what temperature it was at when it was first started, so whether it's a sensor issue or something else, it looks like electronic control.

It sounds like, whether or not this is possible, a sensor the ECU relies on is sending only the reading it takes at the point the ignition is turned on, and then never updates the whole time the engine is left running. That would explain why stopping and restarting at operating temperature seems to "cure" it.

While you say it feels down on power as well, it's worth checking (read: obtaining hard numbers to prove it's not a placebo effort you're getting) the power delivery under both conditions too. If you haven't completely lost the will to live with it yet, I'd recommend doing the same sort of test again, but this time doing some nice long in-gear accelerations. 30-70 in third, 40-80 in fifth, something that tests the entire rev range but is also long enough that small inaccuracies in your timing don't make much difference. If you fancy doing it at even higher speeds then that's good because these are even more dependent on power output.

Main reasons I'm thinking that are a) it can give us a vague percentage peak power loss, and b) it proves there is actually something wrong rather than it simply being the trip computer fudging a reading.

davepoth

22,593 posts

79 months

[news] 
Thursday 14th June 2012 quote quote all
Before ripping out the ECU, I'd suggest changing the thermostat.
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xreyuk

Original Poster:

592 posts

25 months

[news] 
Thursday 14th June 2012 quote quote all
Thanks for the responses guys.

It takes around 5-6 miles to heat up on the morning run to work in current temperatures. About 3 1/2 miles of that is 50mph, the rest is normal urban driving in 30mph zones.

McSam, I have Vag Com so can take any readings, which readings would you suggest I take and then drive like you said? I'm sure it's not a placebo effect, but no harm in proving it. It's mostly around acceleration I feel the difference in power when I drive the car as I normally do, I.e accelerating to approx 2,500rpm and then changing gear (which drops me to about 1,500rpm in the next gear, any lower than that and the engine feels sluggish)

As for changing the thermostat, I can't, the car is under warranty and the reason im asking on here is so that I can try and nudge the dealer in the right direction, or if possible, obtain proof by collecting logs as stated above.

It's also strange in that turning it back on again immediately after turning off doesnt seem to cure the problem, it needs to sit for a few minutes at full temperature with the engine off.

I would have thought I was dodgy computer readings, but the loss of power and also the lack movement of the fuel gauge over long journeys when the engine has been restarted leads me to believe its genuine. My trip also underestimates by about 2mpg over a whole tank. I.e indicates 55mpg when hand calculated I've done 57mpg.

Edited by xreyuk on Thursday 14th June 12:13

McSam

5,359 posts

55 months

[news] 
Thursday 14th June 2012 quote quote all
Definitely not suggesting an ECU replacement, like I said, it seems far more likely to me that it's just receiving a dodgy sensor reading!

I noticed you said you had VAG-COM, I'm not familiar with the use of it myself though I know a few people who are. I think your best bet for finding a very definite area to look at is posting this in the VAG forum on here, with the car model and year in the title as well - Tame Tech is the guy you're after, he seems to be the oracle with things like this smile

Are thermostats on these here modern cars connected to any electronics? Because if not I doubt it's going to be that. The thermostat would be to blame if the car took excessively long to warm up, or gradually lost temperature at a steady speed, but neither of those problems exist here. It's not so odd that the engine needs to be off for a short period before restarting to fix the fault, as a lot of systems won't reset immediately as soon as it's turned off. Saves everything recalibrating if you stall in traffic.

I would definitely take a stopwatch out and do some in-gear acceleration timing under the two conditions, because this is much better proof for a dealer. They must get all sorts of lemons in saying "it's down on power" when in fact they're full of rubbish, but if you can get some serious disparity in the times your car achieves then that's a much more serious warranty case. With something like this, if they can't find an error code, they'll tend to assume there's nothing wrong - you can prove otherwise.

I quite believe that it is a real fault, but was just pointing out how the dealer might consider it! Fuel economy is an extremely sensitive thing, in-gear acceleration far less so. Of course, if you do find a huge difference in the times, you could always take one of SEAT's mechanics out and prove it in front of them!

I'll be keeping an eye on this one smile

FoundOnRoadside

436 posts

24 months

[news] 
Thursday 14th June 2012 quote quote all
5-6 miles seems a long time. My Astra (1.7CDTI) is pumping out heat from the vents in half a mile, and any of the modern diesel work cars (Focus 1.6TDCI, Corsa 1.3CDTI, Mondeo 2.0TDCI) are up to temp before I get out of town to the motorway which is less than 2 miles of free flowing traffic.

Certainly looks like a stuck open thermostat that's not letting the lump heat up, so you're stuck on the rich running warmup cycle.

Ozzie Osmond

15,576 posts

126 months

[news] 
Thursday 14th June 2012 quote quote all
How are you "measuring" this mpg? If you're looking at some dash computer readout then don't kid yourself that's what the car is actually doing! The ONLY way to check mpg is brim-to-brim tankfulls. Even then, there is the accuracy (or otherwise) of your odometer to take into account, especially if the car is running on non-standard wheels or tyres.

StottyZr

4,650 posts

43 months

[news] 
Thursday 14th June 2012 quote quote all
FoundOnRoadside said:
5-6 miles seems a long time. My Astra (1.7CDTI) is pumping out heat from the vents in half a mile, and any of the modern diesel work cars (Focus 1.6TDCI, Corsa 1.3CDTI, Mondeo 2.0TDCI) are up to temp before I get out of town to the motorway which is less than 2 miles of free flowing traffic.

Certainly looks like a stuck open thermostat that's not letting the lump heat up, so you're stuck on the rich running warmup cycle.
This seems most likely. Could be worth pressuring Seat.

rotarymazda

284 posts

45 months

[news] 
Thursday 14th June 2012 quote quote all
How about taking it to a dyno and getting proper power measurements before/after warm restart.

StottyZr

4,650 posts

43 months

[news] 
Thursday 14th June 2012 quote quote all
rotarymazda said:
How about taking it to a dyno and getting proper power measurements before/after warm restart.
Rotarymazda? I bet you saw the title and thought "yes, thats me"

getmecoat

Sorry, its bad joke day over here.

Captain Muppet

7,715 posts

145 months

[news] 
Thursday 14th June 2012 quote quote all
JimbobVFR said:
How long does it take to get to temperature and is it stable at that temperature (on my E36 this exactly 12 o'clock on the guage)
Some gauges on modern cars are for indication only, and will sit at the "this is OK" position unless it's really cold or really hot.

xreyuk

Original Poster:

592 posts

25 months

[news] 
Thursday 14th June 2012 quote quote all
Thanks for the information guys.

I didn't realise 5-6 miles was a long time to warm up, I'd been told that this was the norm by a few people on the Briskoda forums, and the guy from Seat told me his takes 15 minutes to warm up. I'm tempted to exaggerate when I next take it into Seat just to try and get them to change the thermostat, but as usual, no error code = no problem, although I've seen plenty of examples of a dodgy thermostat without error codes.

I have been measuring tanks brim to brim, and found that the trip computer under calculates by about 2 mpg, so I'm getting better mpg than it's indicating. Taking that into account, I doubt it's faulty when showing 52.4mpg for one journey, then 65mpg for the same journey.

I was wondering whether the gauge on the dash could be giving false information, I can monitor coolant temperature with vag com and do a start and see how it goes from there.

I can monitor a lot of stuff from Vag Com so anything that might help with the diagnosis of power can be logged. I've posted this in the VW marque forums to see if anyone looks there.


xreyuk

Original Poster:

592 posts

25 months

[news] 
Thursday 14th June 2012 quote quote all
Any other information would be helpful too smile

otolith

23,764 posts

84 months

[news] 
Thursday 14th June 2012 quote quote all
xreyuk said:
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.
Possibly because the displayed mpg is a moving average and gets reset when you restart the engine, so one figure includes a cold start and the other doesn't?

The Wookie

9,849 posts

108 months

[news] 
Thursday 14th June 2012 quote quote all
I wouldn't have thought 5-6 miles is excessive for warm-up on a diesel depending on your commute, although it has to be said it does sound like a stuck thermostat that's releasing when it's heat soaking up to a higher temperature.

Can you look at live sensor readings on the VAGCOM? Might be worth looking at the engine's temperature sensor for a start, then perhaps stuff like MAF and Lambda readings. Basically, look for odd readings such as something that's clearly out of range, a reading that's too constant to be realistic, or something that's bouncing around excessively. A lazy garage wouldn't have checked it.

Sam.F

1,051 posts

80 months

[news] 
Thursday 14th June 2012 quote quote all
OP, where did you do the motorway MPG "test?" it's worth thinking about unless you live somewhere very flat as potentially the test was rather flawed - for example if one drives from Carlisle to Penrith on the M6 you are effectively going uphill most of the way (90-100m elevation difference) whereas doing the same journey in the opposite direction you are mostly going downhill, my car will return an indicated 38mpg heading south but doing the same trip in the other direction at the same speed the OBC shows 42mpg.

Locke

1,267 posts

64 months

[news] 
Thursday 14th June 2012 quote quote all
Sam.F said:
OP, where did you do the motorway MPG "test?" it's worth thinking about unless you live somewhere very flat as potentially the test was rather flawed - for example if one drives from Carlisle to Penrith on the M6 you are effectively going uphill most of the way (90-100m elevation difference) whereas doing the same journey in the opposite direction you are mostly going downhill, my car will return an indicated 38mpg heading south but doing the same trip in the other direction at the same speed the OBC shows 42mpg.
This is true, you can get very different mpg from going different directions on the motorway. You need to do the same stretch of motorway in the same direction for it to be a fair(er) test. Try also do it at night if you can when there is no traffic about. I bet its a really annoying this problem. Seat won't want to know. I can imagine how you feel.

McSam

5,359 posts

55 months

[news] 
Thursday 14th June 2012 quote quote all
People need to read the OP properly, he tested the car properly - in both directions of the same stretch of motorway in the same hour for each condition, and reset the MPG readout himself each time once rolling at a constant speed. A very good test, actually.
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