Low gas mileage, thermostat stuck open?

[loginatnine]

Hi all!

It's pretty cold these day where I live (about 2 weeks of -20C and lower). I know that winter can affect gas mileage but right now, I'm averaging about 13l/km (18mpg). I believe this is not normal.

I just bought the car and I noticed that the engine temp looks low to me (see pic attached). Is it supposed to run this cool? I also went to the garage and he checked with a obd2 scanner and nothing was wrong. Could a stuck thermostat be the cause of my poor gas mileage?

Thanks

[PLP]

it could, but your temp looks just fine. It could be little higher, but I know that they are not so accurate. With one set of gauges I had it about same as you, but with another (KIA changed instrument cluster on my Rondo) it is almost touching the middle point.
Only ScnaGauge could tell me what the real temperature was: +82C.

However, I did notice that Elantra is very sensitive. When I stop at the lights, the temp will start going down (from +82C to +75C) if about -10C outside and blower on 2-3.
This in turn increases idle RPM from 650 at +82C to 770 or more at +75C - so you see more fuel...

However, you might test it - start the car when after it was sitting for an hour or so, eventually in the morning (but it will take more time) and start comparing temperature of the upper and lower hoses (in and out for radiator/engine).
If they get warm before your gauge travels near "the just below middle point" your thermostat is bad.

If the upper suddenly gets hot near the operating temperature on the gauge, it means the thermostat just opened.


Yes, cold temp can affect gas consumption and, depending on how you drive and if the car can get to operating temperature, it greatly impacts short commutes.


And I hope you meant 13l/100 km... which is kind of high as for days when we had -18 to -10 I got about 8-9l/100 km on my about 15 km daily commute in light city traffic.
Summer I can get as low as 6.0, and sometimes even below that...

[loginatnine]

Originally Posted by PLP

it could, but your temp looks just fine. It could be little higher, but I know that they are not so accurate. With one set of gauges I had it about same as you, but with another (KIA changed instrument cluster on my Rondo) it is almost touching the middle point.
Only ScnaGauge could tell me what the real temperature was: +82C.

However, I did notice that Elantra is very sensitive. When I stop at the lights, the temp will start going down (from +82C to +75C) if about -10C outside and blower on 2-3.
This in turn increases idle RPM from 650 at +82C to 770 or more at +75C - so you see more fuel...

However, you might test it - start the car when after it was sitting for an hour or so, eventually in the morning (but it will take more time) and start comparing temperature of the upper and lower hoses (in and out for radiator/engine).
If they get warm before your gauge travels near "the just below middle point" your thermostat is bad.

If the upper suddenly gets hot near the operating temperature on the gauge, it means the thermostat just opened.


Yes, cold temp can affect gas consumption and, depending on how you drive and if the car can get to operating temperature, it greatly impacts short commutes.


And I hope you meant 13l/100 km... which is kind of high as for days when we had -18 to -10 I got about 8-9l/100 km on my about 15 km daily commute in light city traffic.
Summer I can get as low as 6.0, and sometimes even below that...

Oups sorry I meant 13l/100km!

I'm waiting on my obd2 scanner, it should be here this week so I will update the post.

It's an automatic transmission and I drive VERY carefully but it's usually short distances (less than 10km). Still, 13l/100km is way too much even for that!

[PLP]

Originally Posted by loginatnine

Oups sorry I meant 13l/100km!

just like I assumed.

Originally Posted by loginatnine

It's an automatic transmission and I drive VERY carefully but it's usually short distances (less than 10km). Still, 13l/100km is way too much even for that!

nope, not necessarily.
I drive 16 km a day. It is very mild city traffic. With M/T I can get about 9l/100 km with outside temp being -16C.
The engine reaches operating temp at about 7-8 km or so. I do not let it idle before I start driving.
During the first 8 km I get about 11l/100 km. Then it drops very quickly due to engine being hot to reach final 8-9l/100km.

The same route can be done with result of as low as 5.5-6.0l/100 km IF the engine is hot to start with. Otherwise I can get 6.2-6.5 l/100km.


So, 10 km at -20C... yes, 13l/100 km may be reasonable. Plus it is automatic. You can't really get engine braking (when injectors are shut off) because transmission fluid is cold. Plus the shifts are elevated due to the cold conditions.

Check tires pressure, brakes - maybe some extra dragging forces increase your fuel use.

[loginatnine]

nope, not necessarily.
I drive 16 km a day. It is very mild city traffic. With M/T I can get about 9l/100 km with outside temp being -16C.
The engine reaches operating temp at about 7-8 km or so. I do not let it idle before I start driving.
During the first 8 km I get about 11l/100 km. Then it drops very quickly due to engine being hot to reach final 8-9l/100km.

The same route can be done with result of as low as 5.5-6.0l/100 km IF the engine is hot to start with. Otherwise I can get 6.2-6.5 l/100km.


So, 10 km at -20C... yes, 13l/100 km may be reasonable. Plus it is automatic. You can't really get engine braking (when injectors are shut off) because transmission fluid is cold. Plus the shifts are elevated due to the cold conditions.

Check tires pressure, brakes - maybe some extra dragging forces increase your fuel use.

Tires pressure A1 and so are the brakes.

I've received my OBDII scanner and I installed the torque app on my phone. Here is one log I made yesterday at -10C :
Log

Everything looks in order except the O2 sensor 2 equivalence ratio that is missing, is that normal? I think I'm getting a voltage out of it I'm pretty sure. There is a sudden temperature drop in the coolant temperature at around 16:54 that also look odd to me.

What else could I log to try to see if there is something wrong?

[PLP]

Based on Litres Per 100 Kilometer(Long Term Average)(l/100km) this is not the full log.
However, when speed was steady (26 m/s) fuel use was normal. You got some harder accelerations, but nothing extraordinary.
Fuel use at steady speed is about 4.6-6.8 L/100 km - that is good.

Keep in mind the device is not accurate - in both my Elantras (XD and HD) the info from ECU was off by as much as 15% - it was reading low.

Anyway, what I see is that you loose energy on braking. In 20s you loose 8 m/s - that is a lot from 22 m/s to 14 m/s. That is braking, not coasting - energy waste.




As for the readings from O2 sensor - no, it is OK to not read when it is cold. Why it does not read when you stop - I do not know.

Temperature drop - not, that is normal. Take a look - you were coasting. No load to the engine so it was cooling off. Thermostat was still slightly open so it let more cool water in... and the temp did not drop below 78C. I see it all the time. On winter with blower on 3 I can drop as low as 70 while coasting from 90 km/h down to 50 km/h

[loginatnine]

Originally Posted by PLP

Based on Litres Per 100 Kilometer(Long Term Average)(l/100km) this is not the full log.

You are correct, it is not the full log, it breaks down logs individually for each trip (I got a bunch of them). Here are all the logs from that day, first one is a hard cold start (car didn't move for 24h), the 2nd one is a start after a 1h30 stop from a hot engine (that's the log file from the other post) and the last one is after a 5h30 stop.
Hard cold start
Cold start after 1h30 stop at -10C from hot engine
Cold start after ~5h30 stop

As for the O2 sensor, it's my fault I had made some calculations in the column and I uploaded the wrong version. The correct version is included in the links up here (it's the 2nd one). It is only showing the "-" character and no numbers at all.

Anything else I can check? Would it be a good idea to try to replace the O2 sensors even if their readings looks ok?

Thanks for your help btw!

[PLP]

first thing I see here is a lot of idling... overall almost 3 minutes.
The worst are idling on cold - look on engine temp (-3C) and fuel flow rates ( more than 75 ml/min avg) - it was over one minute.

Then again, almost 1.5 minute when engine was 36C, flow rates 40 ml/min.

Just those two will give you 125 ml of petrol wasted. That 125 ml can drive your car for more than 2 km on highway.

Does it matter? Try, the whole trip is 16 minutes. Average is... say 9 l/100km. If you get 10 km... you used 0.9 l of petrol.
So, if it was 775 (not 900) at 10 km you would get 7.75 not 9.0 l/100 km...

[syncro87]

An article on the subject I thought you might find interesting. Note the part about your tires having more drag at lower temps than at higher temps, and the effect of air temp on air density-- i.e. aerodynamics.

Why is the fuel economy of an automobile worse in the winter than in the summer?: Scientific American

[loginatnine]

Originally Posted by PLP

first thing I see here is a lot of idling... overall almost 3 minutes.
The worst are idling on cold - look on engine temp (-3C) and fuel flow rates ( more than 75 ml/min avg) - it was over one minute.

Then again, almost 1.5 minute when engine was 36C, flow rates 40 ml/min.

Just those two will give you 125 ml of petrol wasted. That 125 ml can drive your car for more than 2 km on highway.

Does it matter? Try, the whole trip is 16 minutes. Average is... say 9 l/100km. If you get 10 km... you used 0.9 l of petrol.
So, if it was 775 (not 900) at 10 km you would get 7.75 not 9.0 l/100 km...

Yea you're right that on short trip, cold idling is the worst. It was probably a traffic light, I don't let it idle for nothing.

I'm just a bit deceived by it, I had a corolla before this car and it was totaled. On the exact same short commutes, I averaged 7.5l/100km max in winter. Granted it was a M/T and a 1.8L but still. I expected my fuel mileage to go up, just not that much.

I'm still gonna run tests and report here if I find anything. Thanks for your help, if you have any ideas, let me know!