Civicic

Have a 2013 civic ex auto, 78000km (48k miles). Getting lousy 18mpg (12.5 l/100km) city. No error codes.

Did a compression test: 200-180-180-189 psi. Guessing about 20% compression loss, premature wear. Would that explain lousy fuel consumption? What would a new new engine get for compression test?

ezone

No IMO.

How long have you had this car?

Is this economy drop something new, even though driving habits have not changed? What was your fuel economy last year at this same time?

Is this fuel economy number what you see on the info display, and what is that display set to show for fuel economy? (when is trip meter programmed to reset, because this resets the mpg)
Is it what's been calculated by hand for each and every full tank of gas?

Even a perfect running car can get still net very low MPG depending on conditions and driving habits.

Civicic

Thanks fir the reply. I just bought the car in mid September. I'm comparing it to a 2001 Nissan Sentra this car is replacing; same driving habits. As well as the published 28mpg city driving.

Is the computer inaccurate? One trip odometer is reset at fill up the other keeps going. I understand that driving very short trips can worsen the mileage beyond the expected 28 mpg, but the difference is huge. The coloured bars on the speedometer are blue 100% of the time.

If an engine has lost some compression than I would think some of that energy is not pushing the pistons; and therefore lost efficiency.

ezone

No comparison.
The car is new to you, you get to discover everything from scratch.

Does it have LRR tires on it now?

That's only a rating, never a guarantee (read the fine print). Your driving habits are probably nothing like the govt test parameters.
My daily work commute may net anywhere from low 20s mpg in the winter to high 20s in the summer.

Fill the tank. Air up the tires.
Get out on the highway and go steady 55 mph (whats that about 90 kmh?) for about 300 miles, steady speed no slowing or stopping for the entire time.
You could see well above the 38 (39?) highway rating, that should verify the car is capable of good fuel economy, if driven appropriately.
I have seen over 50 mpg in my own car.

Close enough on my car, but to know you should calculate by hand and you'd need to do it every time to see if the average over several tanks is still close to what the display shows. MPG calculated from a single tank fill is not reliable info due to variables
There's a whole lot more involved than short trips.
If you put the shifter in d3 instead of D they will stay blue all the time. Additionally, I think the feature can be turned off and on in the IMID menus (check owners manual), see if it's been disabled by the previous owner
Right now I don't think that's your problem.
FWIW you don't have misfire codes so the compression isn't enough of an issue to upset the PCM.

I expect to see 180+ psi whenever I check comp.

Civicic

Comparing it to the previous car with all other things being equal is a good comparison. The 2013 civic is more fuel efficient than a 2001 Sentra. You can also compare with other owners at fuelly.com.

The tires are the original oem hankook tires, a little overinflated, a little old so lowered rolling resistance.

All the cars I've owned have been reasonably close to published ratings.

Did a manual calculation and it's the same as the computer. The computer seems accurate.

The best I've seen with this car is 25mpg highway, which is much worse than other drivers are getting mixed highway/city.

I would expect to see 210+ psi compression on this engine, maybe 215+. The specs have a minimum as low as 130psi. So you shouldn't see misfire codes due to compression unless it's very low but that doesn't mean it hasn't lost efficiency.