Questions from a new XC90 owner

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HI All

I have recently purchased a 2018 XC90 D5. Its an R design pro and so far I am loving it. I do have a couple of questions for the wealth of knowledge on this forum.

1. Engine Hiss - With all of the windows up, the car is almost silent and there is very little engine noise. With the windows down I can hear a pronounced hiss under acceleration. I am not sure if this is a normal sound or if there is some gasses escaping from somewhere.
2. MPG - over the last 100 miles (mix of town and motorway) I have averaged 27.9mpg. I am hardly a saint when it comes to the accelerator but I have not been going crazy either and while this is a 2.7 ton car I was expecting better MPG. Is this in line with what others are finding?
3. Vibration through the accelerator - I had the opportunity to hit 80mph on a private road recently and while the car itself was very smooth, I did notice that there was a slight vibration coming through the accelerator pedal. The car itself had no vibrations, just the pedal. Is this to be expected?

Thanks in advance

[Lexman8]

Engine Hiss - Could be a leak in the PowerPulse system; a known problem area.

MPG - Long term I've averaged 34.7 mpg.

Vibration through the accelerator - Not heard of that before.

[Deman77]

After 20k break in you should be comfortably in 30s mpg.
27mpg I was before engine broke in and lots of short trips and town use. Liberal right foot. So it is not right.
I just did 39mpg airport trip half way round m25 with six people, 8 suitcases and a roof box. Mine is loaded with extras (air suspension, heater, sunroof) so as heavy as they get.
Tyres are 35-36.
And mine is pre powerpulse. Powerpulse should be even better around town and better average.
Check tyre pressure is not too low but otherwise it’s odd.

Not heard of accelerator vibrations - I went as high as 146mph on autobahn and it is very stable car at speed - 80 is nothing for it. But if it is at higher speeds you are getting it I would look at tyre balancing. I do road force balancing on mine every time I swap summer/winter. Also check for uneven tyre wear - could be indicative of geometry problems.

Just a thought - you are not confusing lane assist vibrations?

[Nicon]

Thanks for the responses.

I actually turned the lane assist function off as it was annoying me so its not that. I am going to get the wheels balanced at the weekend to see if that sorts the vibration issue and have a longer motorway drive after that so will see if that improves the MPG.

Thanks again.

[weemark]

mpg should be way better than that - over 25k or so miles I've averaged (my calculation) 36.2mpg and live in hilly Mid-Wales. Early morning drive down to Slimbridge last week (88 miles with lot of stop/start etc) gave me 41.5 indicated with 38.7 on way back

Hiss most likely Powerpulse, a common failure - offending pipe back right of the engine bay - seem to recall seeing a pic posted recently showing u what to look for but can't remember which thread this was in

EDIT - pics in this thread https://www.volvoforums.org.uk/showthread.php?t=308553

[Cmjs]

Having had several powerpluse pipe failures one way in which I check it is working is by the Hiss noise I can hear when I pull away from a junction with the window down. A working powerpluse does seem to make a noise. When my pipes have blown I have no noise.