Ran the REX for the first time....

[Timjohn]

Hey I coded the i3 so I could run the REX at 70%. While driving in city traffic I couldn't hear it running. But from what I have read, it is quite audible but not the case with my 2020 i3S REX.

Once I reached my destination, I left the i3 on and walked to the back and I still could barely hear it. I had to place my head underneath and place my hand at the exhaust port. This confirmed it is working away. It then ran for a short period and then shut down. So I don't know what BMW did but maybe they muffled it more.

The only clue I had when it started was a pungent smell. I have experience this smell of a brand new motorcycle engine so other than that, this works wonderfully!

 

[jadnashuanh]

Running around, stop and go in a city, the maximum load normally wouldn't be all that high. The REx engine will adjust the RPM to help match the load. It's quite possible that it would run fairly slowly under those circumstances. Take it out on the highway, blast up a long grade, and your results will likely differ. But, there'd be more wind and tire noise, so you still may not hear it.

 

[JohnWasser]

The REx normally turns off when your speed is below 10 kph (unless your battery charge is below 3.5%).

One way to listen to the REx when the car is parked is to put it in the emissions test mode. The SOC has to be below 75%.

Get into the car and close the door.
Press the trunk release button
Press the Start/Stop button (BRAKE NOT PRESSED)
Press and hold the accelerator pedal.
Press and release the brake pedal.
Press and release the brake pedal again.
Press and hold the brake pedal.
Release the accelerator pedal.
Press the Start/Stop button.

The REx should start up and run at low idle.
If you press the accelerator pedal the REx switches to high idle.

The REx will stop in 20 minutes or when you press the Start/Stop button.

Be sure to get out of the car and re-close the trunk when you are done.

 

[Timjohn]

OK thanks for the routine...I will save this for future reference.

Timothy

 

[clasqm]

There seems to be a lot of variation between i3s with regard to the noise made by the REX. Mine is barely perceptible, but I've seen others complaining about the droning noise.

If the little white triangle in the charge indicator jumps from 8% to 70% (or whatever your state of charge was when you switched the REX on) then the REX is running, whether you can hear it or not.

 

[Pahaska]

I ran the range extender for the first time after buying the 2018 a month ago. I coded the car yesterday to allow it. I did not want to depend on it with 6% remaining without trying it first. Texas is a big place!

For the first 30 seconds, there was some small vibration that caused metal items in the driver's door pocket to jingle. After that, there was no vibration and I could not hear it over the radio. I ran it for the 5 miles to my take-out breakfast stop.

 

[Geodude]

I ran my REX the other day for the first time. Couldn't hear it at freeway speeds but once I started driving on a slow road (25 mph) I could hear it just barely. Kind of a light humming noise. When I parked the car and got out of it it was very noticeable as it was going through it's cycle process. The noise from the REX doesn't even bother me at all. I'm just so happy that I have the REX option on my i3. I have no "Range Anxiety" what so ever. It is nice to know that if you have to drive a bit farther than you thought or maybe forgot to charge your i3 one night that you can get to where you need to go without stopping at a public charger some place.

 

[Pahaska]

I drove the almost 20-mile round trip to San Antonio to update my I3 with the Rex running both ways. I never heard it until I stopped at a light next to a building that reflected the sound when almost home.

When I left the dealer with the newer I3, I pulled into a parking lot two blocks away from the dealer and coded the Rex to come on to maintain charge. I arrived home with about 70% charge remaining.

 

[GoldiE46]

in the city it's not bad at all, but try driving on rex for an hour at 80mph. this little thing unleashes all the possible power it has and it sounds like a combine in the middle of a corn field

 

[Pahaska]

I drove 85 miles at 70 mph from San Antonio to Austin with the REx running most of the way. I never heard it with the exception of one red light stop. Even here in Texas, I see no reason to drive 80.

 

[GoldiE46]

I guess you are lucky I've owned two and both are/were loud. Not that I am complaining, it's generator and it should be expected.

 

[jadnashuanh]

The REx rpm, and thus the general sound level, will vary considerably depending on the current SOC on the battery, and the amount of energy it thinks it needs to supply. It can go from barely at idle to its maximum speed, and the sound level will change. The vehicle also adjusts the REx some due to the speed of the vehicle in accordance with the other mentioned parameters. It's trying to keep the sound level down, so normally, will slow down as you do unless the battery level is way below where it is trying to maintain.

Probably the worst case would be when the level was below 6% SOC, and you were climbing a long grade at speed with things like the seat heaters, cabin heating, rear window defroster all going at full blast (some of those might get turned down or off by the computer in this case).

 

[Pahaska]

After living with a big exclamation point on the display and having to constantly reset a message saying the REx is due for a maintenance cycle, the REx finally ran on its own. It so happened that I had a string of days where the most I drove was to the mail pavilion and back, all of a mile and a half, and used almost no battery. This morning I had to do a 20-mile round-trip supermarket run. The REx finally fired up right on arrival at the market. I shut down rather than keep it noisily running while waiting among other cars for social-distanced delivery in the rear hatch.

The REx fired again when I restarted and ran most of the way home. The only time I heard it was when I briefly lowered a window to wave at a friend. I arrived home with 70+% battery.

 

[Steve999]

Has anyone tossed a thick blanket in the trunk to see if it dampens the REX noise a little? There doesn't seem like much sound insulation from the metal "engine hatch" to the cabin area, but I'm not sure if that's the only source. Maybe a good experiment to try (I think I'll have to dig around my closet...).

 

[Anonymous]

There doesn't seem like much sound insulation from the metal "engine hatch" to the cabin area,

The 'floor' of the cargo area that sits over the metal engine/motor cover has fairly thick sound-deadening material on the underside. I can barely hear the REx at all when it is running. Check the metal cover hold-down bolts. The cover is fastened down with bolts going through a Neoprene Nut. If they are over-tightened when the cover is replaced after an oil change, the Neoprene Nut will split, and the bolt will be just sitting held in place by the top half of the split neoprene nut, but not holding down the cover ( (ask me how I know), or the bolt will be missing entirely, either of which could make the cover loose and vibrate when the REx is on, if enough of those fasteners were compromised or missing.

 

[Pahaska]

I have never heard the REx running with windows up except once between buildings where the sound was reflected.

 

[Deutsch100]

I used my REX a couple of days ago, and when it is running on "low speed", I can barely hear it (if at all). When REX kicks into "high", then I can hear it, but it sounds like a scooter or small motorcycle outside or next to me, but it is still not loud or obnoxious inside the cabin. If I roll the windows down, you can of course hear more, but still not bad.

Oddly, my 2019 REX was a wee louder than my 2020 REX....but I think I had a "bad" 2019 in terms of sound insulations. In my 2019 the front doors rattled and the dash too and many times the moonroof covers. My 2020 actually feels like a BMW

 

[agzand]

The REX is significantly down tuned from its scooter application. In the BMW 650 scooter it makes 60 hp at 7750 rpm. In the i3 REX it makes 38 hp at 5000 rpm. So in i3 even at max rpm it is in a relatively relaxed state of operation.

 

[jakecturner]

I can barely hear mine. With the radio off, I can only really hear it when doing 80mph on the toll way. Even then, it is barely audible over the wind noise.

 

[Spamouflage]

I’ve owned my 2020 i3S for less than a month and last weekend, I went on a longer trip just so I could experience the REX. At highway speeds with the music on, I couldn’t really tell it was on once my battery hit 6%. But I was nervous because at 110 km/h, the battery charge was dropping all the way to 4% in about 10 minutes. I live in the Canadian prairies so it’s as flat as can be. By the time I was back in the city, at lower speed, I could really hear the REX a lot more. I swear I could also feel a slight vibration in the steering wheel too.

1. I wonder if long road trips at highway speeds will be possible without coding (state of charge hold).
2. The REX is an engine, so you hear it. Not annoying, but not silent either.