What would happen if I keep driving on GAS(REX) w/o chargng?

[surferdudetoku]

This may be a damn question but please kindly teach me if you know. With the range extender, is it possible to drive forever as long as I fill up the gas every 30-40 miles on the way? What would happen if I keep driving without charging?

 

[Jeffj]

Yes, you can drive "forever". Several folks, primarily in Europe, have reported on multi-hundred or even thousand mile trips with the REx doing just that.

 

[WoodlandHills]

To amplify on this: you can drive "forever" as long as your state of charge does not drop to true zero. You have a cushion at the top and bottom of the battery pack and here in the USA, the REx will come on at 6% SOC, thus you theoreticaly should never run out of electricity. But throw some long hills at a car with lights and heat or a/c on and the REx cannot keep up with the load. When that happens, the REx runs flat out and the car takes power from the battery to make up the difference, eventually there is nothing left in the battery and you are reduced to creeping along at 6 mph until you reach the summit and the draw is reduced.

To avoid this the i3 was designed to have the REx come on at 75% so that there is a much larger battery "cushion" before complete depletion. The real world effect is that you never run out of battery on a long trip since the REx can catch back up when the road flattens out. This capability was traded away in NA to CARB in exchange for valuable Carbon Credits although it is possible to restore full control. The issue is somewhat controversial since cars in non-CARB states as well as all of Canada are included in this arrangement too.

 

[surferdudetoku]

Thank you so much for the information! Very helpful!!!!!!!

 

[danwat1234]

There are people in the Facebook "BMW i3" closed group that have hacked the car to allow hold mode for the USA Rex, not to mention, the gas tank really physically is 2.4 gallons, not 1.9 gallons (not 100% verified info tho). It's just software that limits how much of the tank can be utilized.

https://www.facebook.com/groups/BMWi3/permalink/716676611739536/
gas tank;
https://www.facebook.com/groups/BMWi3/777315069009023/?notif_t=group_comment_follow
and
http://www.bimmerfest.com/forums/showthread.php?t=821072 (let me know MODs if you don't like linking to other forums)

 

[Kathy Mendoza]

What if the gas is not used. Does it turn to varnish like gas in a lawn mower that is left too long?

 

[SSi3]

What if the gas is not used. Does it turn to varnish like gas in a lawn mower that is left too long?

The fuel system is pressurized on the i3 REx to help prevent this very thing... prolongs the fuel much longer than a regular gas car. This is why you have to press a button in the cabin to release the fuel filler door, it takes a few seconds to de-pressurize the system and allow the flap/cap to be opened.

 

[martinj]

My experience is that in the 3.5 years of ownership, I have never used the Rex, It self maintains every 2 months for 10 minutes. I have put about 2 litres of fuel in over this period to keep the tank full and so far so good.

 

[johnheddy]

When I bought my used 2017 I3 Rex in PA, the dealer coded it for me so that the hold state of charge at 75% was available and pressing programmable button 8 turned on hold state of charge if below 75%. I regularly drive 320 miles each way from PA to MA every month (640 miles round trip.

I fill up the 2.4 gallon gas tank (when truly empty, it does take 2.3 to 2.4 gallons to fill). Fill up two about 2.3 gallon cans and put them in the Frunk, and start with 100% user SOC State Of Charge. This is actually about 90% true SOC. As soon as I reach 75% SOC, I press 8, and the REX turns on. I run until it is nearly dry and pull over and add gas before it stops. If you wait for it to run dry, you lose a little SOC each time and eventually you have to stop and charge. When you start back up after filling the tank, the setpoint SOC marker changes to what it is when you press 8 (hold SOC mode), so your setpoint gets lower for each stop. Even stopping before the REX runs dry loses some SOC as the car is programmed NOT to increase the SOC above where you pressed the hold state of charge button. If you drive over 65 or up a mountain, you fall behind on charge and make it up coming down the other side or by driving slower. If you run 80 for an extended period, you slowly lose more and more of your buffer, but the setpoint doesn't move. If you drive slower for the last few miles before filling up you can build back to the point you started with, or close to it. But your mileage will be worse, as your gas is both driving the wheels and charging the battery, so plan on fewer miles per gallon when doing this.

I think BMW did that to optimize fuel economy. You lose efficiency charging and discharging the battery vs directly powering the motor. I just wish there was a way to tell the car to sit there and turn gasoline into battery charge for instances like a power outage where you can't charge and are already at low SOC.

The slow creep down of SOC setpoint could also be fixed if you could refill the tank on the drive (like transferring from a second tank), or just had a bigger tank. A 10 gallon tank would make the i3 a sweet little plug in hybrid that could go all electric for up to 120 miles in summer or 70 in temperatures around 10 F, but you could just hop in and fill the tank and drive from coast to coast like a regular ICE car without having to spend 30 min each 100 miles to charge.

If I am driving home where I have a level 2 charger, I save some gas and finish off on electric because I know I have a charger waiting for me. If I am driving to MA, I do the opposite and try to save electric range and use gas, as I don't know when I will be able to charge next, or if electricity will cost more than gas there. Generally the hotel to office distance is short, and I can last 5 days on a full charge, so getting a partial charge for free even a 110V 10A trickle charge on a regular basis slowly builds the SOC back up during the trip, and I don't need to use gas while there, or while at home, just for the long trips between them.

 

[ksnax]

Anything more than 2.1 gallons put into the REx tank on a refill IS AN OVERFILL. Total tank capacity is "2.38 gallons" according to BMW including the 0.5 gallons as reserve. 2017+ cars use the same tank size and are defaulted to 0.28 gallons of reserve. Following that, coding really only unlocks 0.2 gallons usable from the system volume of 2.38, as there is no way to draw the remaining 0.28 gallons reliably without running the pump dry.

So while one can put more into the tank, either by using a can or bypassing the automatic pump shutoff, that is utilizing the filler neck for storage and increases potential risk of dumping fuel into the vapor recovery canister. I think a lot of us are getting away with it by a thin margin, but 2.1 is the intended useable design limit of the system regardless of year and or coding, and where the pump should be stopping.

I stick to filling no more than 2 gallons in the can I use (it's max rating) because it's a lot of extra work or expense to drain the evaporative canister for so little potential gain.

 

[johnheddy]

For people who have had the check engine light and been told they destroyed the evap canister by over filling the tank... Have you pulled the OBD codes and checked what is really happening? There is a problem with corrosion on the temp/pressure sensor for the tank, and when it fails, you have to drop the tank and remove the evap chamber to get to that sensor to replace it. If they convince you that you damaged the evap chamber, they can charge you for the labor to replace it and while they have the tank out (evap canister is bolted to the tank) they can easily fix the real problem which often is the corroded pressure/temp sensor. There is a note out to automatically replace that sensor if you are performing other service that leaves it accessible. I don't think they are encouraged to drop the tank and replace it for free if that is the only issue. The new model sensor is gold plated to prevent the corrosion from re-occurring.

 

[johnheddy]

Also, when I first started driving, I was letting the REX run until it shut down due to lack of fuel before refilling (lost some SOC in the process) and I was able to pour a 2.3 gallon gas container into the tank without it over filling and running out the neck. My second container is 2.5 gallons and it will overfill the tank if you are not careful. Sometimes I fill it first and use the pump to only put 2.3 gallons into it to avoid overflow.

 

[accidentalyEV]

When my 2021 I3s with 31,000 miles Rex actually works without shutting off and throwing a drive train error and check engine light it works well. I have been told the REX is not designed for primary propulsion and will likely die an early death if used too much. I agree with many people posting on this forum in that DO NOT OVERFILL THE GAS.....It will be very bad for you