Any real limit to running REX?

[alohart]

In reality, whether BEV or REx suits you better depends on your circumstances and, to an extent, your location. I've owned my 120Ah BEV for more than 18 months now, and I've never had a situation where I would have needed to use the REx engine - so for my circumstances it would simply be a waste - weight carried around everywhere without any useful purpose.

Exactly our situation. For over a decade, we have used our i3's for what BMW designed them, to be a megacity vehicle. We've never road-tripped them, so a REx would have been a waste. I am very happy to be done with ICE maintenance and problems.

 

[louisgrenier]

You can go to a small airport and buy 100ll (low lead) they don't allow corn lcker in aviation fuel yet. Good stuff for small engines that sit a lot like lawnmowers in the great white North

Are you sure the Rex does not have a catalyser? I use 100LL on everything i can that does not have a catalyser. Like my generator, old cars, even mixed in chainsaw, but i never tried in the Rex because i was thinking it have a catalyser. I would surely use 100LL if it does not have a catalyser

 

[louisgrenier]

You can go to a

 

[mojo]

Are you sure the Rex does not have a catalyser?

The REx engine does have a catalytic converter. "An air-gap-insulated exhaust manifold enables the catalytic converter near the engine to heat up quickly through minimal heat losses."

 

[Whereitis]

I find the Rex to be the only thing that prevents extreme anxiety every time I go more than 10 or 15 miles in a day in the i3. My 14 Rex typically shows about 60 e-miles in the summer but only about 40 in the winter, and with the heat on and if I drive the slightest bit aggressively (which I tend to do a lot), that winter e-range quickly drops to 25 or less. Yes it's a 10 year old car and the HV battery has obviously degraded some, but even on short trips, I often find the e-range down to single digits by the time I get home. With the Rex, I just don't care. So what if I need to put half a gallon in it the next day? Without the Rex, I would never be able to stand the stress of wondering when I'll be stranded with zero charge. Just my own experience.

 

[unL33T]

Because of the way that the REx is decoupled from the wheels, it seems unlikely that its total use could be expressed in miles.

I was playing around with an OBD reader the other day and there was indeed a reading for mileage on the REx. Mine said just over 11000 km. The car has 117000 km on it. There was also a running hours reading for the REx but I can't remember what that one said.

To answer the original question, most I have done is 300 km each way. I had to fill up ~4 times each direction and hold the brake while I got out to fill while the car was running. The car gets very poor fuel economy on the REx. 9-10L/100km. I keep 3x5L jerry cans in the frunk so occasionally I just lock the brake with a modified clamp/expander and dump in a whole can.

 

[I3drivei3]

I was playing around with an OBD reader the other day and there was indeed a reading for mileage on the REx. Mine said just over 11000 km. The car has 117000 km on it. There was also a running hours reading for the REx but I can't remember what that one said.

To answer the original question, most I have done is 300 km each way. I had to fill up ~4 times each direction and hold the brake while I got out to fill while the car was running. The car gets very poor fuel economy on the REx. 9-10L/100km. I keep 3x5L jerry cans in the frunk so occasionally I just lock the brake with a modified clamp/expander and dump in a whole can.

May I ask why you lock the brake while refueling? I am assuming this keeps the car "on" and allows you to see something that you couldn't see with the car off. Thanks.

 

[mojo]

I was playing around with an OBD reader the other day and there was indeed a reading for mileage on the REx. Mine said just over 11000 km. The car has 117000 km on it.

It does make you wonder how they could calculate that - given that the REx engine can be running while the car is stopped? Maybe they have some algorithm that does a calculation based on the total number of revolutions and the total runtime, or number of revolutions and distance traveled while the REx is running? There's zero chance of finding out - not something that BMW is ever likely to document for a mere owner...

 

[unL33T]

May I ask why you lock the brake while refueling? I am assuming this keeps the car "on" and allows you to see something that you couldn't see with the car off. Thanks.

Otherwise the car turns off which resets your Hold State of Charge setting to whatever your current charge is instead of whatever it was when you first enabled it. The car loses about 3% of battery per 10 km at highway speed even with the REx running. It will also keep charging with the REx until you are within 3% of the original SoC if you hold the brake.

 

[Whereitis]

I was playing around with an OBD reader the other day and there was indeed a reading for mileage on the REx. Mine said just over 11000 km. The car has 117000 km on it. There was also a running hours reading for the REx but I can't remember what that one said.

To answer the original question, most I have done is 300 km each way. I had to fill up ~4 times each direction and hold the brake while I got out to fill while the car was running. The car gets very poor fuel economy on the REx. 9-10L/100km. I keep 3x5L jerry cans in the frunk so occasionally I just lock the brake with a modified clamp/expander and dump in a whole can.

It surprises me to see you got such poor Rex fuel economy. I tested this when I first got the car. Starting out with a full 2-gallon tank and the HV battery already reading zero e-miles available, I went for a 120-mile round trip mostly on the highway, with the Rex running the entire time of course. It required two refills during the drive (the one after I was almost home for just over a gallon), and I calculated it was getting about 38mpg purely on Rex. Based on your numbers, you got about 24mpg (10L = 2.64G & 100k = 62m), considerably less. Have you done this again to confirm your mileage?

 

[Mustrum Ridcully]

The REx engine does have a catalytic converter. "An air-gap-insulated exhaust manifold enables the catalytic converter near the engine to heat up quickly through minimal heat losses."

Are you sure the Rex does not have a catalyser? I use 100LL on everything i can that does not have a catalyser. Like my generator, old cars, even mixed in chainsaw, but i never tried in the Rex because i was thinking it have a catalyser. I would surely use 100LL if it does not have a catalyser

Hello Louis,

I apologise for the error regarding the 100LL fuel. I was unaware that the Rex had a cat when I posted that note. I am curious to know how long it would take for such a small cat to become poisoned if it ingested 3 or 4 litres of 100LL fuel, assuming you used the Rex once or twice a year.

If you reside in a state that does not mandate emissions testing (such as New England, where only Connecticut requires it), would it still be a concern if you rarely used the Rex, even if the cat were slowly being poisoned? If I owned a Rex version that I rarely used and my state did not have an emissions test, I would likely fill it with 100LL. Depending on how much a used cat on eBay would cost and how hard they are to swap, I think with a low-usage scenario, I would do the same even if the car had to pass an annual emissions test.

I have been driving my BEV 2021 i3S since last summer and have only required a charge from less than 40% on one occasion. The only time I ran it below 20% was when I took it on a long 135-mile drive in eco mode through the picturesque fall foliage in Maine.

 

[ksnax]

The biggest problem with fouled catalytic converters is structural failure of the mesh. It can literally fall to pieces within the housing and plug up the exhaust, leaving the REx unable to start or to continue operating.

Regarding economy, under controlled testing at 65F, with no AC/heat use, I logged 35MPG over multiple tanks at 60 MPH. It may be higher at slower, but it drops off quickly at higher speeds.

 

[Whereitis]

The strongest case that I've heard from others is that complexity is the enemy of reliability, and there is absolutely no doubt that the REx is more complex than the BEV.

In reality, whether BEV or REx suits you better depends on your circumstances and, to an extent, your location. I've owned my 120Ah BEV for more than 18 months now, and I've never had a situation where I would have needed to use the REx engine - so for my circumstances it would simply be a waste - weight carried around everywhere without any useful purpose.

And in the UK it's not quite as simple as it seems in the US, because the REx models were only available here with the 60 and 94Ah battery sizes - so here you have to make a compromise on battery capacity and vehicle age if you want a REx.

So, overall, it's not people grasping at straws - there are actually genuine reasons why people make the choices that they do.

I totally get your point, but you're in the UK, whereas living in the USA is in a very different situation. Even in smaller eastern states (I live in CT), I'm almost always running at the ragged limit of EV range. Even if I manage to get home without having the Rex kick in, the fact of its availability makes for tremendous peace of mind compared with wondering if I'll ever be stranded by a truly dead HV battery. Especially since I find the available range of the EV battery as indicated in the dashboard gauge is typically optimistic by 50% or more (I count on 1/2 to 2/3 at most of whatever the gauge says on any given day) and I often see the EV gauge drop to a single digit before I arrive home. I'm one who refuses to compromise the driving experience, so when it's below freezing outside as it is today, the heat stays on at 72F, and in the summer the AC runs 24/7. But I shouldn't have to drive around in a chilly (or steamy) environment just to eke out a few more miles of battery range. I also get that the Rex adds complexity to the system, but fortunately the primary additions to the car are software changes and a well-proven (and easily repaired if ever needed) gasoline engine design from a company that's been building that motor into its motorcycles for decades. I find the trade-off for that peace of mind quite reasonable.