Any real limit to running REX?

[yebar16037]

Chuffed to have found a great i3 (2017 REX) today and will be picking it up on Tuesday. It cost me not much more than half what it would have cost 18 months ago.

When I test-drove it, the battery flattened and the range extender kicked in. I’ve not driven one with the REX running before and I was surprised at how unproblematic it was.

Does anybody routinely drive long distances (say >400 miles) relying mostly on the range extender? I know it’s not the anticipated use, but I’m wondering whether there’s any particular reason not to.

 

[SSi3]

Congrats on the new ride!

To answer your question, technically you can drive on the REX all you want however it wasn't really meant for that and doesn't get all that great of fuel econ for being such a tiny engine. It's also not the most reliable little thing but that's proven to be completely random across all the model years as some people report bulletproof reliability for thousands of miles/kms whereas others (like me) had nothing but problems with the REX from day one. My experience with the 2015 I had steered me away from ever getting another REX as it was that bad.

 

[louisgrenier]

We have to understand its limit to drive on the REX for 400 miles. The first limit is the power of the REX. The power of the REX is able to furnish enough energy on flat ground with no headwind at around 90 km/h. So if we are going up a long slope, or if we drive at 110 km/h, we will consume more electricity than what REX is able to furnish.

Meaning that at one point we will won't be able to sustain that speed or slope.

As an example, if the REX starts at 6% of the battery remaining, we will see the battery going down from 6% at that speed or slope. The available energy is the addition of what is left in the battery, plus what the REX is able to furnish.

How can we do it? Well, if we have the hack ( North America) or the European menu to start the REX at 75%, then it gives us a lot of reserves to slowly use until we are stuck at a lower speed or slope. Starting the REX at 75%, or even 25%, will give us a lot of room ( mileage at a speed or slope ) until the battery is too empty to sustain the desired speed, slope, or acceleration. If we do not have the menu to start the REX at 75% or less, then we have to limit our speed, slope, and acceleration to what the REX is able to furnish as energy.

The other limit is Ethanol poisoned fuel. If we are in a country that mandates a lot of Ethanol in the fuel, we will have from time to time some problems with the REX. I don't know about the latest version, but the first years REX and its fuel system did not like ethanol. I am in Canada, and tried to use the highest octane from Petro. Had a lot of problems. This high-octane fuel has a good percentage of ethanol, so they have to mix a lot of additives to achieve high octane rating. Looks to me that these additives make the fuel less stable when sitting for a month or two. The REX and its fuel system didn't like it. When i switched to Shell ethanol-free fuel, I didn't have a problem from this moment. Now it is no more available since a few months, so i will continue with Shell and see what happens with their new ethanol-mixed fuel. My remarks on fuel is not really pertinent to your question about the limit of using the REX on a trip. The first part is more relevant, the part about adjusting your speed and slope to sustain what the REX is able to furnish vs the reserve of battery before the REX starts

The REX is not able to sustain a battery level for slope or higher speed than 90 km/h. we have to manage our energy reserve to consumption: reserve in the battery plus what the REX is able to give

 

[alohart]

I am in Canada, and tried to use the highest octane from Petro. Had a lot of problems. This high-octane fuel has a good percentage of ethanol, so they have to mix a lot of additives to achieve high octane rating.

Pure ethanol has a North American octane rating of 113, so adding ethanol to gasoline increases the octane rating of gasoline. No additives would be needed to increase the high octane rating. Maybe there are additives that are added to a gasoline-ethanol mixture for other reasons and that cause REx engine problems.

 

[agzand]

There is no hard limit, but my personal opinion is that the REX works pretty hard in the i3. In its original purpose in the 650 scooter it has much easier life and can do high mileage. But in the i3 it is probably designed for something like 20 thousand miles. That is still plenty of use as a range extender, but not much as the main propulsion unit.

Also using the REX often (like couple of times a month) will improve its life and reliability. Having it sit months at a time will result in reliability problems that people report.

 

[Davidsi3]

A slightly 'oblique' reply to the topic.

I have a 2018 i3 Rex bought about 18 months ago through 'BMW Approved Used' at about 18,000 miles. It now is up to 27,000 miles, and so far, so good - I'm delighted!

My (UK) experience with the little Rex engine has been entirely positive. I chose that option as a first step into electric car ownership - ie I have a 'safety net'. Initially, I used the Rex engine quite frequently, but as I became 'braver', less and less, and this is where I discovered that the car itself noticed! Every 3 or 4 weeks, it advises that due to lack of use, it's going to switch to petrol and run its own 'Maintenance Cycle'. It does this for about 10 mins to warm up thoroughly, then switches back to battery! Very clever.

I fill the 9 litre tank with Shell V-Power which has cleaning additives and whatever else. Unlike regular petrol (10%) V-Power only has 5% ethanol, and I use it in my 2CV too! The little engine is very unobtrusive, and 'putters' along nicely, switching in and out seamlessly, and of course, it's ability to add up to 100 miles to a journey is invaluable.

My own angle to the question was, how can I find out how many miles the petrol engine itself has 'driven' in its life? Anyone?

 

[mojo]

Because of the way that the REx is decoupled from the wheels, it seems unlikely that its total use could be expressed in miles. There are situations where the petrol engine contributes only part of the energy while driving (i.e. the battery is still discharging, even with input from the REx) and there will be others where it contributes more.

So I suspect that the best you could hope for is the total runtime of the engine. In theory the total number of revolutions could be logged, but I doubt they bother.

If the rest of the "driver experience" is anything to go by, it's unlikely that BMW would have made this data visible to the owner anywhere, so you would probably need a diagnostic tool such as BimmerLink to access the data, if it's available at all.