Best fuel (octane) for Rex

[Deutsch100]

There is a member on the Facebook i3 group I belong to, that says using Premium fuel for the REX can easily result in a Check Engine Light.

I believe the i3 REX Owner's Manual says to use a minimum Octane rating of 89 for unleaded fuel, but 91/93 (Premium is recommended).

I will need to add fuel for the first time to my 2020 i3S REX I took delivery of in September. Since I had endless Check Engine Light issues on my 2019 i3S, and BMWNA bought my car back from me....I am super freaked out about getting a CEL.

Do you all recommend 89 Octane, 87, 91?!

Also, the Facebook group says to fill and hold the nozzle until you hear the first click and then stop filling. My BMW dealer told me to under fill REX, since it is very easy to overfill and this will result in a dealer visit and a CEL. How do you fill REX? Just hold the handle until it stops filling on its own, or purposely under fill the tank?

Thanks for all replies.

 

[Pahaska]

I let the pump click off on its own. So far, good on both I3s I have owned.

The only check engine light was when the fuel flap opened on the highway and it took me some time to get off the road and close it. I reset it and no recurrances.

 

[Deutsch100]

I let the pump click off on its own. So far, good on both I3s I have owned.

The only check engine light was when the fuel flap opened on the highway and it took me some time to get off the road and close it. I reset it and no recurrances.

Thanks Pahaska. I filled up today, since I was out. I used 91Octane Chevron, and I just filled until the pump clicked off (1.5 gallons). No CEL

 

[Timjohn]

I was recommended to fill with Chevron high test not just for the octane rating but because there is no ethanol (alcohol) contained in this grade of fuel. I guess ethanol free gas stores better.

 

[jadnashuanh]

Ethanol content will vary by where you're located. If the state is part of the CARB air quality, it will have ethanol in it. If it's not, it may not. The higher grades of gasoline generally have higher levels of detergents in them. Plus, you should check the website for whether the supplier is on the top tier approved list. https://www.toptiergas.com/ BMW and many other car manufacturers recommend only using fuel from those listed on that site.

FWIW, as fuel is stored, it starts to lose some of its octane boosters, so starting out higher, especially on the REx that may not use it up for awhile, is a good idea. Worst case, if it does contain ethanol, is you get what is referred to as phase separation, and that can cause some nasty effects. I'd consider using a fuel stabilizer in it unless I regularly ran the REx.

 

[Deutsch100]

I was recommended to fill with Chevron high test not just for the octane rating but because there is no ethanol (alcohol) contained in this grade of fuel. I guess ethanol free gas stores better.

BMW, Mercedes, RR, Bentley and even years ago SAAB told me to only use Chevron. Maybe it's silly, but I have used Chevron since 1995.

 

[Deutsch100]

Ethanol content will vary by where you're located. If the state is part of the CARB air quality, it will have ethanol in it. If it's not, it may not. The higher grades of gasoline generally have higher levels of detergents in them. Plus, you should check the website for whether the supplier is on the top tier approved list. https://www.toptiergas.com/ BMW and many other car manufacturers recommend only using fuel from those listed on that site.

FWIW, as fuel is stored, it starts to lose some of its octane boosters, so starting out higher, especially on the REx that may not use it up for awhile, is a good idea. Worst case, if it does contain ethanol, is you get what is referred to as phase separation, and that can cause some nasty effects. I'd consider using a fuel stabilizer in it unless I regularly ran the REx.

In my 2019 Rex and now my 2020 Rex, I add a wee bit of fuel stabilizer to the tank. Just a bit of insurance, in my mind. With my 2019, I asked my Service Advisor at BMW, and to my surprise....he said adding some is a good idea!

 

[jadnashuanh]

I bought an X5 45e hybrid in September - have used about 1/8th tank of fuel in it so far. If I keep going like I am, I may not need to buy any fuel for it for 4-5 more months as most of my driving is well within its EV capabilities. I might consider putting some fuel stabilizer in it, too. Where I live, you can't buy fuel without ethanol in it unless you want to pay at least double, and then, since that stuff isn't taxed, it is essentially illegal to use in a road vehicle.

Using unleaded without ethanol in it should result in better efficiency, as ethanol is 10% or so less efficient by volume, but since it's only 10% of the total, the hit is smaller.

 

[Deutsch100]

I bought an X5 45e hybrid in September - have used about 1/8th tank of fuel in it so far. If I keep going like I am, I may not need to buy any fuel for it for 4-5 more months as most of my driving is well within its EV capabilities. I might consider putting some fuel stabilizer in it, too. Where I live, you can't buy fuel without ethanol in it unless you want to pay at least double, and then, since that stuff isn't taxed, it is essentially illegal to use in a road vehicle.

Using unleaded without ethanol in it should result in better efficiency, as ethanol is 10% or so less efficient by volume, but since it's only 10% of the total, the hit is smaller.

I would add some fuel stabilizer. Cheap & easy insurance, especially against ethanol "damage".

 

[3pete]

Do you all recommend 89 Octane, 87, 91?!

As a BEV owner, I don't settle for anything less than 110 or 120, and even those are only for when I can't find 240... (volts of course)! :lol:

But seriously, if you're filling up a 2 gallon tank once a month, it's a lot easier to splurge on "premium" gas or higher octanes rather than a 17 gallon tank once a week for a gas vehicle. You might be wasting that money but as long as it's not contra-indicated by the manufacturer, it probably won't hurt and is probably even cheaper insurance than it would be for an ICE.

On the third hand, about 90% of the people who have told me to "only use XXXXX gas" had extremely incorrect reasonings for it (eg. "My uncle was a mechanic for Ford and said I should only run my Corolla on 91 octane or it'll explode") and I'm now suspicious of any recommendation to that effect. The small tank and infrequent use of the i3's engine seem to be legitimate reasons to potentially be more finicky on gas though.

 

[Deutsch100]

Do you all recommend 89 Octane, 87, 91?!

As a BEV owner, I don't settle for anything less than 110 or 120, and even those are only for when I can't find 240... (volts of course)! :lol:

But seriously, if you're filling up a 2 gallon tank once a month, it's a lot easier to splurge on "premium" gas or higher octanes rather than a 17 gallon tank once a week for a gas vehicle. You might be wasting that money but as long as it's not contra-indicated by the manufacturer, it probably won't hurt and is probably even cheaper insurance than it would be for an ICE.

On the third hand, about 90% of the people who have told me to "only use XXXXX gas" had extremely incorrect reasonings for it (eg. "My uncle was a mechanic for Ford and said I should only run my Corolla on 91 octane or it'll explode") and I'm now suspicious of any recommendation to that effect. The small tank and infrequent use of the i3's engine seem to be legitimate reasons to potentially be more finicky on gas though.

I agree, with only 2 gallons needed for the i3...use the best.