How often long should I run Rex?

[panamamike]

To keep Rex in good working order. I know there is a Rex maintenance cycle that will run, but is that enough?

 

[joni3s]

Yes. The maintenance cycle should be enough.

If you feel like it’s not starting/finishing, perhaps 30-60 days out maybe you let rex run.

 

[TOEd]

It is my understanding that the maintenance cycle is designed primarily to keep the injectors from clogging. Using a good quality premium fuel with a lot of detergent additives will go a long way to prevent clogging.
If you are concerned with frequency of cycle being inadequate you can use REx more often. In 4 years of ownership I have heard maintenance cycle only once. This is because we regularly use REx. No problems with REx so far.

 

[panamamike]

My guess is I'll use Rex about every 2 days, since the available range will be sort of doing a full 2nd trip to the office where I plan to charge.
Wondering if Rex for lets say 3 to 5 miles maybe 15 mins due to traffic, is ok on the engine, or if I should run it longer.

 

[TOEd]

For injectors to spray fresh gasoline a few seconds should suffice. For engine to heat up enough to dry out moisture in oil, your usage in summer (20C or warmer) should be ok (If you live in Panama, for example). However, if you run REx when temperatures are 0C or lower for prolonged periods (like in Canadian winters), you may need to run it longer imho. You will know when you change oil. If rusty water comes out before oil when you drain it, I suggest a longer run time for REx.

 

[panamamike]

For injectors to spray fresh gasoline a few seconds should suffice. For engine to heat up enough to dry out moisture in oil, your usage in summer (20C or warmer) should be ok (If you live in Panama, for example). However, if you run REx when temperatures are 0C or lower for prolonged periods (like in Canadian winters), you may need to run it longer imho. You will know when you change oil. If rusty water comes out before oil when you drain it, I suggest a longer run time for REx.

Thanks for the info. Hopefully I won't learn via rust water.

 

[jadnashuanh]

10-15 minutes should be long enough on that small engine to get things fully warmed up. If you can still see condensation streaming out the exhaust, it's not hot enough yet.

Someone will probably know, but the maintenance emissions test cycle, once that's initiated, I think, runs about 15-minutes. Keep in mind, you really want the oil temp to get above boiling and the entire exhaust to be able to end up dried out, and that can take awhile. While in an ICE, you might be able to get some cabin heat out in a mile or less, it really takes quite a long time to get fully warmed up for best operation. But, those engines are larger.

 

[3Alfas]

Somewhat related topic. With my driving habits, I don't need the REX. So, other than the maintenance cycle, it doesn't run. After two years of this pattern, a check engine light and a smell was diagnosed as bad gas. Now, every six months, I run the REX to drain the gas. ( I coded 'hold charge' for convenience.) I picked six months without any scientific facts. Is six months a good interval?

 

[i3Houston]

I picked six months without any scientific facts. Is six months a good interval?

I had issues with rex, dealership asked to run it once a month long enough that gas is recycled within 3 months. I have been practicing that for a year so far no issue except there is that feeling of guilt for polluting!

 

[Boxbrownie]

I picked six months without any scientific facts. Is six months a good interval?

I had issues with rex, dealership asked to run it once a month long enough that gas is recycled within 3 months. I have been practicing that for a year so far no issue except there is that feeling of guilt for polluting!

Just keep a minimum amount of fuel in the tank, less to go bad and less needed to add to it to keep it good, although having said that we have had the REX for 3.5 years and the only running it gets it the maintenance cycle and maybe once on a very occasional long run each year, we keep the tank usually fully topped and had no issues at all, maybe try a better fuel?

 

[Anonymous]

I keep my tank full, and add a fuel stabilizer - Pri-G Small Engine Gasoline Treatment.
PRI-G is what the military uses in fuel dumps and generators, where the fuel may be sitting for years but needs to be ready for use.

 

[jadnashuanh]

FWIW, while the fuel tank won't (or shouldn't) let vapors out, it will let air in. That air will have some moisture in it. So, to minimize condensation, you want the minimum amount of air, or, have the tank full to minimize the amount of humid air that can come in when the air cools off and shrinks.

 

[i3Houston]

I picked six months without any scientific facts. Is six months a good interval?

I had issues with rex, dealership asked to run it once a month long enough that gas is recycled within 3 months. I have been practicing that for a year so far no issue except there is that feeling of guilt for polluting!

Just keep a minimum amount of fuel in the tank, less to go bad and less needed to add to it to keep it good, although having said that we have had the REX for 3.5 years and the only running it gets it the maintenance cycle and maybe once on a very occasional long run each year, we keep the tank usually fully topped and had no issues at all, maybe try a better fuel?

I was not lucky as you. I think hot and humid weather might have made a difference. Not really sure though.

 

[symonray]

My recent experience with my new (to me) 2017 CPO i3 Rex has convinced me to continue regular use of the Rex (with the hold state of charge function) like I did with my 2016 Rex. The vehicle history information I received for my 2017 was that the prior owner almost never used the Rex and may have left only a small amount of gasoline in the tank for long periods of time (which may have prevented the Rex regular maintenance cycle from engaging). Less than two weeks after I took delivery of the vehicle and after a couple of extended uses of the Rex, the CEL illuminated, and the dealer diagnosed it to be caused by fouled fuel injectors and a bad O2 sensor. The repairs were covered under warranty, and the Rex is now running fine.

 

[Geodude]

PanamaMike Wrote:

To keep Rex in good working order. I know there is a Rex maintenance cycle that will run, but is that enough?

Hey PanamaMike, I like to run the REX on my 2017 at least once a week for 10-20 mins. The good thing about coding your i3 is that you can use "Hold State of Charge" anytime after your battery charge is 75% or less. Then you can turn it on whenever you'd like. Keep in mind when you go to uncheck the "Hold State of Charge" box, it does take about :60 seconds for the REX to turn off and go back the the battery use side. Absolutely love having the REX on the i3. Takes your mind off of any "Range Anxiety" you may have. One of my friends owns a Tesla, and he is always thinking about how much "Charge" he has left. Even a Tesla with a 300 mile range people worry about how much charge they have. BMW's i3 with the REX, you never have to worry my friend.

 

[Deutsch100]

PanamaMike Wrote:

To keep Rex in good working order. I know there is a Rex maintenance cycle that will run, but is that enough?

Hey PanamaMike, I like to run the REX on my 2017 at least once a week for 10-20 mins. The good thing about coding your i3 is that you can use "Hold State of Charge" anytime after your battery charge is 75% or less. Then you can turn it on whenever you'd like. Keep in mind when you go to uncheck the "Hold State of Charge" box, it does take about :60 seconds for the REX to turn off and go back the the battery use side. Absolutely love having the REX on the i3. Takes your mind off of any "Range Anxiety" you may have. One of my friends owns a Tesla, and he is always thinking about how much "Charge" he has left. Even a Tesla with a 300 mile range people worry about how much charge they have. BMW's i3 with the REX, you never have to worry my friend.

Exactly how I feel about my i3S Rex Geodude! I have no range anxiety!

 

[Pahaska]

I have a friend with a top of the line Tesla. She can not easily visit her daughter since there are no charging stations in rural Texas and it takes forever to recharge with the 120v charger. She has to stay overnight to make the trip work for her.

Much happier with my REx. There are plenty of gas stations everywhere I need to go. My longest trip so far was San Antonio to Austin and I arrived home with 70% battery left. I coded it in a parking lot 2 blocks from the dealer. I ran the REx the whole way since I had only the 120v charger at home. I now have a Clipper Creek Level-2 and I don't worry so much about getting the battery far down since a couple of hours brings it back up.

 

[spartacus68]

A lot depends on climate, but engines need to be run regardless.

I have a separate thread on issues with my wife's car and a drive-train error that was eventually linked back to the fuel pump relay, but not before the technicians at BMW replaced the oxygen sensor and fuel pump at considerable expense.

Going forward, once a week or at least every other week seems to make sense for a good 30 mins or so, certainly in Northern Europe where conditions will remain wet or cold until the spring. It's an expensive fix otherwise.

I think the key thing here is, unlike BEV i3 owners who are always aware of the range of their vehicle, REx owners can be lulled into thinking all is well, and for a dash error to remind you otherwise!

 

[jadnashuanh]

The engine is fairly small, and the exhaust isn't all that long like it is on many where it needs to travel the full length of the vehicle to exit from the rear, so it should come up to temperature fairly quickly. What's not great for any ICE is lots of short, cold starts where it does not get warm enough to get rid of the water generated during the combustion process...you want not only the engine, but the exhaust to get hot enough so any moisture will exit via a gas rather than condense and sit inside. That's true in the engine as well, and particularly the oil (which is one of the first things to get hot).

Also note that in some places, you just can't buy fuel without ethanol in it. If you do not use the fuel after awhile, the ethanol can phase change from the fuel, and worst case, if things aren't sealed well, the ethanol absorbs moisture and eventually gets saturated. That shouldn't happen in a sealed fuel system, but no guarantees! When you use fuel, it still has to let air in and that WILL have some moisture in it. It's not supposed to let air/fumes out, though. With that in mind, it's better to have the tank full, as that means there's less air to expand and contract, thus, less being pulled in, so less chance of moisture being introduced.