I searched around and couldn’t find an answer.
The fuel fill opening on my new IS350 looks and functions differently from my old 2017 IS300.
There is a white plastic insert/sleeve. The gas pump nozzle won’t enter as far into the opening. The gas pump nozzle has a circular rubber seal, which does not sit tight to the fuel fill opening. What is that plastic insert? Seems like it could break at some point sending plastic pieces into the gas tank.

 

I noticed that on my '22 yesterday. The pump won't stay locked, I had to keep holding the lever in. Didn't really think it was an insert just a different fill nozzle.

 

Here is a pic showing the white plastic insert. Did not have that in my old IS.

 

This is actually very interesting because everytime go with my 2022 IS350 to the gas station, person filling up my car (yes I’m from only state that we cannot tank ourselves… New Jersey) has to stand by my car otherwise after few seconds it will get interrupted (tested on Shell, Sunoco, Wawa etc.).
I almost always have to tell them when my car is full of gas otherwise they have no idea.

It doesn’t happen with my wife’s 2021 NX300 🤔

 

From what I've read they REALLY don't want us to top off our tanks so maybe that's why the mouth is designed like this

 

Just watched a YouTube video from a Toyota mechanic that gave top 5 things NOT to do with your Toyota. In that list was to not drive the car close to empty on a regular basis. Some people get low then put $10, $20 worth of gas and it doesn't fill up. The fuel pump and sending unit works by being submerged in the gas tank and cooled by the gas. Running it low all the time burns them out and causes them to require replacement sooner than necessary. And he said that's a very expensive repair. That could be why the engineers 1)don't count the final 2 gals of fuel in the estimated to empty mileage # and 2)maybe why they don't want us to top off the tank. He said the tank requires ventilation and topping it off fills those air tubes that also cause damage.
I'm not a mechanic by vocation, so I'm just relaying what a mechanic said.

 

Strange, I've never had this issue on any of the three 3rd-gen ISes I've owned. But, I can say I've seen posts about this before.

 

Getting back to my concern/observation with my new 2023 IS350. Take a look at the pic I posted.
Do your 2021-2023/4 versions have that white plastic insert? I was just concerned that it might
be a left over piece that should have been removed
after assembly/transport.

I had problems with premature shut off with my 2017 IS, but that occurred only at certain gas pumps.

 

2023 IS 500 here, and I've had the white plastic piece there as long as I have had the car. It hasn't given me any problems.



It's wet in there because I washed the car earlier today and didn't dry inside the fuel door.

 

To keep people from accidentally trying to fill up with diesel?

 

I think that a diesel hose nozzle is already too large a diameter to fit a gasoline fuel tank opening for that very reason. But I think that you are on right track, that it is a restrictor of some sort. It seems to be restricting the gasoline nozzle a bit for me. The nozzle is not going in as far as on my old IS tank without the restrictor.

 

Upon further review, leaded and unleaded nozzles also differ in size. The insert/restrictor may be for that purpose?