Does 2023 RX require premium gas?

exodusNH wrote: ↑Tue Jul 12, 2022 11:33 am

Leesbro63 wrote: ↑Tue Jul 12, 2022 10:22 am Many Bogleheads are Lexus owners and many of those drive the RX midsided SUV. I have a 2020 and am considering ordering a 2023. My dealbreaker is that it seems that the 2023 will come with a 4cyl turbocharged engine that requires premium gas. I absolutely hate buying premium gas. Some on the Lexus board say to ignore the requirement, but I don't feel good about buying a $60,000 vehicle and putting in sub-optimal fuel. It appears that premium is about 15% more costly at this time. Will this vehicle get more than 15% better MPGs? I doubt it. Anyone have thoughts about this?

1. If you don't use premium, the computer will compensate by altering the engine's timings. The result will be worse gas mileage.

2. "Premium" fuel has same energy as 87. It simply can handle more pressure before detonating. High performance engines run at higher compression and need the higher octane fuel. It's not "premium" in any way -- the name was chosen by the marketing folks.

3. The turbo crams more air into the engine. That requires more fuel than a naturally aspirated one. Unless you drive like a grandmother, you will get worse mileage in a turbo than a non-turbo.

4. The turbo is also harder on the engine and will result in shorter engine life. Maintenance costs will be higher.

1. I agree that's possible. Other posts pointed out correctly there's no appreciable difference in BTU/gallon among grades of fuel, but if the engine, especially turbocharged, is optimized to run on 93 it will probably get lower mileage as well as delivering less power if you use 87, as the engine adjusts itself away from its design point to avoid knock thus avoiding actual damage or maintenance issues, within limits. Bad idea IMO to use fuel below the *minimum* specified in the manual.

For turbocharged engines that effect might be greater. Also OP's original question wasn't whether premium would get bet better mpg in the 4 cyl turbo RX than regular, but whether the 4 cyl turbo would get better mpg on premium than the older 6 cyl naturally aspirated (NA) would on regular. Probably, probably the main reason Lexus made the engine change, to meet a fleet mpg requirement under US CAFE requirements, since most Lexus sales are in the US. But the CAFE mpg rating is unrealistic (comes out substantially higher than EPA rating some drivers don't think fit their results) and I don't guess Lexus insisted the design change actually cut fuel costs considering the cost of premium. They probably just aimed to sell the desired number and types of cars under the CAFE standard without increasing fuel cost *too much*, and also probably made the decision before the recent spike in gas prices.

2. Right so putting higher octane fuel in engines tuned for lower octane doesn't accomplish anything, at best. But putting lower octane fuel in engines tuned for high can reduce both power and mpg, even though the modern engine adjusts itself to prevent damage down to some limit (manual for my Porsche says it can use *86* in an 'emergency', but 'do *not* floor the accelerator' and 'this may reduce performance and increase fuel consumption'; recommended is 'at least 91' and for other Porsche models it's 'at least 93', IOW drivers of those cars in the western US are using below recommended octane fuel all the time if they go to regular gas stations where 91 is max).

3. Don't agree here. Two other things are happening with the turbocharger a) it's recovering some of the otherwise wasted energy in the exhaust gas when the engine is running at least fairly high % of max output b) the engine can be smaller and have the same max ouput, 4 cyl 2.4l in this case v 3.5l v6 previously so frictional losses are less when the engine is running at low power even though turbocharger is just 'windmilling' in that common case, for cars. The trend toward smaller turbocharged engines replacing larger NA ones in various models of not particularly performance oriented cars in recent years is mainly to improve mpg.

4. Again I don't agree here or at least it's more complicated than that. What you say was definitely true back when say I bought a turbo kit for my Volkwagen bug's aluminum flat 4, cool power increase but also just increased max pressure, heat stress etc over what the engine was originally designed for, even with additional oil cooler (didn't actually blow up though

). In between then and now various car manufacturers struggled with engine reliability of turbocharged engines designed to be, but no inherent reason you can't achieve the same reliability as NA engine and I doubt you'll see statistically significant difference in engine problems in a Lexus NA or turbocharged you buy now. In some categories of ICE, like large low speed diesels on ships (I used to climb into the cylinders of) there's been no such thing as non-turbocharged for decades.

Does the 2023 rx350 use regular gas?

What happens if you use regular gas instead of premium in a Lexus?