Premium gas for 2016 RX 450h?
Intermediate
Joined: Sep 2016
Posts: 363
Likes: 104
From: WA
I have never once heard a knock or ping out of my engine - even when pulling our little motorcycle trailer. I remember the V-8s of the early 1980s. They would knock & ping continuously on the highway & were absolutely gutless wonders. I feel pretty confident that the Toyota engineers have figured out how to keep this hybrid engine from self destruction.
Instructor
Joined: Oct 2016
Posts: 857
Likes: 47
From: Oregon
So what the manual is saying is that if you can't find premium, then regular is fine. And if you hear knocking, go back to premium.
So one question is whether anyone has ever heard knocking with these engines. Since they use an antiknock sensor, my guess is "no," but I could be wrong.
So one question is whether anyone has ever heard knocking with these engines. Since they use an antiknock sensor, my guess is "no," but I could be wrong.
Lexus Champion
Joined: Sep 2016
Posts: 2,047
Likes: 135
From: AB
Shadowmite above had mentioned that I had made a comment on compression ratios in another thread. For what it's worth, here's what I wrote over there in response to a commenter's statement that premium fuel was needed due to a very high compression ratio:
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There's a bit more to the story these days, which is why your reasonable compression ratio rules-of-thumb probably don't apply.
Toyota hybrids use an Atkinson-style engine design, not the traditional Otto-cycle. They do so in order to gain an additional 5% or so improvement in efficiency. Efficiency comes from having a very high EXPANSION ratio, such that the engine gets as much energy out of the expanding charge as possible before opening the exhaust valve. In a traditional Otto engine that meant having a high COMPRESSION ratio also (both were locked together), which meant too-high cylinder BMEP and engine knock. But in the Atkinson, Toyota leaves the intake valve open for part of the upstroke, so the total charge at the time of ignition is reduced. This means less power but, again, more efficiency. My 2010 RX450h engine has 240HP versus about 270 for its Otto-cycle cousin, but in the hybrid we also have electric motors to assist, so in fact the hybrid car has more total HP than the cousin. Very clever.
So don't look at the expansion ratio to see if premium fuel is needed. It's not. The engine is a whole different animal. And, as already mentioned, every modern engine uses a knock sensor that will kick in if necessary.
Car manufacturers use the "premium fuel" tag to maximize the specs and EPA ratings. As long as you use high-quality regular fuel, the engine will be perfectly happy but you'll lose a few HP and a fraction of an mpg.
-----------------------------
There's a bit more to the story these days, which is why your reasonable compression ratio rules-of-thumb probably don't apply.
Toyota hybrids use an Atkinson-style engine design, not the traditional Otto-cycle. They do so in order to gain an additional 5% or so improvement in efficiency. Efficiency comes from having a very high EXPANSION ratio, such that the engine gets as much energy out of the expanding charge as possible before opening the exhaust valve. In a traditional Otto engine that meant having a high COMPRESSION ratio also (both were locked together), which meant too-high cylinder BMEP and engine knock. But in the Atkinson, Toyota leaves the intake valve open for part of the upstroke, so the total charge at the time of ignition is reduced. This means less power but, again, more efficiency. My 2010 RX450h engine has 240HP versus about 270 for its Otto-cycle cousin, but in the hybrid we also have electric motors to assist, so in fact the hybrid car has more total HP than the cousin. Very clever.
So don't look at the expansion ratio to see if premium fuel is needed. It's not. The engine is a whole different animal. And, as already mentioned, every modern engine uses a knock sensor that will kick in if necessary.
Car manufacturers use the "premium fuel" tag to maximize the specs and EPA ratings. As long as you use high-quality regular fuel, the engine will be perfectly happy but you'll lose a few HP and a fraction of an mpg.
When I had '15 450h, owner's manual suggested premium gas. When I had Acuran MDX manual said same and even warned possible engine damage which may not be covered by warranty.
Benz bi turbo V8 manual says minimum Octane 91 or higher. Also improper gasoline caused damage will not be covered by warranty. ECU keeps the history of engine operation.
Also the terrain where the vehicle is operated has something to do it too. ECU just can't retard timing indefinitely. Simply put follow the manual to keep the car running within design specs.
Save few $$ filling up, lose some Hp and acceleration time and possible engine damage... why bother? All vehicles in my family run on Shell premium always.
Last edited by Htony; Feb 25, 2019 at 04:28 PM.
Intermediate
Joined: Sep 2016
Posts: 363
Likes: 104
From: WA
^ You bring up a point I had not thought of - if the ECUs record knocking issues and that leads to trouble, I'm wondering then if the car's own data will work against the owner. Out of warranty it would not matter - owners problem. But in warranty or extended warranty it might.
Lexus Champion
Joined: Sep 2016
Posts: 2,047
Likes: 135
From: AB
I have never once heard a knock or ping out of my engine - even when pulling our little motorcycle trailer. I remember the V-8s of the early 1980s. They would knock & ping continuously on the highway & were absolutely gutless wonders. I feel pretty confident that the Toyota engineers have figured out how to keep this hybrid engine from self destruction.
specially when owner's manual recommend premium gas. Additional benefit of premium gas is that i contains more detergent to keep your engine clean minimizing carbon
foul up specially on DI type engines. I never drive on regular gas. Saving few bucks is more important than pleasant driving? Purring engine, swift acceleration, peace of mind. In europe they even has Octane 97 gas. Even in Korea they have Octane 94 at the pump. My car psecifies minimu Octane 91.
Racer
Joined: Oct 2016
Posts: 1,404
Likes: 215
From: Texas
Today's engines are more fine tuned, electronic controlled. Knock sensor is a Piezo transducer designed to specific. frequency to detect knocking. B4 you hear it ECU always retarded timing to prevent knocking. High altutude, pulling heavy load, etc. will increase the chance of knocking and using regular fuel vs, higher Octane premium
specially when owner's manual recommend premium gas. Additional benefit of premium gas is that i contains more detergent to keep your engine clean minimizing carbon
foul up specially on DI type engines. I never drive on regular gas. Saving few bucks is more important than pleasant driving? Purring engine, swift acceleration, peace of mind. In europe they even has Octane 97 gas. Even in Korea they have Octane 94 at the pump. My car psecifies minimu Octane 91.
specially when owner's manual recommend premium gas. Additional benefit of premium gas is that i contains more detergent to keep your engine clean minimizing carbon
foul up specially on DI type engines. I never drive on regular gas. Saving few bucks is more important than pleasant driving? Purring engine, swift acceleration, peace of mind. In europe they even has Octane 97 gas. Even in Korea they have Octane 94 at the pump. My car psecifies minimu Octane 91.
I bought Chevron fuel over the weekend. 87 was $2.20/gal & 91 was $2.60/gal. That was a $6.00 difference, just on this tank. If I bought fuel every week, that would be at least $312 difference per year or $1248.00 difference in 4 years of ownership. These are just some minimums. I don’t see the justification here, but I do see the personal preference. Someone mentioned Bentley would void a warranty for too low an octane. So what? We aren’t discussing Bentleys. That would be extremely hard to prove anyway. If the vehicle had a tank of 91 when it entered the shop, what are they going to use as proof? How do you know your ECU isn’t picking up knocking with 91 octane & recording it in the history? What if it does?
The key to longevity of any vehicle is regular maintenance. If that doesn’t occur at least somewhat close to manufacturing recommendations, the owner is at fault.
Lexus Champion
Joined: Sep 2016
Posts: 2,047
Likes: 135
From: AB
No disrespect towards you, as you are free to have whater opinion you want. However, there have been several studies done comparing 87 vs. 91 octane unleaded fuels. Does an engine run better on 91? More than likely. Will an engine be destroyed by 87? Absolutely not. When is the last time you heard about an engine of any kind being destroyed by using lower octane fuels? It just doesn’t happen. Car Talk debunks many of these myths & back up their opinions from the American Petroleum Institute: https://www.cartalk.com/content/prem...egular-0#myth4
I bought Chevron fuel over the weekend. 87 was $2.20/gal & 91 was $2.60/gal. That was a $6.00 difference, just on this tank. If I bought fuel every week, that would be at least $312 difference per year or $1248.00 difference in 4 years of ownership. These are just some minimums. I don’t see the justification here, but I do see the personal preference. Someone mentioned Bentley would void a warranty for too low an octane. So what? We aren’t discussing Bentleys. That would be extremely hard to prove anyway. If the vehicle had a tank of 91 when it entered the shop, what are they going to use as proof? How do you know your ECU isn’t picking up knocking with 91 octane & recording it in the history? What if it does?
The key to longevity of any vehicle is regular maintenance. If that doesn’t occur at least somewhat close to manufacturing recommendations, the owner is at fault.
ECU is like a black box on an airplanes. They store operating paramnters in it's memory. That is my understanding.
Rookie
Joined: May 2019
Posts: 63
Likes: 11
From: California
Been using regular. I did a short test from sf bay area to lake tahoe. Premium there, regular on the way back. They both felt the same and both got the same mpg of 29-30 mpg. Ever since then i been using regular. Zero issues so far
Racer
Joined: Sep 2012
Posts: 1,304
Likes: 177
From: WA
You probably psychologically felt better using regular and it changed your driving habits as follows: drive with a heavier foot (due to cheaper gas) and then coast on electric power longer because you got up to speed faster. This is how you're supposed to drive a hybrid and will improve your fuel economy. It's not about the length of time you use electric power, it's about how long you can keep your gas engine turned off.
The energy stored between regular and premium is the same.
The energy stored between regular and premium is the same.
Advanced
Joined: Apr 2017
Posts: 701
Likes: 166
From: NSW
You probably psychologically felt better using regular and it changed your driving habits as follows: drive with a heavier foot (due to cheaper gas) and then coast on electric power longer because you got up to speed faster. This is how you're supposed to drive a hybrid and will improve your fuel economy. It's not about the length of time you use electric power, it's about how long you can keep your gas engine turned off.
The energy stored between regular and premium is the same.
The energy stored between regular and premium is the same.
I do a regular drive (every six weeks) up and down a freeway, 750 kms each way and a few extra trips too.
I've tried each of the three fuels we have, 91, 95 and 98 (in Australia), at different times and virtually full tanks of the same fuel. Every time I've had a better consumption figure with 95 compared to 91 and 98 is better again. The price difference though means the fuel savings are offset by the extra fuel cost so I've just stuck with 95 (Lexus recommended).
Driver
Joined: Aug 2013
Posts: 155
Likes: 14
From: CO
Actually the energy density between regular and premium is not the same. Regular packs a higher density due to not having additives designed to make it less explosive. https://www.appropedia.org/Energy_content_of_fuels
That said, I also agree it's likely caused by a change in driving habits as the actual energy density would be greater affected by the summer/winter 5% ethanol addition than by the energy difference.
That said, I also agree it's likely caused by a change in driving habits as the actual energy density would be greater affected by the summer/winter 5% ethanol addition than by the energy difference.
Rookie
Joined: May 2019
Posts: 63
Likes: 11
From: California
I did numerous tests . Going on a road trip and heavy city driving . Heavy foot, light foot , cruise etc.. the regular performed better. It's personal preference for me and i will continue using regular as there is no difference in performance . i know people like to grill regular gas users here but please don't hesitate especially if gas prices are high. Regular is fine. But when gas is cheap sometimes il use the premium , still don't notice a change in performance. Someone will say well in the long run your car will suffer , well let's see about that. It's a lexus it's supposed to be reliable right. My buddy who works at lexus checked out the car and he said everything was fine and recommended whatever gas you feel like. If it gives you peace of mind to get premium im for it. Don't hesitate using regular either because it's SOS