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2014 Lexus RX 450h - What if I skip Premium?

How likely is engine knocking and resulting damage to occur if I do not use premium gas?

If this vehicle says use Premium fuel ( Required ) in your manual do you really want to take a chance on having to buy a new engine for several thousand dollars . If this is a problem then trade for a different vehicle.


And yet another post from someone with an expensive luxury vehicle yet is reluctant to spend the extra money to use the fuel specified by the manufacturer. SMH.


Very likely

I will go against the grain and say that is unlikely that you will suffer engine damage. You will experience less mpg and power, but I am quite confident that your vehicle will make the adjustments needed to the timing to compensate. It appears that the non hybrid version doesn’t require premium, and it has basically the same engine, although probably tuned differently.

The engine has knock sensors.,2014,rx450h,3.5l+v6+electric/gas,3306989,exhaust+&+emission,knock+/+detonation+sensor,5108

But there will be a loss of performance from the engine.

The computer won’t allow the engine to knock.


So, this is hybrid and supposedly it sips fuel where non-hybrid would gulp it.
Now, engine performance will definitely suffer, for which hybrid system would most likely try to compensate, most likely increasing the fuel usage and decreasing performance.
Money is likely to be a wash, performance will suffer.
Longevity aside, what is to be gained here?


If the OP bought this hybrid vehicle with the goal of saving money on gasoline…
Why would she do something that is pretty-much guaranteed to decrease her gas mileage?


With 245 horsepower plus electric assist I doubt most people would notice any loss in performance.

You’re probably not going to save any money. When the knock sensor detects knock it retards the timing for less performance and gas mileage. You also run the risk of the knock sensor failing which can be catastrophic. I’ve torn into an engine that was destroyed by excessive knocking…It wasn’t worth rebuilding.


I agree. While I am not willing to pay the extra 50 cents a gallon for premium fuel, I also make sure to never buy anything which requires or even recommends it. I am really struggling to understand the logic of buying a high-performance car which requires premium fuel, and then asking if it’s ok to “cheap out” and use regular. It’s not like it’s that difficult to find a car which is designed to run well on regular (and cannot even benefit from using premium)!

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Here’s what your owners manual says, seems pretty clear:

Premium unleaded gasoline with an octane rating of 91 (Research Octane Number 96) or higher required for optimum engine performance. If 91 octane cannot be obtained, you may use unleaded gasoline with an octane rating as low as 87 (Research Octane Number 91). Use of unleaded gaso- line with an octane rating lower than 91 may result in engine knocking. Per- sistent knocking can lead to engine damage and should be corrected by refueling with higher octane unleaded gasoline.

“If 91 octane cannot be obtained, you may use unleaded gasoline with an octane rating as low as 87”

So 87 isn’t forbidden, according to the OM.
87 might be worth trying in the winter months.
Tendency for spark knock varies with intake air temperature.

??? Premium is “required”, and using regular could cause knocking and engine damage.

I become very angry with people whose cars require premium but use a lower octane fuel. I had a vehicle that required premium and when I would go out late at night and siphon fuel from cars that required premium but the owner substituted regular, then my car would ping. I think there should be a federal law against people who put lower octane fuel in cars that require premium. We gasoline thieves don’t want our engines damaged by tight wad owners of luxury cars.


Sub-optimum performance is what most drivers ask of their engines almost all of the time. Mashing the gas pedal to the floor and not shifting into a lower gear is a rare circumstance for most careful drivers. That is the one scenario I can think of where the optimum performance would be demanded by the driver, but not supplied by the engine.

Hill-climbing would also be… less than optimal… IMHO.

Consider that hybrids specifically alternate between the modes of “battery-only” and “supplying power to the wheels PLUS charging battery” specifically to reduce the percentage of time when engine works in unproductively low power mode.
You might assume that in hybrids, engines work harder, but lesser time-wise.
Connect the dots with reduced fuel quality…


I’m not worried about performance. I’m worried about the warning about engine damage.

If or when I buy a car that requires premium, I don’t think the extra cost for gas would be a problem, but so many are one paycheck away from disaster, If I was 1 paycheck away from disaster I would understand that we might like bologna instead of raman noodles. I am as tight as a thread stripped screw, and I really wonder sometimes how businesses and people are able to survive. I think there many out there with no idea of how great it is to find a $20 bill in a dirty pair of jeans.