So at 300k miles and 15mpg we are talking 20,000 gallons, which at .50 per gallon difference, equals $10k is gas differences. A rebuilt 3UR-FE is 5k plus labor is $1k, so for $10k i can pay for almost 2 rebuilt engines and labor.
I don't argue that it has a negative effect on the engine and that in turn will affect engine life, i just don't picture it affecting it to a point where it would require engine replacements often enough (every 180k miles @ 15mpg = 12k gallons = $6k) to justify the higher cost in gas. I feel that this is especially true for me since i did not start it on RUG until about 182k, or 1500 miles ago.
Do you have reasons to believe that running regular vs premium may cause a freshly rebuilt engine to die before reaching 180k? If not then i think i will take my chances, especially considering that the engine already has 182k, so even if the impact over the next 100k is as significant as you imply, then it still wouldn't be a bad run for this engine even if it dies out around then. Again, i have a tough time picturing that the impact would be that significant, but i am no expert on this matter.
If i were to be honest, i run it because my dad suggested it, and that is good enough for me. If it turns out that we are both wrong, then i am okay with admitting and accepting responsibility for it, and from there go with the recommended premium for the next engine.
What i won't do, is allow my mistake to become the next owner's problem, nor do i plan on there being a next owner for this car unless it is to a friend/family. I do see where you are coming from though and i appreciate you trying to educate me on the matter/make sure i don't make a costly mistake.
Looking at this from a financial perspective might be useful for the pocketbook, but like many things, why do we indulge in an 200-series when a used Nissan might do. Or invest in a roof rack, when the stock one will do. To this topic, using premium is not all poured down the drain. The case for premium can have more to do with efficiency often, than power. Which is why there's been a movement in the auto-industry in the last decade towards premium, even in lesser cars, as they chase MPG numbers. The LX likely requires premium to compensate for its added weight over the LC.
Higher octane fuels may actually have less energy content than lower octane. Octane is a measure of resistance to uncontrolled combustion. Where it pans out is by allowing more timing advance (dynamic compression), to better extract what energy content there is in fuel. This is governed by the software calibration independent of hardware.
Do I believe running regular may kill an engine before reaching 180k?
How are you using your vehicle? Plodding along, it probably won't care, which is why so many believe it's okay.
Tow a heavy load, on a hot day, climbing a grade, using a bad batch of 87 octane, with a worn engine, and it may not. Knock sensors are a mitigation to these variables. Mitigation does not make for a good control strategy. One can choose to use the mitigation everyday to get by with 87 octane by riding the knock sensor, slowly adding microscopic deposits, etching, and fatiguing the combustion chamber. Then that mitigation strategy may just very well come up short one day.
I apologize to everyone if they are offended by the word layman. The negative connotation was not the intent. It was only to say that people are making strong recommendations to others without specialized knowledge on this topic. Just as everyone of us has our areas of expertise, I wouldn't try to step into someone else's domain and tell them how to put out a fire for example. That would make me a layman on that topic.
From the horses mouth:
Per Lexus LX 570 instruction manual, p 684.
"Premium unleaded gasoline only"
"91 (Research Octane Number 96) or higher"
p 692:
"If 91 Octane cannot be obtained, you may use unleaded gasoline with an Octane Rating as low as 87 (research octane number 91). However, use of unleaded fuel with an octane rating lower than 91 may result in engine knocking or drastically reduce output to protect itself while driving a heavy load. Persistent knocking can lead to engine damage and should be corrected by refueling with higher octane unleaded gasoline."
p 692:
"Premium unleaded gasoline with an octane rating 91 or higher required for optimum performance."
If there were a money saving strategy that I would adopt for the LX, is to perhaps use 89 everyday. 91 only for heavy use. 2 points of octane is probably within the margin of safety. 4 points is a pretty big stretch. Timing numbers from the ignition maps I have tuned in various vehicles vary dramatically between 87 to 91, which would definitely cause an engine to ride the knock sensor on load.
, I would hope that the modern ecu are programmed to be adaptive to different formulations. When I used lower octane gas in my other Lexus, the difference was felt mainly in acceleration but there was no knocking. However, this could be placebo effect too.
