Bgw70

maarp

Cheers all. Not wanting to burn bridges, just get my panties wadded at times.

DshngDaryl

I would agree with that. I used to have a Volvo C70 convertible and a 25 mile commute. I figured that burning 87 octane for twenty miles on Cruise Control wouldn't hurt anything.

It didn't, but I noticed I got 2 miles less per gallon and the car wasn't as quick off the line.

Back then 91 was only 10 cents more a gallon.

I did the math in my head. If I was getting 26 miles a gallon for $3.00 or 24 miles for 2.90 it was cheaper, per mile, for me to run Premium.

Full disclosure, that was like 15 years ago, so I don't remember the actual miles and gas prices. But I do remember the math worked out.

Bgw70

maarp

The pump price goes down? Lol

Also, all the gas stations raise the price the same amount at the same time, but there's no collusion. That would be wrong.

Bgw70

Jabberwock

In most cases with a modern computer and sensor controlled high compression car engine, running regular in it will produce lower mpg due to engine not running at "ideal" settings (various alternative run time parameters used if the ECU detects any kind of pre-ignition from lower octane being run ). In some cases the mpg degradation will equal or exceed the cost differential between regular and premium so there is no cost savings in running lower octane.

To be clear the only difference between higher octane gas and regular octane is the higher octane gas has a higher pressure combustion point. The greater the compression, the higher the temperature within the combustion chamber. And the higher the temperature, the greater the thermal efficiency and power produced. There are no other differences. Premium does not have more energy, it is not cleaner, it does not burn better...there are no other differences besides a higher pressure/temp combustion for premium despite the years of marketing hype and BS most adults have been exposed to by gas retailers.

My individual experience having tested regular versus premium tanks of fuel over the course of multiple road trips (1-1.5 k trips) is that on the LS430 there is no change in mpg.. I assume there would be less power at some rpm range using regular if the ECU has set the timing slightly back to accommodate using regular, but I personally did not feel it (but I would be unlikely to feel a power loss as I drive like an old geezer 95% of the time). I assume the SC430 engine which is identical in most ways, would produce same or similar results. Most of my trips were on a very flat interstate cruising at pretty constant 70-75 mph with the engine is loafing along. Given the ECU is constantly monitoring engine sensors (MAF, temps, O2, etc.) and is making changes based on those readings, there actually may not be a change in mpg or power under easy driving conditions that do not stress the motor.

Running the same test on a more difficult roads, and/or at higher speeds, or higher ambient temps, or more aggressive driving style might produce much different results.

jimaleg

What if you 50-50 mix 87 octane regular with 93 premium will that produce an octane of 90?

jimaleg

What if you 50-50 mix 87 octane regular with 93 premium will that produce an octane of 90?

Lavrishevo

iTrader: (1)

There is also evidence that prolonged use of regular or 87 can lead to premature failure of the catalytic converter system. This is due a less than ideal combustion within the engine and fuel gets into the cats. The car will run on low octane but it is not designed / programed to use this fuel. By using 87 you are forcing the car to pull timing to avoid knocking. Best to use 91 and above and use a fuel system cleaner often. Marvel Mystey Oil (MMO) works great and is much cheaped than other products. One bottle will treat 4 - 5 tanks of fuel for $4. Also fantastic to help clean the carbon out of the engine. Add about 1/2 a bottle with your oil change. I use religiously in all my vehicles. Not some miracle product. Just does what it's supposed to. Cleans carbon and uses friction modifiers to help protect against cold start wear.
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iolmaster

iTrader: (1)

Please provide the sources of your evidence.

Lavrishevo

iTrader: (1)

I will give you a very easy example you can try yourself. If running 87 for a few tanks and you open her up, WOT, you will smell more of a rotten egg smell vs premium fuel. This is true to many cars that prefer premium fuel. That smell is fuel entering the exhaust system without being burned. This will eventually ruin catalytic converters.

iolmaster

iTrader: (1)

Absolutely ridiculous. Please provide the evidence you said you have. Not some anecdotal evidence that has no basis in science. I don't know where you would get this stuff.

TitanG545

Funny I just gave my 430 her first fill up Friday since owning her. I got her back from the detailer and stopped at BJ's and put in premium, I don't recall the number. Then put a few bucks in my 400 today on my way into work. I was running late but put 91 in, will fill up with 91 on my way home.

Lavrishevo

iTrader: (1)

I have had multiple Lexus master techs speak to me about this be a potential cause. I had cats fail on a my LS400 prematurely and the previous owner ran 87 its whole life. Anyway, it's a theory and I can't personally prove it. But it does make sense that less than ideal combustion leads to more fuel not getting burned and hence degradation of the catalytic converter system. If you think it is ridiculous than more power to you. Keep running 87. If you don't understand how pulling timing works to prevent knocking and how this creates a less than ideal combustion within the cylinder than read up about it.