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2022 Santa Cruz SEL Premium 2.5T AWD
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I have about 1500miles on mine now. I'm getting 24-25mpg in (Smart Mode). I found out with further research (Read the manual) That is mode isn't only for economy. It actually learns your driving habits and adjusts accordingly I was getting 18-19 the first couple of weeks driving heavy footed most often in sport mode. Then went to normal for a while and I was hitting 21-22 and now for the last 2 or 3 fill ups it has increased to 24-25.
I'm convinced that some of that increase is because it is getting broken in a bit. But I haven't changed my driving habits (still heavy footed) And my numbers are climbing. That's on mid-grade 89 octane.
 

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If you look at the manual minimum fuel is 87 (recommended 93) I'm at about 1300 miles and noticed a 1-2 mpg difference between 87 and 93, however the bigger question is it says the fuel capacity is 17.7 gallons, and running it almost to empty I've never been able to get it past 13.56 gallons when refueling. Anyone else noticed it as well?
 

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Discussion Starter · #7 ·
YES!

I ran down DTE to 9 miles.

Only able to put in 14.4 gallons.

91 octane fuel at Costco.

87 is lower mpg??
 

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YES!

I ran down DTE to 9 miles.

Only able to put in 14.4 gallons.

91 octane fuel at Costco.

87 is lower mpg??
I ran mine down to 25 with 87 and then filled it to 13.5 gallons or so with 93 and after the rest of the 87 went through I saw an immediate change from 22.3 mpg to 25.4 on 93, also I've only driven in SMART mode so I have no idea about having it in other modes, I did just fill up again today with 87 and I'll see again how much the mpg drops.
 

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If you look at the manual minimum fuel is 87 (recommended 93) I'm at about 1300 miles and noticed a 1-2 mpg difference between 87 and 93, however the bigger question is it says the fuel capacity is 17.7 gallons, and running it almost to empty I've never been able to get it past 13.56 gallons when refueling. Anyone else noticed it as well?
I've read the owners manual before, it recommends 87, not 93. Putting in anything higher is a waste of money IMO.
Gasoline engine Unleaded Fuel Only Your new vehicle is designed to perform optimally using unleaded fuel having an octane number ((R+M)/2) of 87 (Research Octane Number 91) or higher. (Do not use methanol blended fuels) Your new vehicle is designed to obtain maximum performance with UNLEADED FUEL, as well as minimize exhaust emissions and spark plug fouling.
Regarding a 4-gallon reserve, that seems awfully high. Regarding running it almost to empty, are you looking at the fuel gauge or the miles to empty estimate? The latter seems to be more reliable estimate on most vehicles, as it seems manufacturers build in huge safety margins for people like me. I was having a long interesting conversation with my passenger and on a four hour drive once and was oblivious to not only the fuel gauge but even the idiot light saying FUEL UP, and didn't notice until the really old S10 pickup started surging, and luckily I was able to make it to a gas station and finally experienced true empty, lol! These days it seems when the dummy light comes on you can easily do another 50 miles.
 

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I've read the owners manual before, it recommends 87, not 93. Putting in anything higher is a waste of money IMO.

Regarding a 4-gallon reserve, that seems awfully high. Regarding running it almost to empty, are you looking at the fuel gauge or the miles to empty estimate? The latter seems to be more reliable estimate on most vehicles, as it seems manufacturers build in huge safety margins for people like me. I was having a long interesting conversation with my passenger and on a four hour drive once and was oblivious to not only the fuel gauge but even the idiot light saying FUEL UP, and didn't notice until the really old S10 pickup started surging, and luckily I was able to make it to a gas station and finally experienced true empty, lol! These days it seems when the dummy light comes on you can easily do another 50 miles.
I just took a look back at the manual yeah your right my bad lol, but when regular 87 gas is $3.20 here and 93 at Costco was also $3.20 I went right ahead. But yeah a 4 gallons for reserve and expansion is insane, and I usually go off till empty, with newer vehicles as it tends to be quite accurate these days. Also Idk if the Santa Cruz is the same as some other vehicles I've driven with a yellow low fuel and a message and then when you get really low you get a red low fuel and another message.
 

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Santa Cruz - Searching...
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91 octane fuel at Costco. 87 is lower mpg??
No. Octane rating has no effect on MPG. Octane effects engine knock from pre-detonation. Unless an engine is high-compression, or has engine management electronics that won't compensate, higher octane fuel is an unnecessary waste of money. It does nothing for performance or economy.
 

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2022 Sage Grey SC Ultimate
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That will depend where you are, Clutch. As I've mentioned before, around me, the difference is the amount of ethanol in the mix. Some pumps label 87 as 10 or 15%, 91 as 5 to 10% and 93 as ethanol-free. Other stations run 5% ethanol in their 93. Pays to know your local stations that way. The amount of ethanol WILL affect your MPG, as it's less energy dense. That's why E85 needs to be a minimum of 30% less expensive to be worth filling up with - because you're going to lose about 30% of your fuel economy when running on it. (Ethanol.)

Also, as far as performance goes, that also depends. In northern winters, an ethanol blend in lower octane fuels can be desirable for its anti-icing properties. Basically a built-in gas line anti-freeze. That's why our stations in Canada switch to a "winter blend" around this time of year ... more ethanol, prices drop a few cents per litre, and fuel economy drops until spring.
 

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There is a well-entrenched folk wisdom advisory that says frequently running your fuel level way down will reduce cooling of the in-tank fuel pump, causing it to fail sooner. I don't know if this is true or just internet jive, but replacing a fuel pump is a job I never want to do again!
 
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There is a well-entrenched folk wisdom advisory that says frequently running your fuel level way down will reduce cooling of the in-tank fuel pump, causing it to fail sooner. I don't know if this is true or just internet jive, but replacing a fuel pump is a job I never want to do again!
Modern fuel pumps are usually long vertical canister style, and have a intake with a debris filter right at the bottom of the tank, and are cooled not by being submerged in the tank but rather by the fuel flowing through the pump itself. So basically as long as its not sucking in air, its getting cooled just fine and when it runs out of fuel the engine stops in short order along with the fuel pump accordingly, so its self-protecting itself from damage either way.
 

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If saving money is your goal, the extra cost of Premium gas usually negates any small gain in gas mileage.
 

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I heard my name. :)

Octane and fuel economy

As @Clutch Cargo suggested, the octane number refers to the fuel's ability to resist knock/detonation/ping. It doesn't burn any "hotter" or "cooler" or "faster" or "slower" - it's simply more resistant to spontaneous combustion at higher cylinder pressures. There's no significant difference in the energy content between 85 and 93 octane. Also as stated, unless an engine is designed to take advantage of premium fuel, there's no value in using it. It used to be that premium fuel contained additional detergents, but a minimum amount of detergent is now required in all grades of gasoline. Top Tier gasoline claims to have additional detergents and is recommended by many automakers - including Hyundai. Most major brands are Top Tier. There's more to lose by running regular in an application that requires or recommends premium than there is to gain by running premium in an application optimized for regular. Unless the engine is designed to take advantage of premium, you're unlikely to gain any power or fuel economy and are just wasting money. The 2006-2014 Honda Ridgeline was a rare bird in that it was optimized for regular fuel, but would benefit from a slight power and fuel economy increase when using premium, but only when towing heavy loads. In this case, the owner's manual specifically stated that premium was recommended while towing.

Fuel pump

In-tank fuel pumps that appeared along with electronic fuel injection in the 1980s have always been cooled by fuel flowing through them - not around them. So, as @JASmith stated, as long as there's enough fuel flowing through the pump to keep the engine running, there's fuel to remove heat from the motor windings (the motor in a fuel pump is surrounded by fuel). Early fuel injection systems were "return type" where a fixed and relatively large volume of fuel moved from the tank to the engine and whatever the engine didn't use was returned to the tank. This allowed for some of the heat generated by the fuel pump to be dissipated by the fuel lines. Newer systems are "returnless" and have only a supply line to the engine - only the amount of fuel needed by the engine is moved out of the fuel tank while the rest flows out of the pump and back into the tank. Most fuel pumps operate at a fixed speed, but a few are two-speed or variable-speed. Most fuel tanks are now plastic which is a better insulator than steel.

The concern with running a modern vehicle low on fuel is that with no return line or steel tank to dissipate heat, more of the heat generated by the fuel pump itself that is transferred the fuel stays there resulting in higher fuel temperatures which in turn results in higher fuel pump temperatures in a repeating cycle. The longer you drive and the lower the fuel level and the hotter the ambient temperature, the harder it is on the fuel pump.
 

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The concern with running a modern vehicle low on fuel is that with no return line or steel tank to dissipate heat, more of the heat generated by the fuel pump itself that is transferred the fuel stays there resulting in higher fuel temperatures which in turn results in higher fuel pump temperatures in a repeating cycle. The longer you drive and the lower the fuel level and the hotter the ambient temperature, the harder it is on the fuel pump.
Other way around, it was tanks that had a fuel return line that were a concern with low fuel levels. In a return system, the pump adds a negligible level of heat to the fuel, but it would pick up a lot of heat flowing through the potentially very hot engine bay, and would return to the fuel tank, rinse and repeat. The more volume of fuel the less the average temperature rises. In a returnless system, the standing fuel really has no contact with the pump itself that is encased in an insulating plastic shroud, and there are no repeat heat cycles for the fuel to make as its a one-way trip and the pump has less work to do since less fuel needs to be moved, so its a more efficient cooler running design with less evaporative emissions accordingly and is pretty much the norm for OEMs now. Source: Fuel Pressure Explained - Injector Dynamics
A downfall of return systems is the fact that they circulate fuel through a very hot engine bay, ultimately carrying that heat back into your fuel tank.
Here's an example of a fuel pump module, where you can see the intake is at the bottom of the tank and protected from debris and its encased in plastic:
White Light Liquid Fluid Material property

tl;dr: You can run the fuel level down, won't hurt anything.
 

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The amount of ethanol WILL affect your MPG, as it's less energy dense.
Agreed. However, Octane Rating alone does not. Your insight on Canada having (allowing?) different levels of Ethanol for different levels of Octane is interesting to know. Sounds inconsist and convoluted! As you said "Pays to know your local stations that way." My response was to a post from someone showing registered in the USA, so presumably does not have those added complications. From the perspective of responding to the original question "91 octane fuel at Costco. 87 is lower mpg??", the answer is still NO (in the USA :)).
 

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SEL Premium Hampton Grey
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Lower octane rated fuels will lower your gas mileage in modern engines as they have octane sensors to adjust the programming. Higher octane rated fuels resist detonation further and therefore provide more powerful detonation with the same energy. The difference in my wife's GMC terrain is 2-3 mpg, but this does not come close to covering the cost difference between premium and regular.

When I was running e85, the power gains were large. My gas mileage dropped, but the price was a lot lower compared to premium. It was about a wash for price, but I had my nice power gains.
 
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