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Cadillac XT4 1st Generation Forum (2019+) Discussion, Premium or regular/gas mileage in Cadillac XT4 Forums; So I’ve been putting in regular unleaded. I know it says that Cadillac recommends high test has anyone noticed any ...
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    jf7fsu's Avatar
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    Premium or regular/gas mileage

    So I’ve been putting in regular unleaded. I know it says that Cadillac recommends high test has anyone noticed any difference? I’m hearing about some pretty good mileage from other people my mileage stinks I’m getting around 18 miles to the gallon in the city I live in hot and sunny South Florida. Mostly stop and go driving

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    drvslka's Avatar
    drvslka is offline Cadillac Owners Member
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    Re: Premium or regular/gas mileage

    I'm a big proponent of using premium gas. I haven't recorded numbers to confirm, but based on feel (placebo?) I swear there is a difference. Just feels a little quicker.
    jimmie jam and Marc NY like this.

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    Submariner409 is offline If it won't run, install a sound system
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    Re: Premium or regular/gas mileage

    Modern PCMs will slightly retard timing - from the full allowed value - based on knock sensor inputs to control "knock" from lower octane fuels than originally specified for that engine. No harm will come to the engine, but the total available "maximum performance" will be reduced a tad. If you don't track or autocross the car you'll probably never feel the difference. If you want to watch timing as a real-time function, use a ScanGauge-II. I monitor actual coolant temp, timing, MAP (inverse manifold vacuum), and intake air temp.

    Prove it to yourself - take the car to the local dragstrip (not the street) for a couple of Friday evening Test And Tunes. First time, run your 87 or 89 standard fuels, less than 1/2 tank (weight) and keep the timeslips. Then, when the tank is really low, dump in 6 or 7 gallons of 91/93 and run again. The timeslips - NOT hearsay or butt dyno guesses - are proof of your performance changes.

    All gasolines are the same cleanliness and detergency additive "quality", refinery wise. The different anti-knock additives are what make it "premium" or "regular". Premium fuels have a slower flame front travel in order to keep the burn in the piston downstroke for longer periods, slightly increasing power.

    Run a TopTier gasoline - Google it.
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    Marc NY's Avatar
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    Re: Premium or regular/gas mileage

    Is it really worth the savings???

    The difference in the price of gas is .30 in our area. If you use one tank of gas a week or (20 Gallons) that would be $6.00 a week x 52 weeks you are talking about approximately $312.00 a year in added costs. Not very much savings to make me want to switch to regular gas... plus with premium gas you will get better performance and mileage.
    jimmie jam and drvslka like this.

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    terrymazza is offline Cadillac Owners Member
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    Re: Premium or regular/gas mileage

    I burn only premium and am getting between 28 and 30 MPG. My best was 34 one time only. Have 7000 on the clock so far. Longest trip was to/from Florida and Wisconsin.

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    Re: Premium or regular/gas mileage

    Quote Originally Posted by terrymazza View Post
    I burn only premium and am getting between 28 and 30 MPG. My best was 34 one time only. Have 7000 on the clock so far. Longest trip was to/from Florida and Wisconsin.
    Those are some great numbers in my book!

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    marktanner is offline Cadillac Owners Enthusiast
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    Re: Premium or regular/gas mileage

    Ambient temps also play a role. High ambient temps will cause the timing to be pulled more than with cooler temps. At high temps with the AC on, one can sometimes hear the pinging. Premium is usually a good idea under those circumstances. Cool/cold temps without the AC compressor will do quite well even on regular, and Premium may not affect the performance at all. I'm not sure it's ever cool enough in South Florida to make regular performance equal to premium, but up north in the winter, for most cars premium would be unnecessary. However, when it says Premium is required, all bets are off.

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    Brewster100 is offline Cadillac Owners Member
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    Re: Premium or regular/gas mileage

    I use 'Premium' - and they have what they call 'TOP TIER' suppliers that they want you to use. In general Marathon or Exxon are the brands I use. I'm showing 'best average' of 27.4 but have not taken on long trip yet. Like Submeriner posted- the PCM will adjust and 'retard' timing if any knock is detected.

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    BlackDeVille is offline Cadillac Owners Fanatic
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    Re: Premium or regular/gas mileage

    I have 3000 miles of mostly stop and go local driving. Have only used premium and lifetime average is just over 24. Have gotten as high as 28 on a long trip with average speed over 70mph. I'm very happy with the mileage and performance of this vehicle.

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    Re: Premium or regular/gas mileage

    The question of premium and its need, use, value etc needs a global sticky. Seems to be a reoccurring topic across multiple forums.

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    Submariner409 is offline If it won't run, install a sound system
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    Re: Premium or regular/gas mileage

    It's always a topic of discussion - hearsay, black magic, poor advice, "my friend told me", and snake oils seem to win out over fact with great regularity - in every car forum.

    I work part-time at our local Western (Tire &) Auto shop - behind the parts counter. I simply LOVE to sell snake oils in quantity to the ricer crowd.

    Google "spiff". Those guys ^^^ pay all of my monthly gasoline bills.

    Google "cadillac forums premium or regular gasoline use".

    A little knowledge is a terrible weapon.

    A motor vehicle will always get its best fuel economy - octane regardless - if you drive with an egg between your foot and the gas pedal. The same car​ will get radically different economy figures when driven in the city, suburban/rural, or highway environments. Fact.
    jf7fsu likes this.

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    Re: Premium or regular/gas mileage


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    Marc NY's Avatar
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    Re: Premium or regular/gas mileage

    Not using Premium gas when a manufacture recommends it may void your warranty.

    https://www.cars.com/articles/if-pre...1420684149253/

    *NOTE: Below is a cut and paste of only a small section of the above article.

    What If the Manufacturer Requires It?

    When a vehicle manufacturer requires using premium fuel, it is because that particular vehicle’s fuel system is designed to work best with higher octane gas. Using regular gas in an engine that requires premium could void your warranty. That is most likely to happen if using regular causes severe engine knock or pinging (premature ignition of the fuel, also known as detonation) that damages the pistons or other engine parts. Using the wrong gasoline may cause other problems, like decreased fuel economy and engine performance.

    For example, here is what GM says about the subject in an owner’s manual for a vehicle that requires premium:

    “Use premium unleaded gasoline with a posted octane rating of 91 or higher. If the octane rating is less than 91, you could damage the engine and may void your vehicle warranty. If heavy knocking is heard when using gasoline rated at 91 octane or higher, the engine needs service.”

    Note that this applies only to engines that require premium gas. Some manufacturers recommend premium gas but say that regular or mid-grade gas can be used instead. They usually warn that using lower-octane gas could reduce performance and fuel economy. When that happens noticeably, or if engine knock occurs, they advise to start using premium.

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    My manual says “recommended” not required.

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    Marc NY's Avatar
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    Re: Premium or regular/gas mileage

    Quote Originally Posted by jf7fsu View Post
    My manual says “recommended” not required.
    Since I do not have my XT4 yet I don't have a owner's manual to go by. If it indeed says "recommended" (and yes I do believe you) then depending on your circumstances it is certainly an available option. IMO: I still feel for the little extra cost to use Premium gas is approximately ($312.00 more a year) I will most likely use it.

    To add one more article, I came across here is another link to review if you like. Again, it may bolster your own personal feelings on whether you will want to use Premium or save $$ and use Regular gas.


    https://money.cnn.com/2017/12/12/aut...udy/index.html

    The term "Premium" gas is a little misleading. You may think it's better than "Regular" gasoline because, well, it is called "Premium" and it costs more.

    Really, it's just a slightly different formulation made for engines that operate at higher pressures and, therefore, require a more stable fuel. In an engine that's engineered to run on lower-octane Regular gas, using Premium doesn't make one bit of difference, except on your credit card statement. It costs about 50 cents more per gallon, according to AAA. (approx. .30 in my WNY area)

    In many cars and SUVs, Premium gasoline is "recommended," but not "required." Engineers at AAA set out to see whether using Premium gas instead of Regular really makes a difference in these cars.
    The answer: It makes a little difference in performance and fuel economy but not much. Still, there are circumstances where it makes sense to pay for it in these vehicles.
    AAA tested Premium and Regular gasoline in six vehicles: a Ford (F) F-150, a Cadillac Escalade, a Mazda Miata, an Audi A3, a Ford Mustang GT and a Jeep Renegade.

    On average, the vehicles got 2.7% better fuel economy when running Premium gas. But that's just an average. The results varied from a 7.1% improvement in the big Escalade SUV to a 1% decrease in fuel economy in the small Audi A3.
    hat means fuel savings are not enough to offset the cost difference between Regular and Premium gas.

    According to AAA's test, it would cost about $300 more to run a Cadillac Escalade on Premium for a year, based on EPA fuel economy estimates and national average gas prices.
    Still, you might want to spring for Premium sometimes, said Bill Studzinski, a fuels expert with General Motors (GM), the company that makes the Escalade. It will run just fine on Regular under most circumstances, he said. But under extreme conditions, such as when towing a trailer or driving in extremely hot weather, using Regular could lead to damage.

    AAA also says that if you hear knocking or pinging sounds in your engine, consider that the sound of your car asking for the more expensive fuel.

    AAA also looked at horsepower output. On average, vehicles produced 1.4% more horsepower using Premium. It made the biggest difference in the V8-powered Mustang GT, which generated 3.2% more power using Premium. But the Jeep Renegade actually produced slightly less power when running on Premium.

    In some cars, usually luxury models, Premium fuel is actually required, not just recommended. These vehicles could sustain damage from prolonged use of Regular gasoline. But most engines are designed to run on Regular all the time. In those engines, using Premium fuel won't hurt anything, but it also won't improve anything, either.

    In any event, to save money on gas and prevent straining your engine, follow the recommendations in the owner's manual.

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