Switched Fuel from Shell to Costco and Noticed Something Strange

[Miker]

So I have been running Shell regular in my Mustang since I bought it. No issues like knocking that I could here. Car is a Stage 1 Roush so it does have their mufflers but I don't believe any kind of modified tuning so regular is appropriate.
My last tank of fuel was from Costco which is also a top tier rated fuel. I have now twice noticed that my temperature gauge has risen about an 1/8 inch above center on the freeway in 5th on cruise with the AC on. It was hot out over 100 but I have driven the car many times in hotter temps and had never seen the gauge rise. The needle usually rides about a needles width below center. The first time I was pulling a pretty good hill and it was probably 3 needle widths above the center.
Oil is at the top mark and the coolant level is spot on.
Anyone else notice anything like this? I am going to switch back to Shell next tank and hopefully it will stop happening.

 

[07 Boss]

Only effect fuel would have on operating temps is if it was running leaner than usual. Unless it has more ethanol in it then it may burn a little hotter but with less power. If you are truly running hotter your fuel mileage should show a decrease because more energy is being converted to heat rather than making power.

 

[dark steed]

Did Roush put actual sensors and gauges in their cars as opposed to the normal “glorified idiot light” gauge in the 05-09 models?
Because they show the exact same temp until it gets over a certain voltage from the sender and then it goes to full hot…


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[RocketcarX]

Costco is inferior to Shell, no reason to switch. I don't have to know anything about Costco's fuel to say that.
Your vehicle is boosted, it needs tier 1 premium fuel with the right additive package.

 

[WJBertrand]

I’ve used both Costco and Shell many times in my ‘13 GT. It has a Ford Racing Performance Products ProCal tune, so I have to use premium. I’ve never noticed any difference in the way it runs on either fuel. The same goes for our regular grade burning Rav4. No difference in fuel mileage between them either.

Seems like you should probably use premium given that your car is tuned, especially if it’s also boosted! I’ve never heard of running a boosted car on regular. Kinda defeats the purpose, no?

 

[Miker]

The motor is not tuned or boosted. Stage 1 Roush cars only have the axel back Roush mufflers and tips.
Costco on the pump has a notice stating their fuel contains at least 10% ethanol. I believe that here in CA the fuel has to have at least 10% ethanol. I read that ethanol will make your engine run hotter like 07 boss said because it has to work harder. Also my understanding is that the gauge in our cars is not the idiot light type and will register and move with engine temperature changes. When I noticed it pulling the hill I down shifted to 4th and the needle slowly moved back to its normal position.

 

[86GT351]

Something to know about Generic stations selling fuel. It is still name brand fuel. The main players have millions of gallons of fuel to move within a specific time. Most goes to there own stations. The rest gets sold to the independents at auction. They buy it at a discounted price so they can generally sell it slightly less expensive. It is still good fuel.

 

[JC SSP]

86GT351 has spoken the truth. Wife used to be the CFO of a large petroleum company and this was the norm.

Regardless if it is she’ll chevron or mobile the grade 87, 89 and 93 it’s all the same gas.

Might be different in California, seems like that’s common out there…

 

[WJBertrand]

All of our fuels in California are mandated to be E10 minimum, so Shell and Costco will both be 10% ethanol.


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[86GT351]

All of our fuels in California are mandated to be E10 minimum, so Shell and Costco will both be 10% ethanol.


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Right. But just because the rating is there does not verify it is in fact 10%. only way to verify is sample test.

To the OP. If the car was in fact running leaner that could be the factor. However, I personally don't think it was the gas

 

[Miker]

Right. But just because the rating is there does not verify it is in fact 10%. only way to verify is sample test.

To the OP. If the car was in fact running leaner that could be the factor. However, I personally don't think it was the gas

I know but the fuel is the only thing that changed.

 

[JC SSP]

What about the ambient air including heat index... the past 2 week have been scorchers...

Here in FL 96-98 with 105-106 heat index. Hottest ever...

Still not hotter than Mali, Sengel, Djibouti or Afghanistan... LOL

 

[86GT351]

I know but the fuel is the only thing that changed.

So then maybe it's a bad tank of gas? Not the specific brand

 

[86GT351]

What about the ambient air including heat index... the past 2 week have been scorchers...

Here in FL 96-98 with 105-106 heat index. Hottest ever...

Still not hotter than Mali, Sengel, Djibouti or Afghanistan... LOL

Come on man. Temp her is fun to deal with this time of year.

 

[JC SSP]

My boosted Audi looses about 50HP in this heat. Lol

 

[WJBertrand]

Costco is inferior to Shell. I don't have to know anything about Costco's fuel to say that.

Now that’s funny right there…[emoji1787]


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[MrBhp]

I was on the "Shell is great gas" wagon at one time. I got a "bad tank" at Shell in the Shelby while out on a run to the Hill Country. Half throttle would cause knock. That was the last tank of Shell fuel that will ever go in my car. I started using Sam's Club 93. I picked up a solid and consistent 2 tenths at my local strip.
And no, generic stations don't have a giant generic refinery at their disposal. I've worked on pig launchers at loading terminals for days at a time. Terminal was being supplied by Motiva (Shell), Mobil, Chevron. I watched every brand of tanker truck pick up loads of fuel straight from the teet. Three refiners delivering product to the terminal, maybe a dozen different brands picking up, plus all the generic tankers of no recognizable brand. I've used Costco 93 as well. No noticeable difference.

FWIW
There is no way I would run regular in my car. The 4.6 3v has a fair amount of CR so it likes octane. Regular is not going to hurt your engine, unless Roush tuned for premium. Which I think they did.

 

[Miker]

Ok I am going to switch to Premium at Costco. Their premium is the same price as the Shell Regular. Plus there whole setup is new so their tanks should be free from most gunk.
I remember when I bought it the son of the owner said he thought that his parents ran premium in it. Is there any way to verify if the stock tune has been modified?
Also I have always believed if you run premium in an engine that is designed to run on regular that the engine would develop more carbon build up do to an incomplete burn.

 

[JC SSP]

Put a can of EFI cleaner in there too.

 

[Laga]

Also I have always believed if you run premium in an engine that is designed to run on regular that the engine would develop more carbon build up do to an incomplete burn.

The ONLY difference the octane rating makes in gasoline is its resistance to detonation. Detonation is defined as a second spontaneous source of ignition AFTER the spark. All levels of octane pump gas burn at the same rate, temperature, and contain the same amount of energy. With all else being equal. It’s once you get into race fuel that the characteristics of the burn changes.