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Discussion Starter · #1 ·
I have been having some issues over the past few weeks with my cruze. I will get random times, usually extended periods of time where my car will have bad mpg 10-20 at best( usually 45-55 mpg) and awful power, for example today I floored it on the highway for about ten seconds and the car went from 68mph to 71mph. The most common thing I’ve seen during my search for an answer is people filling up their gas, this is happening around the time I do that but also other times as well, like when the tank is half empty. I consistently use the same gas( ultra or whatever it’s called). Early this year my oil pump blew and I am worried about the engine, wondering if this could be bad compression from a piston. I moved about a month and am driving the car more, so the issue could have been present before and I probably wouldn’t have noticed as the car wasn’t used for more then a five or ten minute drive most days, but I’m driving an hour a day now. Any ideas would be helpful, I do plan to have the dealer look at it as it is still within warranty.
 

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Discussion Starter · #2 ·
More about the car since I kinda forgot, car is a 2014 lt with the 1.4t. Has around 37600 miles, oil pump went around 35,000 miles. I usually use synthetic oil as well but when the pump was rebuilt I believe the dealer put whatever the stock junk is back in it.
 

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The dealer probably put the AC Delco dexos1 oil in. Staring in 2015 or 2016 this became a full synthetic.
 

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Could be a turbo underboost condition putting the car in limp mode. Kinda common for Cruzes.

In this case, there would be a pending code (a CEL needs a condition to happen multiple times).
 

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Yeah,
1- Tires. My new cheapo tires give me about 5-10MPG less on the insta-readouts on the highway than the stock LRR tires; also due to them needing higher PSI than the stockers. (stock 35, new ones at least 42PSI)
2- Fuel type. 91-93 octane fuels give better mpg than regular fuel (87) , especially on hotter days.
3- like mentioned, something in your car might be off. Check the OBD port for error codes.
4- Oil, what your car needs is Dexos certified oil. It's more suited for Turbo cars, and is better in MPG than even the standard synthetic.
While you can use synthetic oil on your cruze, you'll have to change it out more often. Never use regular oil in your car. It can give lubrication issues, and cause parts of the engine or turbo to fail prematurely.
5- Check filters.
 

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Discussion Starter · #8 ·
Could be a turbo underboost condition putting the car in limp mode. Kinda common for Cruzes.

In this case, there would be a pending code (a CEL needs a condition to happen multiple times).
Well I can’t get my hands on a scanner until later this week. Is the underboost condition caused by something specific or is there a way to make it not happen?
 

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Well I can’t get my hands on a scanner until later this week. Is the underboost condition caused by something specific or is there a way to make it not happen?
Highway loads in top gears will usually do it.

Usually a result of a worn wastegate pin on the turbo; could be a result of toasted bearings from the oil pump fiasco. When the ECM doesn't see the boost it's demanding, it flags the underboost code and puts the car in a "safe" mode where it's basically producing no boost at all.
 

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Discussion Starter · #10 ·
Yeah,
1- Tires. My new cheapo tires give me about 5-10MPG less on the insta-readouts on the highway than the stock LRR tires; also due to them needing higher PSI than the stockers. (stock 35, new ones at least 42PSI)
2- Fuel type. 91-93 octane fuels give better mpg than regular fuel (87) , especially on hotter days.
3- like mentioned, something in your car might be off. Check the OBD port for error codes.
4- Oil, what your car needs is Dexos certified oil. It's more suited for Turbo cars, and is better in MPG than even the standard synthetic.
While you can use synthetic oil on your cruze, you'll have to change it out more often. Never use regular oil in your car. It can give lubrication issues, and cause parts of the engine or turbo to fail prematurely.
5- Check filters.
I have brand new continental tires on it, I always use 93 octane from sheetz, and I do use dexos approved synthetic oil. So I don’t think any of that is an issue, the air filter was good last time I checked it a few months ago, I’ll have to check the oil filter, I can’t imagine it being the fuel filter at such low mileage. I’ll check back in once I get it scanned. Thanks for the input everybody.
 

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The cheapo tires I had, were totally different from any other tires I've had.
They had a higher content of silicone in them, making them sticky (thus grip better), reducing road noise, and according to the manufacturer also release heat easier; compared to the conventional rubber tires.
They were very flexible too.
But they had to be pumped up to much higher PSI levels (rated at 50PSI max)
Even at 40PSI they still ran quieter and with worse MPG than the stockers at 35PSI.
The newer ones seem to stretch a bit more; and after setting in, a day later, I had to add about 2-3PSI to them.
I'd check to see if your new tires have such high silicone levels as well, and thus might need more PSI?

On my Eco, the car is very quiet, save for roadnoise.
 
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