Gasoline grades

[TerryMU]

I have a 2005 Murano. Will it harm the engine if I switch from middle to premium grades at certain times. I ran some premium in it once and it seemed to improve the performance (at a price), but I had just bought the car so I really couldn't judge the change. I haven't tried it since, because it runs so well.

[67hat34c]

No:

Octane is a measurement on how fast gasoline burns. Lower octane burns faster than high octane.

When you engine compresses the fuel/air mixture in the cylinder it gets very hot. Low octane gas will light faster and earlier than high octane. In cases with high compression engines this means it can light before the spark plug fires and this causes the pinging noise that over time can ruin your engine.

For the modern engines with knock sensors among a host of other sensors and Computer controlled ingnition and fuel delivery the octane is not that important. Your computer will adjust the timing and fuel delivery to match the fuel you have. Now in cases with low octane, the computer will retard the timing and allow for perfect burn but at a price. Retarded timing is less power. Computer will advance the timing for high octane fuel. advanced timing will give you noticable more power.

In you murano you will get slightly better MPG and performance with high octane fuel because of the timing advance the computer gives the engine. I cant tell you if you will save money by buying 87 89 or 93. I always use 93 because I want optimum performance from all my engines.

[Desert Rat]

as long as you're not experiencing detonation (or pinging as it's often referred to), running higher octane gas is a waste of money.

Mine has never faltered running standard 87 octane regular.

[TerryMU]

Thanks for the information.

TU

[whitestar16]

I am going to go against the grain a bit and say it does make a difference and you should be careful in the Murano. Pre-ignition and detonation issues are a direct cause of head gasket failure due to the higher pressures correctly mentioned in the above posts. The comments about the car "adjusting" due to advanced software and engineering may not be correct either. At least not entirely. The car is expensive. Use premium gas would be my recommendation.

[BBISHOPPCM]

This is how I am led to believe the knock sensor works; if a persistent knock (ping) is detected, the ignition is automatically retarded to compensate; this is done on-the-fly, so it's not as though it reprograms itself every (xx) minutes, it just retards on an as-needed basis. That said, retarded timing reduces output power, as the engine is not running optimally; reduced power equals reduced fuel mileage. Whether there is any long-term damage as a result of lower octane fuel in an engine that was designed at the factory to run primarily on middle grade or premium fuel is debatable, but if you care about fuel mileage and power, stick with 89 or better. Believe it or not, I do notice a HUGE difference with 89 compared to 93. I have never run 87 in my engine, but I might try it sometime to see what happens (preferably when it's ready to trade in!).

[whitestar16]

I am NOT knowledgeable about car engines for the most part. But I do read quite a bit. Here is an excerpt from Wiki on Octane and related stuff to our discussion;

A fuel with a higher octane rating can be run at a higher compression ratio without causing detonation. Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more motive power. Engine power is a function of the fuel, as well as the engine design, and is related to octane rating of the fuel. Power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. When the throttle is partially open, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than when the throttle is opened fully and the manifold pressure increases to atmospheric pressure, or higher in the case of supercharged or turbocharged engines.

Many high-performance engines are designed to operate with a high maximum compression, and thus demand high-octane premium gasoline. A common misconception is that power output or fuel mileage can be improved by burning higher octane fuel than a particular engine was designed for. The power output of an engine depends in part on the energy density of its fuel, but similar fuels with different octane ratings have similar density. Since switching to a higher octane fuel does not add any more hydrocarbon content or oxygen, the engine cannot produce more power.

However, burning fuel with a lower octane rating than required by the engine often reduces power output and efficiency one way or another. If the engine begins to detonate (knock), that reduces power and efficiency for the reasons stated above. Many modern car engines feature a knock sensor – a small piezoelectric microphone which detects knock, and then sends a signal to the engine control unit to retard the ignition timing. Retarding the ignition timing reduces the tendency to detonate, but also reduces power output and fuel efficiency.------------------------------------------------------------------------

I also read a very good article on pre-ignition and detonation and engines that I have no problem finding the link for if there is any interest. The bottom line is that I don't personally care all that much about fuel efficiency and my Murano. I have a Honda Civic Hybrid as an alternate car that usually gets 50 MPG or greater. I care a lot about engine problems in the Murano however and thus anything that could contribute to engine issues in this car gets my attention based on the whole head gasket and valve cover problems that get reported on in the various forums. IMMV.

[kelly7898]

I am NOT knowledgeable about car engines for the most part. But I do read quite a bit. Here is an excerpt from Wiki on Octane and related stuff to our discussion;

A fuel with a higher octane rating can be run at a higher compression ratio without causing detonation. Compression is directly related to power (see engine tuning), so engines that require higher octane usually deliver more motive power. Engine power is a function of the fuel, as well as the engine design, and is related to octane rating of the fuel. Power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. When the throttle is partially open, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than when the throttle is opened fully and the manifold pressure increases to atmospheric pressure, or higher in the case of supercharged or turbocharged engines.

Many high-performance engines are designed to operate with a high maximum compression, and thus demand high-octane premium gasoline. A common misconception is that power output or fuel mileage can be improved by burning higher octane fuel than a particular engine was designed for. The power output of an engine depends in part on the energy density of its fuel, but similar fuels with different octane ratings have similar density. Since switching to a higher octane fuel does not add any more hydrocarbon content or oxygen, the engine cannot produce more power.

However, burning fuel with a lower octane rating than required by the engine often reduces power output and efficiency one way or another. If the engine begins to detonate (knock), that reduces power and efficiency for the reasons stated above. Many modern car engines feature a knock sensor – a small piezoelectric microphone which detects knock, and then sends a signal to the engine control unit to retard the ignition timing. Retarding the ignition timing reduces the tendency to detonate, but also reduces power output and fuel efficiency.------------------------------------------------------------------------

I also read a very good article on pre-ignition and detonation and engines that I have no problem finding the link for if there is any interest. The bottom line is that I don't personally care all that much about fuel efficiency and my Murano. I have a Honda Civic Hybrid as an alternate car that usually gets 50 MPG or greater. I care a lot about engine problems in the Murano however and thus anything that could contribute to engine issues in this car gets my attention based on the whole head gasket and valve cover problems that get reported on in the various forums. IMMV.

Thank you for the post.
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[breezy]

Without getting into too much detail I think it has as much to do with the CVT as engine performance. In my 04' I had a "knock" while the engine was under load....low RPM's, accelerating while going up a hill for example. In the 2010, I think the CVTand the Engine match has improved and I'm not getting a knock...thus far.
I will use 89 octane occassionally during highway only conditions...but high octane otherwise.

Later

[67hat34c]

89 is fine. I also would suspect improvement in ECU and TCU software that will adjust engine to prevent knock. Again only draw back is a very slight decrease in performace which most will never notice.

[whitestar07]

The octane rating that is recommended for any motor is based on the compression ratio of that motor. The higher the compression the higher the octane necessary to prevent detonation. If you run high octane fuel in a motor that recommends 87 you may not notice any difference other that the costs. But if you run 87 in a motor that requires high octane fuel you run the risk of the fuel igniting to early and can damage your engine.

Nissan recommends premium grade fuel for the Murano- but does not specify the octane that I have found yet. The issue exceeds just performance consideration in my opinion. Proceed with caution.

[terrycs]

Just use what is recommended in the operator's manual.