high octane fuel
Mudding
Joined: Aug 2007
Posts: 134
Likes: 2
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RE: high octane fuel
Forgive me, but I see so much bunk in these octane/gas threads, that it drives me crazy. Here's my safe rule of thumb.
If your vehicle has a knock sensor, then in most cases you can drop 1 grade without detrimental effects. The vehicle's ECU will compensate, but there is a limit to how much it can compensate, hence the 1 grade rule. You might feel a difference in performance under load or in different ambient conditions (altitude, temp, etc.), but if you're driving around on the road empty and you're equipped with a knock sensor, then have at it. Remember that not all gasolines are created equally, and that the octane rating at the pump is an average of research and motor octane, so two gasolines with identical octane ratings can perform differently.
If your vehicle does not have a knock sensor, stick with the manufacturers recommendation. Using gas with octane lower than recommended can cause detonation or pinging in the engine, and shorten its life. BTW, not all pinging is audible! Using gas with octane rating higher than recommended can cause driveability problems, especially in cold/dry/high alts.
Higher octane does not mean higher quality, it means lower volatility which means it is less likely to combust under pressure without a source of ignition. This means that it is more important for older engines with carbon build up on the cylinder head to stay with the manufacturer's recommendation.
Off the soapbox now. Flame suit on!
If your vehicle has a knock sensor, then in most cases you can drop 1 grade without detrimental effects. The vehicle's ECU will compensate, but there is a limit to how much it can compensate, hence the 1 grade rule. You might feel a difference in performance under load or in different ambient conditions (altitude, temp, etc.), but if you're driving around on the road empty and you're equipped with a knock sensor, then have at it. Remember that not all gasolines are created equally, and that the octane rating at the pump is an average of research and motor octane, so two gasolines with identical octane ratings can perform differently.
If your vehicle does not have a knock sensor, stick with the manufacturers recommendation. Using gas with octane lower than recommended can cause detonation or pinging in the engine, and shorten its life. BTW, not all pinging is audible! Using gas with octane rating higher than recommended can cause driveability problems, especially in cold/dry/high alts.
Higher octane does not mean higher quality, it means lower volatility which means it is less likely to combust under pressure without a source of ignition. This means that it is more important for older engines with carbon build up on the cylinder head to stay with the manufacturer's recommendation.
Off the soapbox now. Flame suit on!
RE: high octane fuel
The knock sensor is there to compensate for the lower quality fuel and for when you work the engine hard, like climbing a hill. Not to compensate for the wrong octane.
Spark knock will happen when climbing a hill with a carburated car, it is normal and expected. The knock sensor keeps that from happening with a fuel injected car.
Vacum advance on a distribtor cap and rotor is also supposed to compensate for that on a carburated car.
If you use the wrong octane gas andthe ECU adjusts for that and then you work the engine hard and there is no more room for adjustment you will damage your engine. Once or twice, no problem. But if you climb a big hill on the way to work everyday 5 days a week...well you said it yourself, you cannot always here the damage being done.
Manufactershave a octane rating for a reason, that is because they have designed AND tested the engine under any and all conditions using the right and wrong octane.
A friend of mine used to be a test driver for AMC motors back in the 70's, 100,000 miles a yearwas average miles on any of their cars. He even got to drive a car for 8 hours at top speed on the oval track.
My point is, theyrequire it for a reason, if it was recommended then that is a totally different story.
My '01 Montero said that premium was "Highly Recommended for maximun engine performance, life and MPG" but that a lower octane would be fine. I always ran premium.
Land Rover requires minimum 91 octane.
It boils down to this, they are your cars you can do what you wish. Just make sure that you inform the poor sap who buys your Rover from you when you sell it that you ran the wrong grade of gas in it so that he knows that he is in for trouble later down the road.
Ok, sorry, that last part was just mean, but we have seen to many people on this forum get screwed because somebodycovered upa problem when they sold them the truck.
Spark knock will happen when climbing a hill with a carburated car, it is normal and expected. The knock sensor keeps that from happening with a fuel injected car.
Vacum advance on a distribtor cap and rotor is also supposed to compensate for that on a carburated car.
If you use the wrong octane gas andthe ECU adjusts for that and then you work the engine hard and there is no more room for adjustment you will damage your engine. Once or twice, no problem. But if you climb a big hill on the way to work everyday 5 days a week...well you said it yourself, you cannot always here the damage being done.
Manufactershave a octane rating for a reason, that is because they have designed AND tested the engine under any and all conditions using the right and wrong octane.
A friend of mine used to be a test driver for AMC motors back in the 70's, 100,000 miles a yearwas average miles on any of their cars. He even got to drive a car for 8 hours at top speed on the oval track.
My point is, theyrequire it for a reason, if it was recommended then that is a totally different story.
My '01 Montero said that premium was "Highly Recommended for maximun engine performance, life and MPG" but that a lower octane would be fine. I always ran premium.
Land Rover requires minimum 91 octane.
It boils down to this, they are your cars you can do what you wish. Just make sure that you inform the poor sap who buys your Rover from you when you sell it that you ran the wrong grade of gas in it so that he knows that he is in for trouble later down the road.
Ok, sorry, that last part was just mean, but we have seen to many people on this forum get screwed because somebodycovered upa problem when they sold them the truck.
Mudding
Joined: Aug 2007
Posts: 134
Likes: 2
From:
RE: high octane fuel
ORIGINAL: Spike555
The knock sensor is there to compensate for the lower quality fuel and for when you work the engine hard, like climbing a hill. Not to compensate for the wrong octane.
The knock sensor is there to compensate for the lower quality fuel and for when you work the engine hard, like climbing a hill. Not to compensate for the wrong octane.
Spark knock will happen when climbing a hill with a carburated car, it is normal and expected.
The knock sensor keeps that from happening with a fuel injected car.
Vacum advance on a distribtor cap and rotor is also supposed to compensate for that on a carburated car.
If you use the wrong octane gas and the ECU adjusts for that and then you work the engine hard and there is no more room for adjustment you will damage your engine. Once or twice, no problem. But if you climb a big hill on the way to work everyday 5 days a week...well you said it yourself, you cannot always here the damage being done.
Manufacters have a octane rating for a reason, that is because they have designed AND tested the engine under any and all conditions using the right and wrong octane.
Vacum advance on a distribtor cap and rotor is also supposed to compensate for that on a carburated car.
If you use the wrong octane gas and the ECU adjusts for that and then you work the engine hard and there is no more room for adjustment you will damage your engine. Once or twice, no problem. But if you climb a big hill on the way to work everyday 5 days a week...well you said it yourself, you cannot always here the damage being done.
Manufacters have a octane rating for a reason, that is because they have designed AND tested the engine under any and all conditions using the right and wrong octane.
Look, I understand your "better safe than sorry" approach, but in this age of $4.00 gal gasoline it is legitimate to ask if we are throwing money away. I can assure you a lot of folks use premium unnecessarily.
Rock Crawling
Joined: May 2008
Posts: 344
Likes: 0
From: Colorado
RE: high octane fuel
The intricacies of modern fuel injection and spark control could fill many many pages.
Use what is recommended or better. Gas, parts, oil, etc...
Saving money on gas is done with the right foot, not a few bucks between tanks.
Happy Roving,
Pete
Use what is recommended or better. Gas, parts, oil, etc...
Saving money on gas is done with the right foot, not a few bucks between tanks.
Happy Roving,
Pete
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