What fuel grade?

D

dedmiston

Member
When we picked up my wife's CX-9, the dealership told us to use 87 fuel. In our owner's manual there was a loose page recommending 91. I couldn't tell if that page even belonged in there. What grade does everyone else use?
 
I've been using 87 octane for the 2 1/2 months (just hit 3000 miles). No problems to report. The CX-7 requires premium gas because the engine is turbocharged. (One of the main reasons I didn't buy one)
 
87. It's a significant selling point of the CX-9 relative to, say, MDX.
 
Using regular and it runs fine.
Tossed in Premium a few times to see if there was a difference besides my pocket being lighter.
 
I just re-read that page in the manual (duh!). The page says that the manual originally said to use 91, but that you only have to use Unleaded Fuel. Sounds like the marketing team lynched the engineering team and rewrote the playbook.
 
This is right off of the Mazda USA website:

Engine type 3.7L V6 DOHC 24 Valve engine
Horsepower, SAE net 273 @ 6250 rpm
Torque, SAE net 270 @ 4500 rpm
Displacement (cubic inches/cc) 213.3/3496
Bore x Stroke (in/mm) 3.64 x 3.41 / 92.5 x 86.7
Compression ratio 10.3
Recommended fuel 87 Octane
Redline 6450
Engine block material Aluminum
Cylinder head material Aluminum
 
When I mentioned to my salesperson that I have always put premium fuel in my cars, he said it wasn't recommended to do that in this engine because it would make it run hotter.

No idea if that is true or not...so I wonder if midgrade would be ok? There are other considerations other than cost when selecting fuel...emissions for one.
 
carpet_pissr said:
When I mentioned to my salesperson that I have always put premium fuel in my cars, he said it wasn't recommended to do that in this engine because it would make it run hotter.

No idea if that is true or not...so I wonder if midgrade would be ok? There are other considerations other than cost when selecting fuel...emissions for one.
Click to expand...

The CX-9 only calls for 87 octane. Most articles you read say that if you use any fuel with a higher octane than recommended you will just be wasting money.
 
running hotter for wintertime will actually help with the gas milage.... but you pay for more money for premium gas... so probably not worth it
 
Someone want to explain why they think premium gas would make it 'run hotter'? There's no more energy contained in 91 than there is in 87...only added combustion inhibitors to prevent detonation in certain situations.

Higher octane gas can be used when you encounter knocking in high altitude or high temperature situations where regular unleaded is pre-detonating, or where turbocharging / supercharging is causing pre-detonation. End of story.
 
Just bought the CX-9 Grand Touring and the manual has a loose addition to it stating that, the "manual SAID, NOW it SAYS...recomended oct. is 87"

I know they changed the engine to a 3.7L so maybe this is why?
 
I have ran 89 since I purchased the 9. It is a 2007 3.5l. I have ran 87 the last few tanks and it feels it has more low end torque. Ill see if I get better gas mileage. So far average city/hiway is 19.5.
 
actually I worked for Mazda and if the manufacturer recommends a certain octane its because thats what vehicle lasted longest with and performed best with. The engines were designed to run on 87 octane and higher octanes will actually cause carbon build up and engine knock. It does not make your car run faster or better.
 
Does the compression ratio come into play at all? With a compression ratio of 10.3:1, I would think you would want to run 91 or higher. Not that I have switched to 91 or higher on the CX-9, but my Outback with a 10:1 CR is being run on 93 octane (premium or super in TX). Doesn't run hotter...getting a bit better gas mileage and seems a bit more responsive.

Couple of links talking about CR and Octane level

http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html
http://www.tunacan.net/t4/tech/cr.htm
http://auto.howstuffworks.com/question90.htm
http://en.wikipedia.org/wiki/Compression_ratio
 
Last edited:
GrayZoom said:
Does the compression ratio come into play at all? With a compression ratio of 10.3:1, I would think you would want to run 91 or higher. Not that I have switched to 91 or higher on the CX-9, but my Outback with a 10:1 CR is being run on 93 octane (premium or super in TX). Doesn't run hotter...getting a bit better gas mileage and seems a bit more responsive.

Couple of links talking about CR and Octane level

http://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html
http://www.tunacan.net/t4/tech/cr.htm
http://auto.howstuffworks.com/question90.htm
http://en.wikipedia.org/wiki/Compression_ratio
Click to expand...

the direct port injection system used on the new 3.7L motors gives the the car more flexibility on the fuel grade that you can use. being that the fuel is directly injected into the already compressed combustion chamber, it is less prone to detonation. less time for the fuel to heat up and prematurely combust.

with other motors not using direct port injection, the gases are mixed with air in the intake manifold, and compressed together in the combustion chamber. the high compression produces a lot of heat and possible premature combustion due to low fuel grade. so for these motors, high octane fuel is recommended to avoid detonation.

thats why i think mazda feels free to recommend low fuel grade for this car as opposed to other vehicles with high compression ratios.
 
Well, I've 2008 CX-9 (3.7L) and it's pumped with 95 RON. The manual book print as follow:

Fuel requirements​
Vehicles with catalytic converters or oxygen sensors must use ONLY UNLEADED FUEL which will reduce exhaust emissions and keep spark plug fouling to a minimum.

Your Mazda will perform best with fuel listed in the table.
Fuel Research Octane Number
Regular unleaded fuel 90 or above

Fuel with a lower rating could cause the emission control system to lose effectiveness. It could also cause engine knocking and serious engine damage.

I'm in the middle east, and there's only two unleaded fuel type available: 91 and 95. I assumed 3.5L CX-9 might have been recommended to use 89 RON in US for price reason. I might be wrong.
 
FikseRxSeven said:
the direct port injection system used on the new 3.7L motors gives the the car more flexibility on the fuel grade that you can use. being that the fuel is directly injected into the already compressed combustion chamber, it is less prone to detonation. less time for the fuel to heat up and prematurely combust.

with other motors not using direct port injection, the gases are mixed with air in the intake manifold, and compressed together in the combustion chamber. the high compression produces a lot of heat and possible premature combustion due to low fuel grade. so for these motors, high octane fuel is recommended to avoid detonation.

thats why i think mazda feels free to recommend low fuel grade for this car as opposed to other vehicles with high compression ratios.
Click to expand...

The 3.5/3.7 engine family (Cyclone) has been designed to eventually have direct injection however, no direct injection versions of these engines are yet on the market. The first directed injected version is expected to be offered in the '09 Lincoln MKS. I believe you're confusing port injection (manifold) with direct injection (cylinder).

The MazdaUSA website states 87 octane fuel for the 3.7 and the 3.5 also recommends 87 octane. Ford has a comparable recommendation for their vehicles as well. The Cyclone is a very advanced engine design and can run on lower octane fuel while still having a higher compression ratio.

See link: http://www.mazdausa.com/MusaWeb/displayPage.action?pageParameter=modelsSpecs&vehicleCode=CX9

Ted
 
Last edited:
kosh2258 said:
The 3.5/3.7 engine family (Cyclone) has been designed to eventually have direct injection however, no direct injection versions of these engines are yet on the market. The first directed injected version is expected to be offered in the '09 Lincoln MKS. I believe you're confusing port injection (manifold) with direct injection (cylinder).

The MazdaUSA website states 87 octane fuel for the 3.7 and the 3.5 also recommends 87 octane. Ford has a comparable recommendation for their vehicles as well. The Cyclone is a very advanced engine design and can run on lower octane fuel while still having a higher compression ratio.

See link: http://www.mazdausa.com/MusaWeb/displayPage.action?pageParameter=modelsSpecs&vehicleCode=CX9

Ted
Click to expand...
thanks for the correction.....

i guess its not direct injected....

so i guess after that is said, we can atribute the lower fuel grade to less aggressive tuning by retarding the timing and increasing air/fuel ratios
 
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