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Mileage - Regular vs Premium

70K views 55 replies 23 participants last post by  Mechanicman 
#1 ·
Just thought you guys might like to know.... I drove from Raleigh, NC to Olivet, MI and back last weekend. Burned Premium gas all the way up and Regular gas all the way back.... Got 23.3 mpg on Premium and 23.7 on Regular....

Go figure,,,, better mileage on Regular?

Don't understand it but I'm switching my car over to Regular since it's cheaper and doesn't seem to cause any problems...
 
#6 ·
It shouldn't cause any damage. The engine has a knock sensor and the computer will retard the timing to compensate for the lower octane. BUT when that happens, you lose performance. So it is a trade off.
 
#3 ·
Just the wind or a very subtle slope will cause your mileage to vary, so you will need to know that information before you can surely confirm the mpg.

The MDX uses 11:1 compression which is a lot higher than most other V6's. The latter means that it needs to use premium to avoid pre-detonation of gas mixture inside your cylinders. If you are driving without exerting the engine, then the knock sensors can help avoid engine damage, but if you are towing or you are racing your engine, then the knock sensors will not be able to compensate and you can have engine damage.

At high revolutions, engine pre-detonation can destroy your engine..

When pre-detonation occurs before the piston gets to the top compression position(compression stage), the gas expansion forces push the piston straight down against the piston axis/engine components instead of converting the gas expansion forces into mostly purely rotational power. The former can completely damage your engine since your engine cannot compress ignited gases that are expanding and engines are not design to handle those pressures/forces.

I will only use regular in extreme circumstances in which the engine load is light and lower RPM's are used..
 
#13 ·
Thanks to all of you for your advice and concerns....

Unlike some of those who responded to this thread I simply drive the car... It is not a truck that hauls 1000s of pounds of stuff, I never use full acceleration, I never go off-road and I never tow anything with the car.... The car normally has one only a driver plus occasionally my wife. I drive it approximately 70% of the time on the freeway at legal limits and always use the cruise control so it just lopes along at 2100 rpm.. Bottom line, I really need about 150 horses and since I have 300 the car is NEVER under stress....

You might also be interested to know that this is not my first rodeo with Regular vs Premium.... I performed the exact same test on my wife's Lexus and found that it got 2.5 mpg better mileage when using Premium so we always burn Premium gas in her car.

I also drove a Nissan Maximum for 125000 miles with no problems on Regular gas.

And lastly, I have built more than one sports car with very high compression engines (14 to 1 and higher) that required leaded racing gas to keep them from pinging so I understand both what pinging is and what damage it can cause.

Bottom line is I don't expect any problems with the MDX since I don't do anything that would stress the engine and might require it to really work (even for a short period of time).

Since I keep my cars for at least 100000 miles or 8 years (whichever comes first) - - I'll update you in 2019 to let you know if I had any trouble.
 
#14 ·
Bottom line is I don't expect any problems with the MDX since I don't do anything that would stress the engine and might require it to really work (even for a short period of time).
I typically do not respond to posts like this, but is it really worth maybe $3.00 per tank fillup over the price of regular (at least here in Southern California) to test your expectations over the recommendations of Acura? I don't understand the logic when I assume you spent $40K+ on the MDX in the first place.
 
#16 ·
The reason that premium fuel is required in the MDX is because that's how the engine horsepower and torque figures were certified. This is the identical engine as used in the Pilot. The Pilot engine uses regular grade gas, but the advertised horsepower and torque are less. The Hyundai Genesis publishes both regular gas and premium gas engine ratings to get around this problem. Too bad Honda doesn't do the same for this engine.

It is interesting to note that there is a note in the Pilot's Owner's Manual that advises using premium fuel when towing a trailer.
 
#20 ·
Acura's engine has a red line of 6700 rpm compared to 6300 on the Pilot, and the Acura engine is 3.7 liters and the Pilot's is 3.47 liters.

At higher compression ratios, rpms, and heat, lower octane gasoline spontaneously explodes more easily, even without a spark, causing pinging/knocking. You will need to be running way below the RPMs/load specs of the Honda Pilot to avoid engine damage, with the Acura engine.

Just imagine your engine piston at the compression stage. It is on his way up and suddenly the low octane gas ignites/explodes before it reaches to the top. That means that the expanding gases are pushing the piston and rod backwards, while the piston is trying to compress the expanding gases in a forward motion.

Then, since the engine is going at high RPM's rotating forward with a lot of rotational inertia, the piston/engine-head/rods/crankshaft will either catastrophically fail or the piston will finish compressing the expanding engine gases. When the piston reaches the top of the compression stage, the piston will be pushing the piston's rod straight down against the crankshaft with huge forces, slowly deforming the metals and materials: i.e. rings, piston, crankshaft, rod, etc.

Compare the latter with a normal engine functioning, where the piston compresses the non-ignited gasoline/air mixture and just when the piston is around the top mark, there is a spark which ignites the mixture, causes gas expansion, and causes the piston to continue to push the rod causing the crankshaft to rotate even faster, in the forward direction, instead of backwards, with the down forces directed to the crankshaft/rod/piston in a way that produces rotational forces, and with all forces magnitudes within the materials designed ranges.

I may be repeating some stuff here, but it may be useful to some younger person who would like to understand how an engine works and how knocking/pinging is caused in these cases.
 
#22 ·
The MDX and identical Pilot engines I was referring to were the early 3.5 liter versions. Back then, to support about a 8 hp difference of rated power, Acura required everyone to use premium gas in the MDX. The engines were exactly the same: bore/stroke/compression ratio/cam, etc.

The current 3.7 liter MDX engine is very different. Just to support a compression ratio well north of 11:1 would surely require premium gas in any engine, except maybe a direct injection version. (BTW, where is Honda's direct injection technology?)

Sorry for the confusion. My daughter isn't the only one who correctly remind me I'm living in the past!
 
#23 ·
Back then, to support about a 8 hp difference of rated power, Acura required everyone to use premium gas in the MDX. The engines were exactly the same: bore/stroke/compression ratio/cam, etc.
Not true. The difference in power between the Pilot and MDX was never as small as 8 hp in the same model year. When the Pilot was introduced in 2003, the MDX had 20 more hp (260 vs 240) and the difference has only increased since then; it's now up to 50 (300 vs 250).
 
#28 ·
Lots of great info here. Maybe this should be a sticky, im sure there're many people out there that can benefit from this thread. Just my two cents...
 
#30 ·
Just for the record, I have used nothing but Shell premium gas since new. Who am I to tempt fate?
 
#31 ·
He is talking about older mdx.

2006 Mdx 10:0:1 3471 displacement. 253@5800 HP, 250 @ 3500 Torque.

2009 Pilot and up. 10:5:1 3471. 250 @ 5700, 253@ 4800.

So yea Newer Pilot get identical engine from older mdx.
 
#33 ·
As you can see 2006 Mdx engine produce 253 HP, and 2009 Pilot engine produce 250 HP. The difference is only 3 HP. but 2009 pilot engine have 3 extra torque than 2006 mdx.

I would say acura engine use preminum gas to gain extra HP.
 
#39 ·
Well, read through all this and I guess I'll throw my two cent, I'm not trying to jab anyone.
It so funny when someone has a car over $40k and it stated on the manual that it only take premium gas and went ahead and fill up with unleaded to saves a few $$.
On the other hand I see people with car that does not required premium gas and they end up using premium gas on their below $40k car.

Luxury car that required premium gas ended up using unleaded gas (Why buy a car that take premium gas and end up using regular gas, I don't get it)

Regular car that uses regular unleaded end up using premium gas (I could understand for some reason like engine knock, beside that why waste $$ when it uncalled for.

You get the picture.
 
#40 ·
Just thought you guys might like to know.... I drove from Raleigh, NC to Olivet, MI and back last weekend. Burned Premium gas all the way up and Regular gas all the way back.... Got 23.3 mpg on Premium and 23.7 on Regular....

Go figure,,,, better mileage on Regular?

Don't understand it but I'm switching my car over to Regular since it's cheaper and doesn't seem to cause any problems...
FYI .. the biggest delta with gas is the ethanol factor. Thats prob why you experience differences between the gas fillups may be ethanol related.
It's because ethanol attacks water vapor like a sponge.
It can really reduce power, mpg, and increase engine life problems.
Before you switch to regular 89 or 87 octane ... check out the effect of ethanol and its varability on performance, mpg, and cost.
If you have 93 Premium in your area ... you can mix that with Plus at 89 octane and have 91 octane in your tank.
It would be wrong to assume anyones Premium and ethanol is water free.
MDX is best with 91 + but 93 alone is overkill by 2 octane.
Mixing 93 w 89 equals 91 and mixing reduces ethanol water problems.
 
#41 ·
Mixing 93 w 89 equals 91 and mixing reduces ethanol water problems.
Oh please! Aside from the variability of octane that you're going to get by mixing, and aside from the PITA that it will be to pump small amounts from multiple tanks, mixing different octane levels does not change the ethanol levels. If you're not having problems using oxygenated fuels with premium fuel (and you shouldn't be), using the wrong fuel isn't going to make any difference. And if you ARE having problems using oxygenated fuels, there's something wrong with your car and you need to get it taken care of.

Sheesh, the misinformation that gets posted... :rolleyes:
 
#45 ·
Test Completed - - Switching back to Premium



- - - - - - - -

OK, the test is complete and - - I've switched back to Premium.....

No problems when using Regular (especially on the highway) but after six or seven tanks of regular in town I notice a 'lack of pep' when accelerating from a stop and significant 'transmission lag' when the car downshifts for a hill at 'in town' speeds (30 to 45 miles per hour).

Switched back to Premium fuel yesterday and find that the car is much more comfortable/enjoyable to drive....

JJ
 
#46 ·
Modern day cars adjust to lower octane quite well and do not adjust to higher octane. But you will get lower pep as you stated w lower octane.
If you have 93 prem in your area you can mix w 89 plus and meet MDX's required 91.
It won't say you a lot but it does reduce ethanol water effect and detergent gums.
 
#48 ·
Modern day cars adjust to lower octane quite well and do not adjust to higher octane. But you will get lower pep as you stated w lower octane.
That's true of some Acura vehicles, but not the MDX. I own other Acura vehicles in which the owner's manual states that you can use lower-than-premium octane without damaging your car, but your performance will suffer. The MDX is different, and the owner's manual states that you should not use lower-than-premium octane, period.

Also, there's no advantage to using lower-than-premium octane, either. Because the MDX is designed for premium, it's not only the acceleration that suffers with lower octane, but also your gas mileage; the difference will wipe out any savings on the price of gas.

You can damage your car's engine by using fuel with octane less than 91, and you won't be saving any money either. DON'T DO IT. Just stick to premium.
 
#47 ·
Just a quick question on your octane experiment. Was the regular gas that you used a ethanol mix or plain regular gas.

I for my MDX try my best to never use ethanol gas. If i am in a bind, i'll put a few gallons till i can get to another gas station.
Ethanol gas offers less oomph.. (for lack of a technical word) and lower gas mileage.
 
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