Like other luxury vehicles, the recommended fuel for the RDX is premium grade with EPA of 19/23. Anyone knows what the long term effect on the car's engine of using regular unleaded or unleaded plus in a vehicle that the manufacturer has recommend using premium grade?

 

If you search this site, you'll find other threads discussing this issue.
My two cents is that they recommend premium for a reason and using regular will likely cause problems (long term issues, not immediate failures).

 

I always understood the premium fuel to only be necessary for the advertised MPG and HP (performance).

Joe

 

RDX = turbocharged engine = bad things if you use regular for the long term...

Plus, this has been discussed before...

 

From Previous Thread:
http://www.usatoday.com/money/autos...remiumgas_x.htm

Good Article. I will have to agree with CGTSX2004, you are buying a turbo...why buy it if you will only put Regular in it.

 

.....premium is recommended and regular can be used, you generally get a disclaimer that says that if you use regular you will get reduced performance as well. That "performance" includes fuel efficiency. So the reduced gas mileage will have a bigger impact on your wallet than the measly 16 cents or so additional for premium gas.

For Example gas today is $3.17/gal for regular and $3.33/gal for premium at my local Chevron.

Say the RDX gives you just 1.5mpg more using premium. Let's say an average of 17mpg using regular and an average of 18.5mpg using Premium.*

a distance of 300 miles (roughly one tank of gas) will cost:

using regular gas .... 300/17 = 17.64gallons*$3.17/gal = $55.94

using premium gas ..... 300/18.5 = 16.21gallons*$3.33/gal = $53.98

so you can see that you're actually saving about $2 on a tank using premium, and it simply does not make sense to use regular gas. It's plain stupidity.

* I did a test on my loaner Lexus RX 330, for which premium is recommended, but "regular can be used with reduced performance". I measured a difference of 1.8mpg less using regular gas

So, bottom line, use Premium and learn to live with the pathetic gas mileage!!

FYI...the current MDX using technology from 2000, that is SIGNIFICANTLY HEAVIER (600lbs) and LESS AERODYNAMIC than the RDX, and uses a SIGNIFICANTLY LARGER DISPLACEMENT 3.5 LITER V6 that they were so against using in the RDX, gives the same highway mileage of 23mpg ....now how pathetic is that?? .....every single place I see, Honda keeps harping on the fact that they've used this turbo 4 as a super intelligent way to get V6 power and 4 cylinder fuel economy. I simply can't understand for the life of me, how they can say this with a straight face???....even a half brained fool will be able to see thru this

 

i think they're comparing the turbo 4 with a v6 turbo perhaps. I do agree the gas mileage is shitty for a 4 cylinder engine. Atleast it's not worse than all the v6's out there. I can't wait till this car hits the market in less than a month

 

Help me out here. I thought the need for premium is driven by a higher compression ratio - higher octane to help prevent pre-ignition at a higher compression ratio. But RDX's compression ratio is only 8.8:1. My Accord has a compression ratio of 9.4:1 and takes regular. What is driving the need for premium for the RDX? Is it the turbo or is it just to achieve better performance?

 

It's the turbo. Turbocharged engines, due to the way they are set up, are far more succeptible to premature detonation. The easiest way to limit this is to utilize higher octane fuels. If you look at the recommendation for any manufactuer producing turbocharged engines, the recommendation is the same. Using regular fuel in turbocharged engines generally results in a very aggressive retarding in the ignition timing which results in a severe reduction of power.

 

Thanks CG

 

The Subaru turbo four must use hi-test or engine damage will occur (per the subaru factory engineer). I'd assume the same for the Acura turbo four.

 

I believe the 8.8:1 compression is for 1 atmosphere of pressure in the intake (i.e. when the engine is running off boost). The turbo charger will force more air volume through the intake and into the cylinder, effectively raising the compression in the cylinder beyond 8.8:1. This also increases the risk of pre-detonation, and in general puts more stress on engine parts.

Acura says that the engine block has been reinforced, the connecting rods and crankshaft are forged, and the pistons have been beefed up, all to handle the increased stress on the engine.

From my experience with the Subaru WRX, you might be able to run regular fuel for a while (i.e. an emergency fill up if no premium is available), but you won't save money. The ECU will back off the timing so bad that you'll need to hit the gas more to get moving, and you'll lose a couple MPG as well. Worst case, you start to get some pre-detonation during hard acceleration. I wouldn't risk the long term effects on the engine by doing this repeatedly.

The potential upside will be in aftermarket tuning. I wouldn't be surprised if a reasonably safe tuning for 91 octane gas would yield 15% improvements in HP and torque. I'd like to see more of how the exhaust system is put together (bends in pipe, number of cats, pipe diameter, etc); maybe some power improvements could be done there as well. In the case of the WRX, my gas mileage improved after tuning, because turbo engines typically run extra rich.

That would be my plan if I pull the trigger on the RDX; drive it around a while to figure out the weak spots and look for the aftermarket tuners and ECU reprogrammers to come out with some nice power packages...that should offset this whole v6 argument! ;-)

I sure hope the RDX transmission is more robust than my WRX's, though....

kb.

 

Wow, I really farked that part up; the compression is still 8.8:1, but the pressure in the cylinder is higher because more air can be shoved in there at the start of the compression stroke.

On an unrelated topic, if anyone gets a chance soon to test drive the RDX, can you try it with the AC cranked up? It's 104 where I'm at and with the AC on my WRX really bogs down at low RPM. I'm really hoping the RDX does better.

kb.

 

But...

The "FIX" is "in".

https://acurazine.com/forums/showthread.php?t=2653

 

With the advent of EFI, Electronic Fuel Injection, super-sensitive (non-resonant) knock/ping sensors, and electronically controlled automatic transmissions, it is no longer possible for commercially available fuel grades (excluding diesel) to cause any damage to an engine, even long term.

Knock/ping NOT due to ignition timing can be compensated for by simply enriching the mixture slightly, or in the alternative, downshifting the transmission.

 

Mazda CX7=Turbocharged engine=2007 Model premium fuel was required, but for '08 Mazda made some engine revisions and it now only requires Regular fuel...

Also, There is a difference between what's REQUIRED and what's RECOMMENDED.
Does Acura REQUIRE or RECOMMEND Regular fuel for the RDX?

vicpai posted within this thread stating how the difference is minimal between regular and premium...that was 2 years ago. These days the difference is more like .40 to .60 per gallon AT LEAST, which is significant enough to convince me to use regular.

My wife's BMW X3, we put regular. My GTI, I put premium, because it's REQUIRED for my 2.0T motor. In her car, whether I put regular or premium, she still got he shitty 12-13mpg in the local driving she does. When I drove her car down to FL 6 months ago, I monitored the MPG/total miles per tank every time I filled up. I switched off, with some fillups being regular, and some being premium (making sure all the fuel in the tank is one or the other and not mixed before running my "test". The consumption/fuel mileage with regular and premium was pretty much the same. If there was a difference, it was so insignificant, not worth paying more for premium, when i'm not really benefitting.

Her lease is up at the end of the month, and I'm still trying to decide whether to get the RDX or the Nissan Rogue. HOWEVER if I MUST put premium in the RDX, I may lean more towards the Rogue. I'm strapped these days, and I've heard/seen that the RDX puts down disappointing MPG numbers, which may convince me more to get the Rogue, especially if I HAVE to put Premium in the RDX..She doesn't care what she drives, as long as it's the most cost efficient for us. She says she wants to go back to a Sedan but I won't let her, I need an SUV in my life for the occasional DIY job where I need the space...

[edit] According to Acura's specs on the RDX on their site, it says (but i'm sure you all knew this ) :
Recommended Fuel - Premium unleaded 91 octane*
then it says:
* Gasoline with an octane number lower than 91 may be used, with reduced performance.

Soooo...I think i'll get an RDX....Now I gotta get the wife to check out both of her choices to see which one she likes better...

 

I'm biting my arm as I type this, but considering where you are and the local driving conditions you must encounter to get that awful mpg, a hybrid may be a choice if you can find one at a price that doesn't require 6 years and 200,000 miles of ownership to overcome the cost/benefit ratio.

 

I'm not getting the RDX because of the engine, I'm getting it because it's the right size for our needs...

 

Find it first, talk about it second...

Some of the newer "mild hybrids" by GM have a smaller premium to the model for the technology ($2,000 over the regular version), so it is possible to make it up sooner than you think. HOWEVER, just about every Hybrid on the market today is on some sort of backorder because of the overwhelming demand because of where the price of gas has recently went to...If a dealer has one in stock, expect to pay out of your ass for it. I have a customer currently looking for a Prius. I was told there's a 8 to 12 week waiting list for it now. 3 months ago I they were in stock, and I could buy at at around invoice. I searched and found one of my dealers who I work with had one in stock, they offered it to me for over MSRP. He said "he might" be able to give it to me for MSRP, but he wasn't sure. He said they were fetching anywhere from $500 to $2,000 over MSRP these days....it really sucks...

 

why premium vs regular is an issue? When gas was $3/gal the difference was 20 cents between premium and regular, its still the same now. So back in the day when you purchased RDX it was OK, but now its not, WTF?
yeah, it costs you 2-3$ extra for premium per tank, so what? buy 30K car was not a problem, but now couple extra bucks makes a difference.

 

Not to age myself, but during the last 'crisis' there were places where premium was for selling less than regular. You never know, it could happen again...

If I were in the market today, the RDX would still be on my short list because of the button-push ratio. After all, I traded an Element AND a TL 6-speed for this ride.

Shoofin, admit it, not only is it the right size for your needs, it pushes your buttons. There are other 'right-size' rides that might make better sense, but you just wouldn't feel as good behind the wheel, and that is a big part of ownership experience.

Hell, my girlfriend hates SUVs, but she loves the way the RDX kicks A$$, the quality, comfort, features and is asking me to pick up mulch for her. Take my word for it - your wife will see the light.