Any issues running 98 octane in 4.4 X5?
 

Hi All,

I have usually always used 91 octane petrol in the past, however, I seem to have got a bad fill and put 98 to give it a boost. After a few fills of 98 the engine response now feels much better but was just wondering if there would be any long term issues constantly running on 98 octane. Does it make the engine run hotter? Does the fuel mixture need re-tuning? Any downsides apart from the extra cost at the pump?

I would assume that in Australia you are using the Research Octane Number (RON) to refer to octane rating, similar to Europe. In North America, we use an average of RON and the Motor Octane Number, two different test protocols, and call it the Anti Knock Index (AKI)

In North America, BMW recommends 91 or 92 AKI, I can't remember which. Vehicles require a minimum of 87 AKI, with a possible loss of mileage and performance, and many run fine on 89 AKI with no loss of power or performance. Other vehicles don't run well on anything less than 92, primarily because fuel varies widely in quality across North America.

There is no precise conversion between RON and AKI, but it is about 5-6 points usually. So, 98 RON is the same as the 92 AKI recommendation, and many vehicles will run fine on 95 RON, which is similar to 89 AKI in North America.

If you are using the RON scale, it is not surprising that your vehicle would run better on 98 than 91 (which is similar to 87 AKI). I would use 95 RON in any case, and see if you can tell a difference. If you can't then carry on. If you can, then use 98, unless BMW Australia has a different recommendation.

If you are using the AKI scale, and it runs fine on 91, there is no advantage to providing fuel with more AKI than the engine is designed for, apart from the fact that the tank of fuel you purchased may be fresher, or may have higher concentrations of cleaning agents, both of which would explain improved engine response.

Higher octane fuel than that which the engine is designed for does not run hotter, does not contain more energy, and does not benefit an engine, but it does lighten a wallet. The exception to the above is if you have aftermarket modifications that increase the compression ratio, such as different pistons or forced air induction (turbocharging or supercharging).

Higher octane gas also smells nice and sweet when burning :) I've run high octane in the M5 and TL, and they both loved the stuff. I agree completely w/ what JCL has said. I always run the minimum of what a certain vehicles requires because anything less usually causes pinging, causing the engine to back off the timing and in turn you get reduced HP and mileage. Running more than what's needed (if you know that you don't have pinging issues) is usually just a waste of money. I run anything from 91-93 (preferebly ethanol-free) in the BMW's and bike, but I run 85-87 in my truck because its definately not a high compression/HP beast. I have no idea how to convert AKI to RON, but as long as your running the minimum of what BMW put on the label of your gas door, you should be fine. Unless you hear audible pinging (some older cars exhibit it really clearly), putting in the more expensive gas is like buying $$Dinan$$ parts...its a placebo effect that you feel like its faster because you've spent 2x what the average is. :)

So you mean to tell me, my dinan sticker doesn't increase torque?!?! :wow:

ROFL I seem to never be able to find anything thats about 91 or 92 everythign iv seen so far is always 93, and been always going to Hess never caused my engine light to go off unlike Mobile and Shell.. i dunno why but w.e Hess is cheaper and closer

I am using 95 since I bought the car ... 3.5 years now with no problems!

Most likely 95 RON, which is what we call midgrade, or 89 AKI, in North America.

I spoke to an owner of a fuel station and he said that while most of the time fuel all comes from the same places that each seller adds their own additives and that higher compression vehicle will actually react differently.

I don't know about X5's, but I've seen some 740's that had a label asking for 89 and others asking for 91. I'd bet that if Essam's X5 asks for 91 AKI that it'd run even better, especially in the kind of summer heat he gets in his area.

That is true on the distribution side, ie from the production facility up to the filling station. On the retail side, the variables are freshness of the fuel, tank sediment, water in the fuel, and whether the retailer is actually selling what the label on the pump says (whether intentionally, which is fraud, or unintentionally, which is incompetence)

Essam's stations in Saudi Arabia will be providing fuel measured in RON (usually only North America is stuck with AKI). Unless he has a grey market import vehicle (ie US spec), BMW will have specified a fuel in RON.

Since it's the same motor, why would they have different fuel requirements...besides emissions differences? I would think that if it requires a higher octane (91+ at least) it would be required every since these motors run so hot.

My car is Arabian Gulf Specs which is Euro specs plus some extras to operate in extreme hot weather ... tomorrow I will go check the fuel door and see what's written in there

Do you know what the extra hot weather items are? I'd like to add them just for my own precaution.

I don't know the items in specific but we always have a badge saying that the car complies with GCC (Gulf Countries Counsil) specs.. Cars imported from Europe or USA directly, not through the dealer are usually having a lot of heating problems and their AC is not efficient.

They don't have different fuel requirements, they have a different way of identifying the same fuel.

I figured that, that's why I was wondering what Essam's sticker says and I brought up what I've seen in various 7's. If all X5's requirements are the same, then he's been putting in the wrong grade.

I only put 95 RON in mine. I've used 98 RON before, but find that while the car seems to have a little more power (maybe it's just my mind justifying the higher price) the car certainly doesn't run as smoothly. I had the same experience with both of my MINI Cooper s's prior to the X5 and our 3 Series. All run rough on idle. Our local dealer recommends using 95.

Here is the tank door .. saying RON 91-98

.

That's quite a spread. What is that converted to AKI?

In round figures, 87 to 92, roughly the same as North America. There is no direct conversion, as the Motor Method and Research method are different test protocols (a test engine at high rpm vs a test engine at low speed). The vehicle is designed to run safely on 87 AKI, but better fuels are recommended.

Considering the heat in his area, along w/ the fact the BMW decided to Essam's car w/ extra climate control measure, I'd run nothing but 98 RON just to prevent knocking in that kind of heat as little as possible.

As for John, his climates aren't any different than what I got in Seattle, so I'd stay in the middle of the 91-98 RON if it was me.

I know there are conflicting opinions about using higher vs lower octane, but using the cheap or too low of an octane in BMW's has never served me well. This is my .02, but using the highest recommended octane will net better gas mileage as opposed to using lower octane in an effort to save money because you will get worse gas mileage, making the cheaper stuff a wash anyways.

Australian spec 4.4s are designed to run on 98RON. You can also use 95RON while the minimum permissible grade is 91RON. Personally I wouldn't use anything below 95RON except in an emergency.

:iagree:

So maybe it breaksdown like this:

91 RON = 87 AKI
95 RON = 89 AKI
98 RON = 91 AKI

Sometimes I can find 93 AKI, which might make into like 101-102 RON, which I prefer whenever I can find it.

My understanding is that AKI = RON minus five, or thereabouts.

It isn't a linear conversion. Two different fuels can behave differently on the two different test protocols in the test engine, and so may have the same RON but different MON results, resulting in different AKI figures. As mentioned in post #7, 89 AKI = 95 RON for all intents and purposes, about 6 points. 91 RON is close to 87 AKI, about 4 points. 98 RON is about 91 AKI, about 7 points.

I filled up with 94 AKI at Chevron today, mainly because the idle was a little uneven after a lot of short trips in the city, and I wanted a tank with the maximum amount of Tecron in it.

That is a blanket statement, and not entirely correct. The best fuel for any vehicle is the lowest AKI rating that doesn't cause the engine management system to adjust the timing to prevent knock. That may be the same as the recommended fuel, but it is unlikely. Fuel quality and specifications in the real world follow a bell curve, so the manufacturers specify a fuel that will nearly always be OK to use. That puts the specified fuel above the average required AKI, if you believe in bell curve distributions.

It has nothing to do with saving money, to me, since the savings are only pennies. It has to do with using the best fuel for the engine, and that isn't necessarily the highest AKI, although it sometimes is.

The safest and easiest is still to use what the manufacturer recommends, but using a lower AKI won't reduce power or mileage until you get low enough that the timing is retarded by the engine management system. That is why my vehicles always ran on 89 AKI (until I got the 535i with the turbos), as it was better performing in winter (we don't get high temperatures here). 89 solves some hard start problems over 91 AKI, in cold temperatures. Best mileage I ever got in the X5 (and the Z4) was on 89. However, we have high quality fuel here, and you may need to get to a pump label of 91 to get the same real world AKI, depending on where you are purchasing it in North America.

I know; due to the different methods to obtain RON and MON. I only suggested the -5 conversion from RON to AKI as a quick guide.

In Saudi there is only 91 and 95 RON
In Egypt my home country we have 80 :D , 90, 92 and 95

80?! Is that a special lawnmower mix ;)

run 98 4.4 v8 it gets 15 ltr to the 100kms used 91 the first few weeks we had it and got 19-20 ltr to the 100kms
But yes Aus fuel quality is very poor really , only use high turn over stations that don't have tanks half full of water .
I drive 5kms past my closest servo because the X just doesn't like that flavour of 98 always runs rough ,go up the road and use their 98 and smooth as new

Love your quote prgsxr.

cheers mate , world would be a much safer place and the stupid thing is if you removed all warnings you eventually wouldn't need them anyway because only people with common sense would still be alive.

We can all dream, ehh.

I think it's funny that a friend of mine Ferrari F40 doesn't have a single yellow warning sticker, yet even the most base model Ford Focus will have them litered throught out. Dumb Americans who will sue anyone for anything if they can't accept their own responsibilities.

Oh well, moving on... ;)