i have a 2001 s type v8 and im wondering if by running mid grade or even low i will cause more damage then what i would save on gas.

 

Short answer....yes. Long answer....yes

 

lol okay

 

This was discussed at pretty great length back in June? but I don't think it's a part of the thread title. Try searching for that one.

 

Short answer ..... no Long answer......no

The only time the engine 'needs' high octane fuel is in the presence of pre-ignition/detonation/pinging. This occurs most often under conditions of high load/low RPM. If the engine senses pre-ignition/detonation/pinging, the ignition timing advance is temporarily reduced and no mechanical harm is done. Under these temporary conditions, fuel consumption is marginally increased and engine output (power) is likewise reduced. A conservative driver would probably never notice any difference.

There is a myth that lower octane gas also contains insufficient amounts of other additives needed for injector cleaning etc, but there is no hard evidence I've seen to back that up.

 

Lower octane fuel has no other effects?
Such as leaner running?
Or hotter in-cylinder?
And the jag PCM maps will cater for an octane BELOW their stated minimum?

If there are NO issues, why do jag state a minimum?

 

Octane ratings have nothing to do with leaner/richer hotter/cooler running, or the other myth that it burns faster/slower.

If you have data that indicates that the Jag PCM cannot retard the timing sufficiently to cope, please post it.

 

Why would you want to run a lower octane fuel? Sure the PCM can adjust for it, but just because you can, does that make it the correct thing to do? It amazes me where people try to cut corners to save a buck.

 

I'd run 91 or better octane as a means to run as much ignition advance as possible, resulting in more power to move the mass= less consumption.

 

We all have jag's stated minimum octane. Why do they state a minimum if it's OK to ignore it?

 

Like I said in the post back in June the 3 or 4 bucks you save on the fill up it gonna go right back in the tank when you MPG's suffer and you are filling up more often cause your ECU is reconfiguring for the lower octane and in all actualality you are getting worse MPG. Tested this in my Audi A8 I used to have and running 89 got me worse MPG's then running 92. I cant remember what it came out to be but it really wasnt worth the savings of running 89 octane (dropped that 3 or 4 bucks to maybe a dollar) especially when you look at the power loss.

 

OK, I thought the answer was obvious, but the recommended octane is required to achieve the rated power and fuel consumption figures under all conditions.

As stated earlier, if a driver is not heavy with the right foot, it would probably make no real world difference to either power level availability or fuel consumption.

 

From the handbook:
Use only Premium unleaded gasoline with a minimum anti-knock index (AKI) of 91. Using unleaded fuel with a lower AKI than recommended can cause persistent, heavy `spark knock' (a metallic rapping noise). If severe, this can lead to engine damage. If a heavy `spark knock' is detected even when using fuel of the recommended octane rating, or if you hear steady `spark knock' while holding a steady speed on level roads consult a Jaguar Retailer to have the problem corrected. Failure to do so is misuse of the vehicle, for which Jaguar Cars Limited, is not responsible. However, occasional light `spark knock' for a short time while accelerating or driving up hill, may occur.

That doesn't appear to me to be consistent with using lower octane but depends on how you interpret it, whether you think/hope the PCM adapts OK, etc, I suppose.

 

The octane rating is essentially the rating for the fuel's volatility. A lower octane fuel is less stable than a higher octane fuel.

Jaguar's recommendation that premium fuel be used is to prevent pre-ignition and detonation. Pre-ignition occurs when fuel in the cylinder starts burning prior to the spark due to high heat, which is often attributable to a carbon deposit that is retaining more heat or a number of other "hot spots" in the combustion chamber. A lower octane fuel is more susceptible to pre-ignition because it is more volatile than a higher octane fuel. Pre-ignition results in two separate flame fronts running into each other, one from the spark, and one from the unintended ignition source. When the two fronts collide, it's with great force and the result is an audible explosion we may be referred to as a "ping."

Under the right circumstances, pre-ignition can advance into detonation which is a severe knock that is much more damaging than lighter pre-ignition. Detonation is a very uncontrolled explosion and it can be very destructive to your engine components.

http://en.wikipedia.org/wiki/Octane_rating

A richer fuel mixture (which will help cool the air/fuel mixture), and a less advanced spark will help mitigate the intensity of the two flame fronts that occur during pre-ignition. A "richer" fuel mixture is the key there. If using a lower octane fuel results in your engine pinging or knocking, the anti-knock sensors in the engine will richen the fuel mixture and reduce timing. The richer fuel mixture will cost you fuel economy. The later timing will result in lower cylinder pressure and a corresponding reduction of torque at all rpms (which will reduce your horsepower).

If your engine doesn't sense any pre-ignition, you won't see the hit in power or fuel economy, but Jaguar set their rating because they're assuming you will need the extra octane rating.

 

That tells me that the PCM will adjust for "knock" to a certain extent as long as you are using at least the minimum 91 Octane rated fuel. Anything lower and "all bets are off" and "if you break it, it's on you cheapo"..

That's how I interpret it.... So, yes, they call for it, run premium. It's 20 cents a gallon more here. That is exactly $3 more per 15 gallon fill.. Hmmm at current prices... $43.35 vs $46.35.... Easy choice..

 

didnt mean to cause an argument but here it can be anywhere from 20 to 40 cents off and i was just wondering what the actual effects would be, like im not going to destroy the engine if i try mid grade right? and if i dont hear any pings its not causing any damage? or is their build up or something like that. Im just at a loss because i drive 10.2 miles to school and 10.2 miles home and its costing 50 or 60 for gas a week (i think need to check receipt)

 

You're not driving enough to get the engine properly warm, I'd think

 

...Hey don't feel bad, the question you asked is important, because for those of us who drive the Supercharged Jags, gas can be really expensive. So what if we use the mid grade, and every week throw in a STP to clean out the injectors? I don't see how this can harm the engine in anyway if you use the mid grade gas and use once a week STP

 

It would appear that this topic has an orbital period of 5 months ...

Why not pick up the old thread and everyone can simply post:

"What I said before" ...

 

I don't even look at gas prices. Do the math- how much do you really save by going down a fuel grade? Honestly. ~$5 maybe?

Every little bit of money saved adds up, but using cheaper petrol just isn't worth it to me.

If you wanna play, you gotta pay.