Really, What would Happen???

[Ross_Thoma]

What would happen if I switched to regular 89 or 87 octain in my 03?

Is the milage that much better, if there is any difference at all?

Shoudn't the computers and knock sensors and other gizmoes retard or advance spark or make other changes as necessary, If not why are they built into the engine. I guess that if things get a bit hot you can get detonation (???) but here in michigan it ain't that hot and the damn things liquid cooled anyway, maby I coud get a cooler thermostat?

Maby I am dumb but am I missing something??? They say to use permium but only tell you it will void the warrentee , other than testing the remaining gas in the tank how can they tell? If there is an octain sensor for them to record the infraction why not tie it into the computer and get another data point for the eng. man. system

Just thought I would toss it out there.

Please enlighten me, thanks

Ross Thoma

 

[Andrew Homan]

They can't tell. I use the cheap stuff in mine. granted its an old 95. I use injector cleaner more to prevent carbon build up but thats it. Your choice. try a tank or two of the cheap stuff. not that any of its cheap now

 

[Creemore]

Maybe nothing, maybe something.

I don't know about this engine in particular, but generally speaking, if a manufacturer specifies premium in a knock sensor equipped vehicle, it needs it (what would they have to gain by making you spend more on gas?). If that engine gets fuel with a lower than specified octane rating and the engine detects incipient knock, it will retard the timing slightly and enrich the mixture to prevent it. The result is USUALLY worse mileage, not better, and a significantly reduced service life for your catalytic converter (not to mention in some cases less power).

I'm really interested to hear what experienced LR owners have to say, but I'll be hoping for consensus or else take it all with a large grain of salt. I've seen hair pulling debates about this on a BMW board I visit, and that's a car where the consequences of running regular are simply inarguable based on published data. It's a strangely emotional issue for people.

Me, I pay the extra 11 cents a litre for premium in my Disco because LR wants me to. I get 20 miles per imperial gallon in the summer, and 16 or 17 in the winter. It's cheap insurance, and a pitance compared to what you can spend on these things if you don't take care of them. Flame suit on...

 

[Randy]

This is an excerpt from my Motorcycle forum on octane, detonation, etc.:

"Many people have reported either audible detonation or "pepper" spots on the spark plugs when attempting to run regular or mid-grade gas. The pepper spots are carbon deposits in the engine that have been dislodged by the violence of the explosion created by autoignition.

From the April 1995 edition of Muscle Mustangs and Fast Fords (p.40):

'. . . the worst kind of detonation is the kind you can't even hear. . .

In automotive terms, detonation is uncontrolled combustion. Under normal conditions, the burning of the air/fuel mixture is controlled by the ignition timing and compression ratio. Under ideal conditions, the cylinder pressure would be peaking just as the piston reaches top dead center. At this point, the mixture is fired and the exploding gas forces the piston down. It's when the pressure peaks when the piston is still coming up that detonation begins. In this case, when the timing is too far advanced, the spark is firing far before TDC and the exploded gas tries to resist the upward motion of the piston. Instead of waiting for it to cross TDC and force it down the bore, it's trying to force it back before it even reaches TDC. Because the piston is fighting the explosion, cylinder pressure escalates catastrophically.'​

My advice: Run premium. If you want to play... "​

 

[Jake]

Good arguments all, when considering a higher compression engine, or advanced cam timing. Rover V-8 has neither. so I don't understand the requirements.

 

[jmoore]

Sure you can use a lower octane, the engine can handle it, but I wouldn't for very long.

When you use a lower octane, the ECU retarts the timing to compensate for poor detonation. The burn isn't as clean and you get carbon build up on the valves.

Ever wonder why some many older Rovers need a valve job? Pay now or pay later.

 

[Jake]

I burned regular for over 145 thousand miles in my 94, which eventually accumulated 345 thousand miles. There seemed to be no difference in performance or mileage. The engine never had valve problems or a valve job and was running when the truck was totaled.

 

[Randy]

Forgive me if I have this wrong, but I don't think the '94 had a requirement for premium? We have a '95 RRC LWB with the 4.2 and it runs on regular and has no premium fuel requirement.

 

[geoff]

The pistons are aluminum. Regular burns hotter, and detonation can burn a whole in the piston. I think on www.pirate4x4.com someone had pics. Typically this would happen pulling a trailer or otherwise using the full potential of the engine in hot, dry conditions, and is pretty rare.

My rule of thumb, premium is required mainly in summer when the humidity is low and/or you are pulling something. In the winter, when the car runs in warm up often and intake temps are cold, regular is fine.

On the newer cars, the computer might log when it shifts the timing to a new (retarded) map. Not sure.

You should get slight better mileage with premium, although it won't be obvious on every fill up.

 

[Jake]

From what I recall, the 94 owner's manual required premium fuel for the engine. There was also a sticker at the filler neck.

 

[cyoc62]

They're like women; once you start spending more on them they begin to expect it more often. When you return to the cheap stuff, their performance suffers. Or so it seems.

 

[macklow]

I've been using regular unleaded, anywhere from 87 to 85 octane depending on how high in the mountains I'm buying fuel. I have a '95; the owner's manual states that I should use premium unleaded. My '95 doesn't have any fancy electronic ignition, just the old-fashioned distributor.

I have over 200,000 miles on the the engine with no work ever done on it... it has the original valve cover gaskets. On the other hand, I get bad driveline vibrations with the MD OME springs!

 

[Randy]

I stand corrected. Must be just the 4.2 then, but that surprises me. Regardless, it runs great on regular.

 

[Andrew Homan]

Me, I pay the extra 11 cents a litre for premium in my Disco because LR wants me to. I get 20 miles per imperial gallon in the summer, and 16 or 17 in the winter. It's cheap insurance, and a pitance compared to what you can spend on these things if you don't take care of them. Flame suit on...[/QUOTE]


Man you are my new hero. I'm happy with 15-16 hwy and 10 in town.

 

[Creemore]

Good arguments all, when considering a higher compression engine, or advanced cam timing. Rover V-8 has neither. so I don't understand the requirements.

What you say is true, but there are other reasons besides high compression for wanting to use premium fuel. Remember that this motor was originally designed in the era of leaded fuel... lead was there to prevent 'knock'. Between having to adapt it to modern fuel, having to squeeze a few more ponies out of it to be competitive, and meet modern emissions requirements, I have the sense that they've pushed things like timing and air/fuel mixture to the limit, but I'm no expert on this. Anyhow, at 9.38:1, the engine in my Disco 2 actually is high compression by mid-1960s standards...

 

[syoung]

Lead was there to prevent predetonation? hmm... I thought it was there for the valves.

 

[Creemore]

Lead was there to prevent predetonation? hmm... I thought it was there for the valves.

"Leaded gasoline was discovered on Dec. 9, 1921, at the General Motors research labs in Dayton Ohio. GM researchers had been testing fuel blends since 1916, trying to stop engine "knock." Knock was a problem that was preventing the development of higher efficiency, higher compression engines. The problem was early, non-uniform detonation of fuels in the engine cylinder."

Lots on Google. This was from http://www.radford.edu/~wkovarik/ethylwar/overview.html. I'm sure there's other, better info, but I wanted to make sure I hadn't had a brain fart...

 

[justinhaaga]

I thought lead was added to increase octane? Which with technology increases we have better ways to due it that does not pollute as much.... Anyway, on this subject - if the engineers recommend premium then premium is what I will run. They should know more than anyone, what do they have to gain?

 

[p m]

I thought lead was added to increase octane? Which with technology increases we have better ways to due it that does not pollute as much.... Anyway, on this subject - if the engineers recommend premium then premium is what I will run. They should know more than anyone, what do they have to gain?

yes, tetraethyl of lead was used to increase octane number of the gasoline. The same could be achieved by better refining process - which was eventually mandated in the U.S. to stop lead pollution.
What do engineers have to gain? Maybe nothing. But, using 92+ octane gasoline may be the only way to achieve the horsepower number they advertised. In any engine where there's a knock sensor, the engine computer will retard timing once it detects detonation - it will eliminate detonation, but at the cost of power loss. My WAG for power loss would be about 3-5% running 85-octane fuel.

 

[Creemore]

I thought lead was added to increase octane? Which with technology increases we have better ways to due it that does not pollute as much.... Anyway, on this subject - if the engineers recommend premium then premium is what I will run. They should know more than anyone, what do they have to gain?

We're agreeing. Octane isn't a substance, it's the measurement for a property of fuel.