Run it on regular?

January 30, 2007 4:59 AM

I am looking at purchasing a 99 Land Rover Discovery and I notice that it runs only on premium gas. Is this absolutely necessary? Does anyone with experience with a Discovery have any opinions of this vehicle? I heard that the diesel version is a better choice. Thanks in advance.
posted by scooters.toad to travel & transportation (23 comments total)

You don't list a location in your profile, but if you are in the US, I'm pretty sure that the diesel version was never imported. You could certainly do an engine swap, but that is a lot of work and money to avoid premium gas. (There may be a number of grey-market imports in the US with diesel engines, so that may be an option as well.)

(Also, the reputation for terrible reliability would worry me a lot more than the question of premium gas, but the vehicle certainly does have its fans.)
posted by Forktine at 5:11 AM on January 30, 2007

I owned a brand new 99 Land Rover Discovery - always ran it on premium so I don't know about running it on regular.

That vehicle was in the shop more often than it needed oil changes. It was all under warranty, the dealer was close by, also I was always given a free loaner.

I would never buy one again, especially that year/model.
posted by thilmony at 5:14 AM on January 30, 2007

There was an article I read recently about types of gas in the US and what they actually mean (I was quite skeptical before this). The octane levels in the gas (which create the ratings like 87, 93, etc) actually do make a difference depending on what your engine is tuned to use. Some vehicles should *only* take higher octane levels (premium), some should *only* take lower levels (economy), and interchanging octane levels with engines can create engine knock problems. Not catastrophic, but not great for your engine either. So if it says to run premium -- and there seem to be less than fantastic reviews for reliability in any case -- I'd listen to it and give your engine the gas it wants to get as much life as possible :)

Disclaimer: IANAMechanic.
posted by olinerd at 5:43 AM on January 30, 2007

Your premium gas is the UK's regular gas. We don't even have the low-octane stuff you guys sell. The engine is a UK-designed, so I imagine it really does need at least 95 RON.
posted by bonaldi at 5:43 AM on January 30, 2007

Thank you all for the feedback. I am located in the US and although I really like many aspects of this vehicle the more reviews that I read the more that I am leaning away from purchasing it.

Once again, thank you for your inputs and have a fine day.
posted by scooters.toad at 5:48 AM on January 30, 2007

Recently, as one of their "Everything You Need to Know About Everything" articles, Esquire magazine ran a sidebar in an article about cars that said you're basically a sucker for buying anything but regular unleaded so long as you're not hearing your engine pinging. I'll see if I can find that issue, but perhaps someone else has it lying around next to their computer?

I do remember thinking I'd been a chump for buying premium gas for the last few years, particularly with the cost of gas.
posted by mrkinla at 5:51 AM on January 30, 2007

Yes, it eats premium, and yes, it's likely to be broken a lot.
Google Lucas Electronics jokes for all the gory details.

We have one. It's a money pit.
posted by unrepentanthippie at 5:52 AM on January 30, 2007

Most modern electronically-controlled engines, in the presence of knock, will advance spark timing to reduce said knock. They will, obviously, need to do this more when you're using less knock-resistant (read: lower octane) gas. This is not necessarily bad for the engine; however, you won't get as much power out of the engine if the timing is always advanced.

On older, non-computer-controlled engines, this can be a serious problem (lessons well learned), but on a newer vehicle, it's just a performance issue.
posted by notsnot at 6:12 AM on January 30, 2007

My wife drives exactly this car. I was opposed to buying it because of the reputation for unreliability. She really wanted it because it was cute. So we compromised as married couples do and bought the car.

Much to my surprise, it has been extremely reliable. We have done no major repairs in 4 years--though when it does need something the parts are expensive. And it is really fun to drive, you feel the road in a way you do not in an American SUV. I still think we just got lucky, however. And yes, it sucks down the premium.
posted by LarryC at 6:21 AM on January 30, 2007

Recently, as one of their "Everything You Need to Know About Everything" articles, Esquire magazine ran a sidebar in an article about cars that said you're basically a sucker for buying anything but regular unleaded so long as you're not hearing your engine pinging. I'll see if I can find that issue, but perhaps someone else has it lying around next to their computer?

Well, that article is completely wrong. Use the octane level recommended by your manufacturer. A modern car will not ping or knock at lower octane levels, because the car's ECU can compensate for lower octane levels by retarding timing. This will sacrifice performance, perhaps reduce fuel economy, and perhaps cause premature carbon build-up in the engine.

Many new cars are using high compression engines to extract as much HP as possible from an engine of a given size. These cars will typically recommend 91 (R+M/2) octane fuel, and it's for a reason. Octane is a measurement of the tendency of gasoline to combust under pressure. The higher the octane rating, the more compression the gas can withstand before combusting. In a high compression motor, or a motor with a turbocharger or supercharger, the air/fuel mixture is under tremendous pressure.

There is no conspiracy here, the octane level recommended by the manufacturer is almost always what you want to be running. (Consequently, if the recommendation is 87, then buying 93 is a waste of money.) (I'm using US octane ratings in this post, apologies to European and Asian readers.)
posted by knave at 6:32 AM on January 30, 2007

Your premium gas is the UK's regular gas. We don't even have the low-octane stuff you guys sell. The engine is a UK-designed, so I imagine it really does need at least 95 RON.

It's like US vs UK gallons --- the word is the same, but we measure them differently. From the Wikipedia page on octane rating:

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-95 (regular) in Europe.
posted by Forktine at 6:50 AM on January 30, 2007

Actually, retarding spark advance reduces knock - advancing it makes it worse. Also, typically engines will be more prone to knock in hot, dry weather. I also agree with following the manufacturer's recomendation. Normal knock control has calibrated limits that might not cover running 87 octane in a "premium only" car. This is different than a "premium recommended" car, which can probably handle normal unleaded OK - it has different compensation software.
posted by rfs at 6:53 AM on January 30, 2007

Forgot to add:

The engine is a UK-designed,

But based on a 1961 Buick engine. Whether that means "tried and tested," or "old and outdated," I don't know.
posted by Forktine at 6:53 AM on January 30, 2007

Except in the case of a "lemon", it's not that unreliable. Even the least realiable of modern cars (which unfortunately comprises the Disco) will start 99% of mornings. That being said, if trouble-free motoring is a high priority for you, then get a Japanese car.

Most people I know with Discos of that era (I travel in Land Rover circles...) have not had any major problems. From time to time I read the horror stories.
posted by Harald74 at 7:17 AM on January 30, 2007

Forktine: But based on a 1961 Buick engine. Whether that means "tried and tested," or "old and outdated," I don't know.

It means both... Still more than drivable, though.
posted by Harald74 at 7:20 AM on January 30, 2007

Actually, retarding spark advance reduces knock - advancing it makes it worse

this isn't right. (unless you are implying some kind of double negative by the expression 'retarding spark advance').

knocking happens when part of the air-fuel mixture ignites before the combustion front coming from the spark plug gets there. engine computers compensate for knocking by making the spark come earlier in time, so that you get the proper ignition dynamics. it doesn't make any kind of sense to make the spark later in the stroke, as the preignition will just be worse.
posted by sergeant sandwich at 8:32 AM on January 30, 2007

Correct me if I'm wrong, sarge, but my understanding is the knock response loop will retard ignition timing, because this will produce cooler cylinder temperatures, eventually reducing the detonation situation.

Example:

As soon as any aut of range signal is sensed, the ECU will retard timing by an amount determined by the intensity of the input. If that corrects the condition, the ECU will then advance the timing again, until knock is heard, the back it off again. This process continues until the maximum advance possible without detectable detonation is achieved.

posted by knave at 8:52 AM on January 30, 2007

My mother's Tundra requires premium. I drove it once when she'd gone cheap and put some regular unleaded in there. I could hear pinging at anything more than grandma acceeration.

Yes, the ECU in the car will dial back the spark advance when it senses knock. However, it has to hear the knock in the first place to detect it, and it only takes one detonating cycle to blow something. If the engine were under heavy load, it is conceivable that damage could occur before the ECU had time to react.

Sergeant, you've got it backwards. Premium has the potential to make more power because it burns slower, allowing the ignition to advance the timing - that is, spark further in degrees before Top Dead Center - which gives the expanding gases more time to act on the piston. So, when knock is sensed, the timing is retarded, meaning reducing the number of degrees before TDC that the ignition event takes place.
posted by kableh at 9:13 AM on January 30, 2007

hunh, i'll be damned. i always had it backwards. it's a little bit unintuitive, but the cooler cylinder explanation makes sense, knave.. thanks.
posted by sergeant sandwich at 12:34 PM on January 30, 2007

Point of reference: my 03 Jetta with the 1.8T engine says it wants premium gas. It runs just fine without premium, however I get an additional 4 miles to the gallon when I use premium (and I get noticeably more punch when enjoying my pseudo-sporty sedan). With a 20 cent difference between premium and regular, it is a worthwhile cost just for the fuel economy.

Now if someone could explain to me why I can't find 93 octane (which was readily available in Wisconsin), let alone 95 in this fine state of California.
posted by fief at 4:00 PM on January 30, 2007

why I can't find 93 octane

In California we have a reformulated fuel which also affects gas mileage. Yes--it sucks. Try Union 76 if you really need it. Some of their locations carry race fuel which you can mix into a regular tank if you truly need it.

I also have a Toyota Tundra. Premium fuel is recommended. So it gets 87 octane. It's a truck for fucks sake. My Acura TL requires premium, and after driving a rental on cheap gas, and noticing a huge difference, my own TL will never see 87.
posted by vaportrail at 4:42 PM on January 30, 2007

A followup on high octane gas in San Jose, CA. Some 76 stations carry 100 octane gas. It appears to be the ones that do NOT have diesel yet have two dispensers on one of the pumps. I can confirm myself that the 76 station at the corner of Almaden and Foxworthy has it.
posted by fief at 11:42 AM on February 1, 2007

Now if someone could explain to me why I can't find 93 octane (which was readily available in Wisconsin), let alone 95 in this fine state of California.

People talking about 95 are almost certainly talking about the RON octane measurement. In the US, we use the average of the RON and MON measurements, which will generally be lower than the RON number. It's an important distinction.

Also, watch out when you find 100 octane gas in the US. It's quite possibly leaded race fuel, that will ruin your catalytic converter.
posted by knave at 1:11 PM on February 1, 2007