2008 and Premium Gas

I often listen to Bill Wattenburg (berg>>LOL) on KGO radio, here in the San Francisco Bay area, 810AM, and I believe that you can get it online kgo.com (the radio, not TV side). Anyway, he is on weekends, at

10PM. He is a well known scientist, nuclear physicist (I believe). Anyway, he has often said that using Premium gasoline is a complete RIP OFF. Unless maybe your car is such a high performance vehicle and will definitely ping badly using regular unleaded. But nearly most of the time is unneeded.

I can vouch for the fact that it isn't true for my motorcycle. Performance on lower octane fuel is noticably worse and running it on the highway with regular is downright dangerous.

bill

A modern showroom-stock vehicle with computer-controlled fuel injection is quite capable of operating on a lower-octane fuel than the manufacturer calls for. The only drawback is that under the highest demand the engine will be detuned enough that the rated horsepower will never be reached. I routinely drive my 2006, which also calls for premium fuel, on "plus" grade around town. And when I know that I'll be burning up the entire tank driving at constant interstate speed on a long cruise-controlled trip regular grade serves just as well -- when I get to the other end I fill up with plus grade again.

I suspect that having tire pressure 2 pounds low will rob the car of more performance than switching down a grade from premium (as well as making it less safe).

John McGaw [Knoxville, TN, USA]

I wonder if this is also true for turbocharged cars like my MSM.

My 1996 BMW 328 conv. requires premium fuel. The engine computer will adjust the engine so that it runs on regular gas. When I tested this, the fuel mileage for a similar trip was reduced somewhat with regular gas. Years ago, a car that required premium meant 49 cents per gallon instead of

29 cents - that was a considerable percentage extra charge. With today's fuel price here, regular is $3.04 and premium is $3.24 - much less of a percentage difference.

At any rate, I figure that my vehicle runs most economically using premium. YMMV.

Jim

Easy to test. Supercharging promotes knock, but if you pussy-foot it, it may be OK. Put in plus or regular, and if the pistons do not melt, you will have saved money. And if you pussy-foot it, you do not have to worry about losing power due to the ECU trying to burn the mixture while it is already in the exhaust.

Leon :)

On regular, the computer will retard the ignition timing significantly, to prevent burning holes in the pistons. The result will be a loss of power, which may not bother you if you're a gentle driver. You'd also have a drop in fuel mileage, no matter how you drive, probably wiping out any cost savings from buying regular instead of premium.

I would only use regular if I needed fuel desperately and premium were not available, and I would only buy enough to limp to the next gas station with a better choice.

Only if the knock sensor detects "pinging", otherwise the timing will remain the same as it would with premium gasoline. Of course, since the engine isn't allowed to ping the driver will probably never know if the timing is retarded or not, so unless you're driving to win an economy championship you'll probably be driving around with retarded timing.

Er, no. A couple of problems here, no loss of power OR fuel mileage if you can drive gently enough to avoid retarding the ignition and, more importantly, are there gentle drivers in Miatas and, if so, WHY? ;-)

Agreed. It makes no sense to not have the power and economy that is available just to save a penny. If you want to run regular get a car that doesn't recommend premium.

FWIW, I used to own a car that absolutely had to have premium but that was when gas was cheaper, I'm glad I don't have it today. That's something I check and if a vehicle recommends premium I'll go look elsewhere, it's not worth it to me.

You can use regular but performance will be lowered and running will become rough. Fuel consumption will rise noticeably unless you pussyfoot around.

My 2005 runs like a hairy goat on regular and with such a tiny amount of fuel used each mile/kilometre, I prefer to use premium and often super premium which gives better consumption figures again.

OzOne of the three twins

I welcome you to Crackerbox Palace.

I'm not sure exactly how the NC's knock sensor functions, but such devices typically retard timing FAR more than necessary at the first ping, and don't recover quickly. It's not an efficient way to control the ignition on a routine basis, it's an emergency safeguard to prevent engine damage. I wonder if it throws an OBDII code?

What octane rating does super premium have? I use 93 octane in my car.

I don't think it does, it's probably considered as normal operation.

The best way would be to try it as the ECU would compensate. In my case in a 2000 with 1600 engine my distance per tank is fairly consistant on a trip and seems to move down from 525k (328 miles) to under

500k (312 miles) with lower octane fuel. Of course this may have changed with the current model and my tests of low octane where on a lot smaller sample.

• J Brockley wrote in rec.autos.makers.mazda.miata:

DAMN! If I tried to get even 312 out of my 2007 PRHT I would be using my AAA membership quite a bit to bring me free gas. I have a 12 gallon tank and on my best runs I get 26 MPG which would bring me to exactly 312 miles.

Well, driving down the interstate at 75 with cruise control on I can detect no difference in mileage which correlates with fuel octane. The outside air temperature, wind conditions, and minor fluctuations in tire pressure seem to have a stronger effect on overall mileage. I routinely record (and I keep meticulous records to satisfy my own curiosity) mileage in the 32-34mpg range under the given conditions and have seen verifiable numbers at and above 36. This is, of course, a limited data set (just under 100 samples) I'm working with and my mean mileage has settled down to 26.8 with a low just above 20. Most of the time I drive around town with plus grade fuel unless I am absolutely sure that I'm going to be on a purely "fun" drive when I'll put in premium or that I'm going to be slogging down the interstate when I'll put regular if I'm thinking that far ahead. Overall I'd say that I am definitely not a gentle driver and am not prone to pussyfoot anywhere -- the number of sets of tires I've gone through in my two Miatas would tend to back up that assertion.

My manual says that my 2000 MX5 has nearly a 13 gal tank (12.8). And on highway trips, the last getting around 32 gal/mi, I usually look to get nearly 390 MPG, near empty. I never let it get that low, but I start planning on a gas stop getting close to that. Maybe I am just great on the gas pedal :-).

My '91 turbo is the most gas pedal/mileage variable car I have ever owned. It gets better than my near-stock '96M did on the highway at cruise, over 30 mpg, and about the same when going easy on it in town.

A heavy foot on the pedal, however, will make it drink an amazingly large amount of gas through those big RC fuel injectors.

Pat

Wow! I realize you're hauling less weight around with a nearly-empty tank, but a twelve-fold increase in mileage is truly impressive.

Sorry, I had to jump on this before Leon could. :-)