Car Talk and premium gas

Modern ECUs can tell what kind of gas you have been running by the amount of retard on the timing combined with the number of times the knock sensor activated. If the timing hits base and the knock sensor still fires, the fuel grade was too low. Guess what? No warranty from any resulting engine damage even if had nothing to do with the fuel.

Here in Oz, current unleaded fuel grades are 91, 95 & 97 RON, with or w/o ethanol. *Everything* post 88 is required to accept 91RON *but* a significant (and increasing) number of cars specify minimum 95 or 97 and

*will* show decreased performance &/or economy with the base grade.

My 99OB is recommended for 91. Ditto 02 2.4 Camry and an 83 carburettor Nissan my daughter owns. On these and many others higher grades make NO difference except higher cost. OOTH, pre EFI cars can suffer catastrophic damage from pinging/detonation over not too great a time.

My 81 Saab turbo requires min 97RON, copes with 95 ethanol, sulks a bit on straight 95 and runs like rubbish on 91 on all but eggshell throttle openings! By contrast, 85+ APC Saabs will run ok on everything from kero upwards - min 86RON IIRC.

Anything post unleaded will run on base grade, but if it specs premium, then there *will* be a performance tradeoff running a lower grade. If you just noddy around it may not show up. If you back off when it starts pinging its head off you won't do any damage, *but* it's all a bit like the old so called "motorbike mechanic's torque wrench" method - tighten it 'til it strips then back it off half a turn! If you're running through hills with a full load plus the air and sound on, I doubt if you'd know it

*was* pinging until something broke!

Maybe better to just pay the money or select a different car in the first place? Cheers

That may be true in Oz, but not neccesarily in NA. If you do not run the correct grade of fuel here, and there is engine damage (even if not directly related) they won't honour the warranty. Also, NA-spec cars are different than the rest of the world.

For example, the STi. It recommends 93. The user manual tells you in the absence of 93, you can use 91. However, no lower grade should be used. In many places in NA, 93 is not available. I can tell you from experience that the STi will ping on 91 on warm day, and since I have the car instrumented, I can also tell you that timing reaches base when that happens. It can no longer compensate.

Cite an actual case where a warranty was denied based on fuel use. Should a dealer hedge n warranty repair (none will), Simply claim gas was low and the only nearby gas was regular. If they continue to stall a call to the local troubleshooter/consumer advocate will get the dealer and the car maker negative publicity they do not want. The whole premium requirement is a crock. Again, buy me a new FJ cruiser and I will never use premium. Any warranty issues will be dealt with by Toyota with no problem and the vehicle will last me the average of

8 years I normally keep a vehicle. If youre so c> Modern ECUs can tell what kind of gas you have been running by the amount of

I don't need to. Read the friggin warranty guide for a WRX or an STi.

Secondly, even if you are right (which you're not) you won't save money because the reduction in gas mileage and performance will more than offset the slightly higher cost of premium fuel.

There are a variety of ways in which a car can be 'detuned' to run regular. Cobb AP on economy mode is one. If you install an AP it will void your powertrain warranty; there are TONS or real-world examples of that happening.

Your loss!

I have the same engine in a Tacoma. Premium is recommended, not required, so you really don't have to use it. Warranty coverage will not be an issue as far as 87 octane goes.

Where you'll lose is never getting to enjoy the full potential of the engine, as well as an overall lower cost per mile for fuel. That's right, premium is cheaper!

Yes detuning re-tuning, chips etc may cause a dealer to question whether or not car was abused or raced and they may try to weasel out of a major repair. However , I doubt the WRX STI manuals say clearly in bold letters "The use of less than 93 octane gas WILL result in engine damage and disclaiming of warranty" It likely mentions nothing of damage. I only have the outback manual. I will look and see if there is mention of engine destruction with the 3.0 which asks for premium. I doubt it.

I have the manual "Your car requires the use of premium fuel of 93 octane or better. If 93 octane is unavailable, 91 octane may be used temporarily. Driveability may be affected. Use of lower grades of will result in poor driveability and may result in engine damage."

I don't know how much more clearly it could be stated.

It doesn't matter. It quite clearly mentions the possibility of damage from wrong fuel types; which is what just about everyone has been telling you. The warranty is not mentioned in the Owners Manual at all. It is a separate guide. It is more of what is not covered by both the OEM and the extended warranty. But it does state that if the vehicle is not used or maintained within the parameters recommended by Subaru that the warranty may be voided.

Think about it for a second. The warranty is to cover manufacturer's defects and premature failures, not failures due to misuse or incorrect use. You wouldn't have a leg to stand on.

maintained

Yeah, but if the man wants to buy a new vehicle cos he thinks it's cool then have to drive like a granny so he can scrimp pennies by buying the cheapest fuel around then that's his choice I say! FWIW, if I could afford an STi - and do without the wagon - I think I'd take the fuel requirement as a necessary cost and have a grin on my face anyway, same as with the bike. Cheers

My attitude exactly; well said!!!!

That's how I feel. I didn't buy the thing for economy. I have the daily driver for that.

However, every now and again we get the question as to whether you can burn low-grade gas in a high-performance engine. The answer is, of course, no. But if someone is asking, it means they don't know and so I can't let go when I see someone give those people a bullshit answer that could leave them in a real pickle.

high performance (as it relates to acceleration) is high power to weight ratio. NOT 'V8' . PLENTY of vehicles are high performance with fewer than 8 cylinders.

And, since many people agree with you and would not buy a car that required premium fuel, there is a big incentive for manufacturers to point out the fact that their cars are designed to run on low octane fuel IF THAT'S THE CASE! So, why recommend mid or high octane? because that is what the car is DESIGNED to be operated with.

Do you run straight 20W oil? Don't wanna give the oil companies too much money, remember? ;^) It might be cheaper and your car will likely run for 150k or more miles with it. BUT - with the PROPER oil it may run for

200K or more. Using low octane and getting 'slight' pinging on occasion may be in teh same caetgory of long term, 'slow death'.

Carl

Good for you. If a V8 is your idea of high performance, that's cool. Most of them don't require high octane fuel. Generally, it is high-compression or forced-induction engines that require it. If you would never buy premium, at least you don't buy a car requiring it. Those of us liking small, nimble cars with small but high horsepower engines, get forced-induction or high-compression; which require premium. Its no myth.

Incidently, I always use the fuel for which my car is designed. I generally get 350,000 KM (210,000 miles) out of my cars and I sell them still working fine.

To me 4 cyl are economical and regardless of how quick a car might be there is nothing like the rumble of a v8. Oil costs the same so weight is not a factor in cost. Longevity is a matter of design and maintenance not oil weight or cost. My 86 Dodge daytona got whatever oil was cheapest. Ran over 100k but dodge quality came into play and it was needing ,major work (not engine).

94 Trooper used syn blend and ran to 140+k til hit. 04 outback used full syn since about 7k. Usually walmart super tech - $13 for 5 qts SL rated full syn. I have no doubt I can get high mileage out of subie but will probably trade next year if Wrangler Unlimited is sold in yellow or better colors than available now and to allow kinks to be worked out. If someone wants to put premium in their car thats fine. It just bothers me when some people who are trying to feel an ego boost " my car is high performance" are led to believe "damage will result" which is just not true. Does slight occasional pinging cause damage? Probably not IMO. If I get 8+ years from a vehicle with no major repair bills, I'm happy. After a point I choose to buy a new car rather than put money into an old one but thats my choice. I just cannot in good conscience give those oil companies a cent more than I have to. Iwalk and cycle to handle most errarnds. so I will not buy a higher grade of gas for $3-5 a tank extra.

You sound like a parrot.

I mostly agree with you but you can't see the exceptions worth shit.

My '00 OBW *doesn't* spec higher octane fuel. With a 10 to 1 compression ratio, that's pushing it. I've found that 89 over 87 gives me about a half-mile per gallon better, so if 89 is 10 cents or so more than 87 I fill it with 89.