In the November issue of Consumer Reports, the "reality check" article seems incomplete to me. It says if your car is designed for regular-grade fuel, don't waste your money on premium grade as it won't improve performance. I believe the caveat that should have been mentioned is that there may be the benefit of better mileage.

As has been discussed in this forum before, mileage may vary with the grade of fuel used. In my case, although my '99 Saab 9-3 owner manual recommends "minimum 87 AON, unleaded gasoline", when using 89-octane Plus grade, my mileage increases more than enough to outweigh the additional cost per gallon. The 93-octane Super gives a further boost, but not enough to be cost effective. Other Saab owners report similar experience.

Perhaps Saab is unique in this aspect. However, I doubt it and would not have discovered this except that I noticed a very slight knocking while climbing steep hills (something we have here in Seattle). As a result, I experimented with higher-grade fuels which eliminated the knocking spells and increased mileage.

Given the high cost of gasoline and the geo-political and environmental impacts of its consumption, we should all be looking for ways to improve fuel economy. Maybe experimenting with different fuel grades would help other CR readers. Of course, that would be easier if all cars were equipped with a readout (gauge) for fuel mileage.

Brian

Perhaps we could have been clearer.  We say " if your car is designed for 87-octane fuel, don't waste money on premium". The key words here are designed for. Some cars, like your SAAB are designed for premium fuel. In higher compression engines premium fuel gives more power. Though the engine can run on a lower grade of fuel, this capability is due to automatic detuning by the engine management system to prevent "knocking" which can cause damage. With the engine not running optimally, mileage can suffer.

Thanks, Jerry for your explanation.  My Saab is a higher compression ratio (9.2:1).  Interestingly, the owner's manual, sales brochure and Feb '99 Consumer Reports all talk only about Regular(87 octane) fuel.  So I think my car is on the border line.  Perhaps carbon build up has pushed it over the line to really needing Plus-grade. Anyway, what I take away from my experience is that frugal car owners might want to experiment with a higher grade and just to see if they get more miles per dollar.

would not have discovered this except that I noticed a very slight knocking while climbing steep hills (something we have here in Seattle). As a result, I experimented with higher-grade fuels which eliminated the knocking spells and increased mileage.

Note that knocking on a recommended octane but not on higher is often a sign of deteriorating engine performance. On some models, a stretched timing belt or chain can affect not only valve timing and accuracy, but also ignition timing. Worn plugs can cause a weaker spark. Eg. Under these circumstances, using a high octane fuel can definitely improve mileage, but that is just masking the underlying causes.

Steve

Thanks, Steve. I'll keep your remarks in mind the next time I take my car in for service and have the mechanic look for performance problems.

Brian

I distinctly remember reading in a car magazine the advice that cars need slightly higher octane as they grow old.  Where does CR weigh in on that ?

NOt sure where they weigh in but in modern vehicles with excellent engine controls and that is kept in good condition absolutely not necessary

Yo Larry

OP did say 10-year-old car that does knock on hills -- and doesn't with premium. Not taking anything away from you or anybody else but there it is. I don't know where your personal cut-off on "modern" may be.

THan it's obviously got a "problem" using premium does not "fix" the problem it only covers or masks it. THe underlying problem is still there. Careful diagnosis is needed. A NORMAL engine should work fine for its entire life runiing on what it is designed to run on. If it does not than something is wrong