Volvo 850 - gas type?

None do. They may perform better and get better gas mileage with premium, but they have a knock detector that will adjust the timing to the grade of the gas. I have had a '93 and '95 850 and a '01 V70XC and never used premium in any of them. No problems. I like to run a tank of Chevron with Techron every once in a while, or get a can of Techron and add it myself, but never had any problems.

My '95 850 manual says: "Volvo engines are designed for optimum performance on premium with octane AKI 91 or above (AKI = RON + MON/2). Minimum octane requirement is AKI 87."

This implies that although 87 is OK, the higher (premium 91 or above) would be 'better', yes? Any harm done in alternating tankfuls, or should I just stick with one rating?

Jay

It's about efficiency. The knock sensor will adjust the timing OK, but it is compromising an engine that was designed to be able to use premium, so it will necessarily make the engine less efficient - less power and less mpg.

Depending upon the price difference between the grades of fuel, you may actually find it cheaper to run on the more expensive stuff. There wouldn't be any point in alternating tankfuls.

Actually, if one didn't let the tank go dry between fill-ups, alternating tankfuls would raise the average octane level, since there would be at least some 91 octane in there with the 87.

I don't know if I would waste the effort. 20 cents more for premium times 15 gallons is $3 per tankful difference if it's completely empty. I would spend the extra for increases performance. KennyH

Horsepower is cheaper than therapy.

...or lower it.

You've made a direct hit, I think--and the logic of your argument is even more persuasive here in Europe.

Not sure what you're paying but not long ago we heard the shock! horror! stories of 'two bucks a gallon for gas!' in America so let's use that price for the purpose of illustration. If regular is $2.00 and premium is '20 cents more', then your '$3 per tankful difference' represents a

10% increase.

In Finland (where I am), today, a typical price for regular is 1.159 euros per litre and for premium it's 1.189 euros per litre. That translates (at today's exchange rate) to US$ 5.35 and 5.49 respectively, per US gallon. The price differential here is only 2.6% more for premium.

Assuming your 15 gallon ( = 57 litre) fill, that's $80 for regular and $82 for premium. Does it make any sense to scrimp for a lousy two bucks per tank, on a bill of 80 bucks?!? My '95 850T is happier on premium, and when my Volvo is happy, I'm happy. :-) (Of course, I'm one of those guys who changes oil every 3000 miles, too.)

One last point: you say '15 gallons...if it's completely empty'. The tank capacity on my '95 is 73 litres, which is more like 19.3 gallons. Maybe the US models were different?

cheers,

Henry

Your manual says it all. No harm will be done if you stay at or above

1. There is no point in alternating. What would make a more sense would be when you fill up to use part one octane and part the other IF you saw a difference. Gas stations don't have a rule that says you can only use one grade. You can mix grades at the pump. You will have to pay twice at a "pay at the pump" station, but who cares if that is what you want.

Your manual just says you will get better power and, perhaps, better economy from 91 octane or better. The experts, "Click & Clack," say to use the grade that gets the best miles per $ for you. Any better grade is just a waste of money.

My '65 Austin Healey Sprite would get 30 mpg on regular and 35 mpg on premium. It turned out I got the same miles per $ no matter which grade I used. I haven't notice that effect with my Volvo 850s.

Has anyone ever done a test - see the mileage difference on a base 850 with 87 then with 91?

There is a difference of abotu 20 cents/litre of gas here. I think one US gallon is 3.8 litres. The difference is substantial - but if mileage was equitable - it might be worth it.

Anyone try this or have info on where I can find this info?

Thanks,

Tmuld.

You're all forgetting the altitude factor as well. At 5280ft our pumps all offer lower octane levels.

Can't say on an 850, but my '95 Passat VR6, over 100 miles of comparable driving was only about 2 MPG better....not enough from an economy standpoint.

Ron/Champ 6

1963 8E5 Champ (Champ 6) 1962 Lark Daytona Convertible (Boomerang) 1995 VW Passat (Vanilla..yuk) 1994 Volvo 850 (Tilley)

Ron/Champ 6

1963 8E5 Champ (Champ 6) 1962 Lark Daytona Convertible (Boomerang) 1995 VW Passat (Vanilla..yuk) 1994 Volvo 850 (Tilley)

There's an exception. Turbo engines, like my 850's, have their maximum boost limited by the output of the knock sensors. So, higher octane = less knock = higher boost = more power.

To reply, please remove one letter from each side of "@" Spammers are VERMIN. Please kill them all.

Think out of the box. Try mixing 87 and 89 if 87 doesn't work as well as 89. If that is not a problem, then stick with 87.

lower octane = more knock correction = lower boost = more economy.

I have with both my '93 and '95 with highway driving and saw at most a one mpg difference between 87 and 91 octane. Definitely not significant.

In terms of pure economy, it all depends upon the price difference between the grades of fuel. A turbo is not about simply chucking more fuel into the engine.

The more boost (or compression) you are able to employ, the more efficiently the fuel will burn, which means extracting more usable (kinetic) energy out of the same amount of fuel. This is a fundamental principle of engine design.

The limiting factor is the ability of the fuel to withstand the initial combustion pressures without detonating spontaneously before the flame front reaches it. This is what we usually hear as knock, although there can be other causes for it, too. An engine will be designed to use a fuel that will not detonate at a given maximum pressure. This is governed by compression ratio and turbo overpressure. If lower octane fuel is used there is a danger of knock, and in order to prevent this, the ignition point is retarded so that P[max] occures later in the descent of the piston and will consequently be lower. This will result in relative inefficiency.

An engine that needs to retard its ignition timing to prevent knock is not using the ideal fuel to exploit its combustion pressure fully, and cannot be working at optimum efficiency.

Most drivers tend to use the extra energy that a turbo releases as HP rather than torque (many turboed cars are set up to maximise this), which may mitigate against achieving greater mpg. One problem with turbochargers is that they don't start working well until they are spinning fast, so at lower speeds, running less boost, a turboed car (which often tend to have lower compression ratios) will be naturally inefficient.

And in the real world a turbo'd gasoline engine will almost always get worse fuel economy than the same engine without a turbo. Both of mine get several mpg lower than the N/A Volvos in the family even driven conservatively. Worst economy is on regular, mid grade gets the best mileage, and premium allows a bit more power for around the same mileage as regular, I usually run mid grade. The 240 has no knock sensor and pings on regular at 14 psi so this mostly applies to the 740.