Hey again!

This is for my 02' C70 Turbo Convertible (90K miles). I need an honest answer on the octane I'm really supposed to use on it. I know the owners manual says a minimum of 91, which in Florida would be 93 octane (its our highest) since it goes 87, 89, 93 but everywhere I have read, people say they use 87 in theirs all the time and never experience problems.

I dont have a problem using the 93 octane if thats what I'm supposed to do but my questions is, if the previous owners used 87 like everyone else out there seems to do will switching over to 93 hurt the car or do I need to work my way up? I know in my Jeep Grand cherokee I was told it was BAD to use a higher octane gas.

I read that people who used to use 93 who then dropped to 87 actually noticed increased gas mileage. If this is the case, after switching to 93, will it hurt the car to go back down to 87 if I notice a loss in gas mileage?

In other words, does switching octanes at 90,000 miles hurt the car??

Thanks!

 

Use what ever you want. Running premium will yield the best performance and mileage, but in the real world it's not an absolute must.

 

Your car is designed to run on "premium" fuel. This means, in most cases (I am new to Volvos...) 91 octane. There are some stations in FL (i.e. some 7-11's, etc.) that reatil 91 Octane fuel in addition to 93. You can even blend your own, if you're a true spendthrift by filling an empty tank >50% with 89 octane and the balance with 93. Though the trouble will save you minimally. Nonetheless, the majority of the time you will most likely run 93 octane to achieve "optimum performance". That being said, nearly every "newer" car that requires higher-than-regular octane is also equipped with a knock sensor. This sensor has the ability to sense the detonation (pre-ignition) caused by lower octane fuel (knocking, or "pinging") and automatically retards the ignition timing to compensate and eliminate any detonation. Now, as a result of this timing retardation, the engine will still run fine, albeit with a reduced power output. Furthermore, as a result of that, one could potentially see increased fuel economy for one of two reasons: 1) you are driving more modestly because you know the maximum performance your car is capable of is unavailable and 2) in some instances, the timing retardation in and of itself can reduce the fuel supply (think of it as a lower-performance setting...less spark and less fuel to go with it). All of that said, any gain would be negligible, though I suppose potentially measurable. As far as it being "bad" to switch from a car whose diet as been mostly regular and going to premium, or vice versa for that matter, it shouldn't make any difference. If your knock sensor is operating correctly it will compensate for a change in the octane in fuel you provide it either way.

Conclusion: If you're a cheapskate, you can run regular, and you'll be fine. Just a tad bit slower. But honestly, when you consider all your expenses on the car, if a couple dollars savings per tankful (maximum) is REALLY that important, maybe you should purchase a less-expensive (i.e. Hyundai Accent) car. My take, even if you're low on the cash - run the good stuff if that's what your car is designed to burn (and yours is). Or else all the other monies spent on your SwedeSled are partially wasted.

 

Over here 93 octane is standard and we can get 97. Doesn't make much difference to the performance but the MPG get a little better. I can get 28 in town and 35+ highway (that's on a 9 US pint gallon). If only I could afford more gas. How does $8 a gallon sound to you??

 

Expensive. Also a US pint is 16oz., so it is 8 in a gallon(128oz.).

 

My 2008 v50 gets better mileage with 91 octane than with 87. However, 93 does not get better mileage than 91.

 

Yeah, but there are imperial gallons, too. I think that's what he's talking about, and they are 144oz.

 

Most likely the unit he is using considering location. At a glance though it looks like a statement of fact. Besides, thought they used pounds across the pond.

 

I get same fuel econ on 87 or 93 for highway mpg. I noticed decrease in power for 87, it won't brake the wheels loose as much during first gear acceleration now. When you drive as much as I do, that $5 difference per tank really adds up.

 

The manual says that 91 is recommended, 87 minimum.
https://www.customers.volvocars.com/...c_04a.htm#pg64

All of my cars recommend the same. I usually drive 40,000 per years so I feel I can safely say I know the pain. I can feel little difference in power but I get better gas milage with 91. I also use a Scan Gauge to help me monitor milage.

I will add 1 important note. I have read that mechanics say that lower octane gas can cause other long term effects on the motor. They claim that they see a LOT of BURNT VALVES in cars that run 87. So, you may not see a problem now, but 40,000 to 50,000 miles down the road you may pay dearly for the lower octane gas.

I get 15 to 20% better milage with 91 (actually it's 93) so the price difference is offset by far with better milage. Our 93 octane is about 7% more expensive and I get 15% better milage, it's a no brainer to me.

 

As for the 91+ octane... I've alway wondered about that and recently seen a car TV show with some guy with a hot rod (old vett) explain that issue. The thing is that some cars with smaller motors design them to preform better by raising the compression ratio. If you use lower octaine gas in a car that runs compression over 9.0:1 it runs the risk of knocking. What the guy said was that a lot of car companies, mainly the ones that produce preformance cars, have high compression, some over 10.5:1.

What happens is the fuel injector sprays fuel in the chamber and the fuel is waiting for spark to create the explosion. Well, as the compression in the piston gets greater, lower octane gas has a lower flash point and may ignite before the spark is given. If this happens the chamber will get a premature ignition and cause the piston to receive the entergy before the spark gives it causing a knee jerk reaction that is called KNOCK (some men experience this with their lady friend, not good for that situation either). Now Volvo's have 2 knock sensors and do their best to avoid this situation/problem. The US Gov website advises people to knotch up the octane if they suspect or feel their motor is knocking, one level at a time. Volvos do a good job at preventing knock, however, if one of those knock sensors malfunction and your motor starts knocking, you can cause problems with your motor. I can't prove it, but I bet some people that are complaining about their car missing or running poorly have knock problem. The thing is that they would have to pump 91+ and run out the 87 to figure it out.

Now, I always thought that it was more important for a higher preformance motor to use 91+ octane, like the turbo since it put out more hp. Well, the fact of the matter is that the N/A motor is actually a higher compression motor, it has to be just to make it peppy with no turbo. If you look at the Volvo site, you will see that the specs of the motors are as follows when it comes to compression:

2.3 T3: Compression ratio 8.5:1
2.5 T: Compression ratio 9.0:1
2.5 NA: Compression ratio 10.5:1

https://www.customers.volvocars.com/..._133.htm#pg135

The 960 is even worse. It runs Compression ratio 10.7:1. I put some gas in the car one day and it would not drive over 45 mph until I ran down that gas.

Of all the cars, the T5 has the lowest compression.

Your car, you can do what you like. I do run 91+ mainly because the owerns manual recommends it and I think I get better mileage with it. You may not experience the knock with low octane gas unless you put your foot in it, not sure if there is any immediate price to pay but you will end up with burnt valves and maybe even worse, bent valves. I've also read about people compalining about their timing being off. I wonder if they are knocking. I also see a lot of people complaining about their car not wanting to rev above 4k. Makes me wonder if they put some octane boost in the tank will it make a difference.

 

The on board computer adjust the timing & spark etc based on the sensors determing the octane being used on all gasoline vehicles with OBD II. Better performance with higher octane when the vehicle manual states the higher recommended octane. Lower performance with lower octane.
The most important vehicle maintenance includes: oil/filter changes, spark plug changes, oxygen sensor operation, cat converter operation, good radiator fluid, good transmission fluid with filter changed. Inspecting differential fluid in high milage vehicles is recommended. No codes means minimum requirements are being met. Following vehicle maintenance requirements is vital to long vehicle usage & all parts wear. Preventive maintenance is cheapest vehicle operation exspense! I would take rspi advice! Seen fouled plugs, clogged EGR valves, dirty MAF sensors with low octane. rspi is right it is a pay me now or pay me later situation! Later can be exspensive! Waiting for the turbo to spool down when parking a couple seconds also can prevent coking of the turbo, gas or diesel.

 

i'll be honest in saying that i don't know the technical side of it but i always run the high test (93 octane)in my c70 with 148k on it. but the 1 time i wasn't paying attention and filled it with 87 octane (wasn't thinking about what car i was filling, since my gp runs on regular) it ran rough compared to the high test stuff.
if you are worried about running the cheap stuff get a n/a car to run the cheap stuff in for your DD and use the volvo for your nice weather car