The manual recommends 91 octane but says 87 can be used. What are most people doing on the XC70 T5?
Bob

 

Most people are cheap and do dumb things when it comes to the care of their car, until something goes wrong that is. So most use 87. By law all cars have to be manufactured so that they can run on 87, that's why the option is there. The KNOCK sensor system in most cars allow them to run on 87 octane.

 

87 will not harm anything in your car. And there are cars that require premium. Sure, those will still run on 87. But damage can occur to those.

 

So does that mean we're running 91?

Bob

 

I run 87, it isn't going to hurt anything. I ran a few tanks of 91 and got the same MPG.

 

OK I didn't notice any problem with 87, but I'll try 91 for a few tankfulls for curiousity.
Bob

 

I run 91+. If you run 87 and have a knock system go bad, it WILL be bad for your motor.

I get better gas mileage on 91+. If you switch to 91+, you will likely NOT notice anything for the first tank or two because the computer takes a while to adjust to the higher octane fuel.

If you want more detailed information, just google something like "my car recommends higher octane fuel" and read up on it. A lot of VOLVO MECHANICS tell people to run lower octane fuel. Not sure why they would do that when the ENGINEERS recommend otherwise. Maybe they are smarter or make more money than the engineers that design the car motors.

Low octane fuel in a car that should have higher octane fuel can cause delayed problems which include burnt valves, carbon build up, fouled o2 sensors, sooner death to cats, and spark plugs that need replaced sooner.

All because a manufacturer makes a good knock system doesn't mean you should take advantage of it. You will notice it most when driving up hill with a loaded car.

 

Sorry, but that is straight up false information.

If what you are referring to a "knock system" goes bad (the P2s don't have problems with knock sensors), the check engine light will come on. It isn't like there is no warning. And it isn't like there will be immediate damage if a knock sensor does go bad. The owner's manual states specifically "running 87 octane and up will not affect engine reliability."


There is a difference between requiring 91 octane and recommending it. Volvos do not require it and will run fine with 87 without damaging anything. I've been working on them for a long time and never seen one come in with damage due to running 87 octane.

The dealer I work for has another car line which requires 91 in one of their engines. I have seen them replace engines with piston damage due to running low octane fuel.

 

Ive run high-test since the car was new....as the manual suggests.
Ive had minimal problems with fuel injectors....zero problems with turbo and always plenty of power.

My indy volvo guys claim they can see a difference in running high-test as opposed to volvos run with reg.....particularly as the car ages.

Its a typically 8-10 cents more per gal.

 

It's more like a 30 to 40 cent differential in my area to step up to 91 octane. Which is a couple $100 for the amount of drining I do.
Bob

 

First off, what part of my statement is FALSE? That most people run lower octane? That I run 91+? That mechanics like you are smarter than the engineers that design the cars? That mechanics like you make more money than engineers? That the car has a knock sensor that can fail (my buddy has one right now)? That piston rods can and do break? Etc...

Besides that, a lot of people have the CEL light on all the time, since they have purchased the car 3 years ago. They think CEL means "Clear, Everything Lovely". How will they know when another system goes unless the car starts running rough.

After you show me that, please point out where in the owners manual that specifically states that NO ENGINE DAMAGE CAN BE CAUSED BY RUNNING LOWER OCTANE FUEL.

 

What does the amount of money I make have to do with this?

Yes, plenty of people run 87. And guess what, it doesn't cause problems.

The knock sensor can fail, but, on the P2 anyway, it is VERY rare.

Page 121 of the 07 XC70 manual. I can't link because I'm on my phone.

You can run whatever you want, if it helps you feel better, great. But the fact is that simply running 87 octane is not going to damage anything. If it would, Volvo would not simply recommend running 91, they would REQUIRE it like some other vehicles do.

 

This is a good read

 

I was running Bp 87 but read my book again and it said 91 was also recommended for 2008 v70. I put in over a half of tank of premium BP 93 octane. Hiway mileage jumped 3mpg to 26 mpg at 75 to 80 mph. Yes it is 30 to 40 cents per gallon more but I intend to keep this car a long time so i think it is worth it. This is the nicest car I have ever owned except for maybe my Nissan Maxima Wagon with the 280Z engine.

 

I found that I also got better mileage with 91+. The cost/better mileage actually more than offset the cost by 5%. My gas bill dropped 5% even though I paid more for the higher octane fuel. So, in MY opinion and MY experience, it was cheaper to use the RECOMMENDED fuel grade. (@ES6T: I can send you my notes, receipts, and graph if you'd like.)

 

I don't need your notes. I'm not arguing that you could see better MPG. You make it sound like running 87 is causing engine damage, which is false.

I ran 91 and my mileage was the same (give or take .5 mpg) over 5 tank fulls.

 

I agree with rspi. I always run Shell V Power in everything I drive. The 40 or 50 cents per gallon difference results in a cleaner burning engine and better mpg, and easier on the valves. I was in the Auto Business for 32 years and have seen the results of build up and piston slap from running cheap fuel. It's worth it in the long run to stick with the highest octane you can get. The premium fuel now available is like the regular of 20 years ago.

 

The detergents are totally different than octane. 87 is no harder on valves. It doesn't burn "cleaner".

30 years ago was much different with regards to both fuel and fuel injection systems.

 

Piston Slap is due to Low Octane, and yes fuel was different then...No EPA meddling. I'll stick with Supreme.

 

No its not. All engines have some degree of piston slap. Piston slap is the side to side movement of the piston as it goes up and down. This is because there must be some clearance between the piston and cylinder bore, otherwise it couldn't move. Excessive piston slap is due to engine wear. It has nothing to do with octane.