Premium vs Regular Unleaded Fuel

[hightest]

Hi,

I was wondering what everyone's thoughts are on running the engine on regular vs premium fuel. I have a 2006 XC70 and have experimented...
when I use regular fuel the engine light comes on...when I use premium it goes off... I thought the computer would adjust for it but I suspect I am wrong

Curious

[awise1961]

Your car should run fine on regular no-lead.
I have run both regualar and premium on my Wife's 2005 XC70 and both are accepted by the car.
However, we typically use premium as I find a slight performance edge (system advances the timing due to extra octane) and I like the extra cleaning that the comes with the chemicals associated with the octane boost.

When the engine light comes on, what code(s) does it throw?

Al. Wise

[hightest]

Hi Al,

I dont have a code reader...so I dont know the code...the engine starts to run rough and surge up and down and then the engine light comes on. When I filled up with premium and ran it for a few days the light went out. I then used regular unleaded and it happended again...premium made the light go out again a second time...hence my question. When I have the car in for service next week to replace my rear shock I will ask them to read the code (I assume it will be stored)

[Forkster]

That's very different... it shouldn't throw any codes using regular. I often use mid-grade in city driving and premium when doing highway travel or towing.

Regular fuel is fine, but as Al said, there is a noticeable performance loss using it

[atbspinner]

I've had my CEL on and off over the past few months. Code is on the cat. My friend at the local dealer (service manager) seems to think the addition of ethanol to our gas is causing early cat. failures. He has seen a spike in the last couple of years on even late model failures. No rock hard evidence but I try to stay away from gas with ethanol added.

[billr99]

I've had my CEL on and off over the past few months. Code is on the cat. My friend at the local dealer (service manager) seems to think the addition of ethanol to our gas is causing early cat. failures. He has seen a spike in the last couple of years on even late model failures. No rock hard evidence but I try to stay away from gas with ethanol added.
Not sure I buy that. They have been adding ethanol in fuel many years. I remember that BP in Ohio (when it was called Sohio) began adding ethanol around 1980 or so. I would think that any widespread ethanol-related failures would have been seen way before now.

Now if he wants to suggest that late model cats are being made to a lower quality level than in past, that's believable. Everything else seems to be heading that way, why not cats. In any case, I would look elsewhere for the source of your CEL. O2 sensors perhaps?

Cheers,

Bill

[haute]

That's very different... it shouldn't throw any codes using regular. I often use mid-grade in city driving and premium when doing highway travel or towing.

Regular fuel is fine, but as Al said, there is a noticeable performance loss using it

I have found the opposite, in terms of fuel economy.

Oddly enough, my fuel economy goes *down* when I run ours on premium. The best mileage I get is on regular.

Over a long highway trip, say a family vacation, things may be different though.

[jmoser]

Higher Octane premium fuel actually has lower BTU content than regular; you only need the premium for highest possible turbo boost under high speed / high load conditions.

It may be entirely plausible that mpg is lower with premium in city driving but I would expect on 70 mph highway trips that the premium enables the turbo boost to increase efficiency enough to make mpg better.

I have mixed regular, midgrade, and premium over the years with no issues but now stick with premium since 80% of my miles are 70 mph highway trips between Detroit and Chicago.

I was getting 28-29 mpg in the summer, now only 26-27.

[Chilled Man]

actually on most highway driving you dont boost at all ... unless your weaving in and out of traffic ?

[Mike_v]

I use regular in my 01XC and run an average of 17-18 mph (90% of the time non-highway, I estimate that about 60% of the miles are non-highway). On a 70 miles per hour long-range highway drive I'll average 24 mpg.

I have tried premium hoping to get more miles out of the gallon during non-highway driving but found no difference. Neither in gas mileage, nor performance.

[jmoser]

actually on most highway driving you dont boost at all ... unless your weaving in and out of traffic ?

If that is true then Volvo wasted a tremendous amount of time and $$$ designing and equipping these engines with turbos.

This is a passenger car [wagon!!] - not a race car. It should be calibrated for normal driving duty cycles including turbo efficiency gains at normal highway speeds.

Ford is scrambling to bring its 'EcoBoost' engines to market to reap the benefits of turbo derived mpg gains - you don't need redline RPMs to benefit from a turbo.

[Willy]

I tried both, since I don't use all the power of the engine, I don't feel any difference. The higher cost of premium
is balanced by the somewhat better fuel economy. I ended up using regular fuel and the car never complains ;)
The attached pdf is from the owners manual.
Willy

[Ocean Racer]

Willy, Do you use Sans Plomb 95 or 98?

[Giles]

I use premium unleaded (98 RON) in all my cars and even my wife can pick the difference in performance. The most notable difference is with my old Merc.

It burns cleaner and it does self clean the injectors.

To me it's a small price to pay for peace of mind.

Regards,

Giles

[Willy]

Willy, Do you use Sans Plomb 95 or 98?
I use 95 RON (loodvrij :)). The cleaning factor of fuel is not a function of the octane number as such,
but has to do with additives. It is not impossible that 95 and 98 have the same detergent mix, this
can differ between brands since these additives are not tied to legal ruling (at least not in my region)
Willy

[Ocean Racer]

ok, btw, I lived in Brussels all of last year [thumbup]