Regular gas for Volvo?

MY 2000 S40 is supposed to use medium octane gas, but I always use regular. It runs fine. The computer adjusts the engine for the difference. I occasionally notice aslight improvement in performance after filling the gas tank, and I figure there was a surplus of the higher octane gas, so it was being sold as regular -which is perfecly legal. The difference in performance is barely noticable.

I once car pooled with someone who used regular gas in a car that really did need higher octane. The car knocked terribly, which does put a strain on the engine.

Here in Nevada our fuel is a point lower than in Cali. I can get away with using mid-grade when it's cold here in Las Vegas but when the temps start to increase I have to go back to premium. One thing that I did notice a couple of years ago is that if I use regular or mid grade during the Summer and hold the transmission in gear with Geartronic at about 3,500 rpm the engine developes a definite surge that disappears with going back to Premium. My XC70 was a European order, if that makes a difference. The dealer looked at everything and said that therre were no codes. Although, my history with the dealer would indicate to me that there might be something wrong and they just want it to break so that they can replace it.

I have used regular grade in all my Volvos since the 544s. Of course, back then fuel was leaded. When unleaded came in, I was concerned for my then 145 but nothing bad happened. With modern cars, the computer that controls engine function adjusts to the fuel used to control the timing appropriately. Some argue that they get higher MPG with higher grade fuel but studies have shown the trade-off isn't worth it for the price difference.

There is no good reason to buy more than 87 octane.

Chuck Fiedler Nothing but Volvo since 1974

Well, I did my own study comparing 93 with 89 octane in my S-40 and S-60. Mileage was down using 89 so it turned out that the price difference was only 2 to 3 cents per gallon.

I'd be nervous about running anything other than premium in my '82 244 Turbo.

Aftermarket "built" turbo, "built" head, rebuilt engine.

That engine was originally designed for European conditions, where the most common fuel is (and was in 1998) 94 - 95 octane. Most European manufacturers continue to recommend the target fuel in other markets for liability reasons. You will see a performance drop if you use 89 octane, but it sounds like you're using it anyway; dropping again to 87 might be too far adrift from Volvo's expectations.

Just what do you mean by a "Built Head"? Usually when they build a head, it means that the chambers are polished, or even dimpled all around like a golf ball, which causes the "swirl" in the chanber to slow down and burn more efficiently by eliminating the cold spots. What are you exactly talking about as far as the head is concerned? If it concernes milling, that can do nothing but cause more detonation, particularly with a 240 and no computerized retard.

My '84 Two Door Turbo runs fine on Mid-Grade, here in Las Vegas. The head has never been off, and I'm sure that there's a lot of carbon built up there. Only 134K, but some of the sensors are going, especially that heat sensitive, vacuum powered sensor under the manifold that has a cracked vacuum port. Hey, what do you want for 22 years old? I wish that I could say that for my '03 XC70. Fuck that piece of crap! My XC is the absolute WORST car that I have ever purchased...and I have had 12 NEW Volvos since 1967...When I had to have my parents co-sign for me because I had no credit.

OK, So I'm off my soap box, alright?

I see a big MPG difference with our 850 and 940 when I use regular. They run better on premium too...YMMV (in more ways then one) :)

I have never used premium gas in any of my 10 Volvos and never had any problems.

"Just what do you mean by a "Built Head"?"

Three angle valve grind

Upgraded springs / hardware

Polished

Basically, the head was built by a friend of mine at Aluminum Cylinder Head Rebuilders in PDX; he rebuilds aluminum heads day in, day out, many are modified and beefed up for racing.

He said he did some trick stuff, some race stuff, and the few I referred to are what I recall.

He didn't match the head to the manifolds, alas...

roll dem bones

I have used regular in my '98 V70 with the regular non-turbo engine for almost 100k miles. However I recently switched my '99 XC (low-pressure Turbo) from high test to regular and the gas mileage has gone down a little bit, enough to offset the savings. Anyone else notice this with their Volvo's?

Pete

doesn't the V70 use regular? (unless it's a turbo?!?)

I thought the 850/70s used regular on the base engines.

I'd check the manual, my 760 runs 87, RM, not RO method.. (I forget which is which, but the manual explains both, and gives fuel recommendations for both)

I could have sworn that I read in my 'sis V70 manual that it runs regular.

It'll work fine, you may get slightly poorer fuel economy but experimentation will be needed to see if it's poor enough to not save you money. Just get it from a decent station that doesn't have old contaminated tanks.

If he drives mainly on level ground and doesn't need all the power the engine can give with premium, he should get better fuel economy on regular, not worse. Regular vaporizes more completely, which can cause knocking if the knock sensor isn't working, but under normal driving conditions fuel economy should go up about 2mpg. Regular grade is also better for cold starting in Winter, for the same reason.

You are saying the level ground bit because you are expecting the regular fuel to knock or ping. It doesn't. I have used regular gas in all my Volvos for 41 years with no ping or knock. They go up hills and accelerate great on regular.

The fuel economy is better with premium in cars that are tuned for premium, but usually it is a complete wash as to how much you pay in $/mile in such vehicles.

What you are trying to say is that regular fuel is more explosive, not vaporized more completely. The explosive nature can cause a knock or ping if the timing is not right and the piston has not yet started its down stroke. Premium fuel burns more uniformly and less explosively and will tolerate being detonated before the piston has started its down stroke.

There are not nearly as many different fuels as their are different brands. They fill up a just a couple of different fuel terminals and then add their own additives. So most of the gasoline is the same and the only difference is the additives.

Both premium and regular fuel are both more volatile in the winter and less in the summer to prevent vapour lock. Most brands use the same fuel for both regular and premium and just change the additives. The most popular additives include aromatic hydrocarbons, ethers and alcohol (usually ethanol or methanol).

Oxygenate blending adds oxygen to the fuel in oxygen-bearing compounds such as MTBE, ethanol and ETBE, and so reduces the amount of carbon monoxide and unburned fuel in the exhaust gas, thus reducing smog.

Methylcyclopentadienyl manganese tricarbonyl (MMT) has been used for many years in Canada and recently in Australia to boost octane. It also helps old cars designed for leaded fuel run on unleaded fuel without need for additives to prevent valve problems. However, US Federal sources state that MMT is suspected to be a powerful neurotoxin and respiratory toxin.

I think it still comes under the heading of "try it and see." I've seen reports that fuel economy improvements were enough to offset the cost of premium, and others that they saw no difference at all. Sometimes the type of driving is important, too - cruising on reasonably flat highways might favor the cheaper grade.

Mike

Also there are more moles of hydrocarbon in a given amount of regular the premium b/c of the additives that raise the octane level in high test displacing some of the stuff that goes boom...but at least in my experence the furthe advanced timing ond whatever else the computer does when the knock senso does not go off makes both our 97 850 w/o turbo and the 94 940 with turbo get better MPG in real world conditions with premium...Go figure!

No, that isn't what I'm saying. I'm saying that if you climb hills using regular grade, the lower HP the engine produces will require more throttle opening, and you'll use more gas.

It's better only in exotic vehicles, or in cases where the engine is getting a workout. In vehicles with knock sensors, driven gently, regular should give better fuel economy. You don't see this said much because most people have a lead foot.

It's "more explosive" precisely because it vaporizes more completely. The same characteristic of Premium that makes it 'burn more uniformly and less explosively' also makes it yield somewhat less energy per ounce.

Even if premium is made more volatile in the Winter, it is still

*relatively* less volatile than regular. So you will still get the best cold starts in Winter with regular.