Gasoline and Oil

[Hi Ho]

I never thought much about gasoline until I got a new car. I always thought "gas is gas". I don't know if I still think that or not. For some strange reason I have been buying mid-grade gasoline ever since I got my car. I used to buy the cheapest regular gas I could find (usually Arco) and seeing as how my old car has 356,000 miles on it I don't think that it did much harm.

However, I could have sworn that after I went through the tank that the dealer gave me (which I am pretty sure was Shell V-Power) and filled up with regular unleaded Safeway gasoline that my car didn't seem to run as smoothly. Ever since then I've been filling up with mid-grade gasoline paying about 10 cents more per gallon.

My question is, is this at all worth it? Is this the placebo effect at work? I know that the engine in my car was designed to run on regular gasoline and using anything more should be unessecarry and yet, I'm still doing it. Any advice would be welcome.

The other thing that I'm wondering about is oil. I am going to change the oil in my car soon and I want to go with a full synthetic. Does anyone have any recommendations in that area?

[glc]

1. You should not need anything more than 87 octane. However, if it runs NOTICEABLY better on midgrade, use it. Be wary of offbrand gas, it may be very low on additives. Arco is owned by BP now and it's good gas.

2. Synthetic oil is highly recommended. Use the manufacturer's recommended weight. I'm a big Amsoil fan but Mobil 1 EP is really good stuff too. If you want to extend the drain interval, use a high quality filter such as a Mobil 1 or Amsoil Ea filter.

[Brad the best]

if it's a new car with low miles then go ahead and use synthetic , however you have to commit to it because you can never go back .
castrol
mobil 1
royal purple (had a friend with a bad experience with it but most people seem fine)
red line
amsoil
there are lots of synthetic brands , you might also want to go to a more high end filter , like not a fram .

if your car is older you might see some leaks from the synthetic , normal oil swells the seals and gaskets and makes a good seal while synthetics don't swell seals . should only matter in a high mile vehicle
mid grade fuel usually is cleaner , regular is sorta from the bottom of the tank if you know what i mean .

it all comes from the same refinery , little differences in additives etc . mostly just aim for a newer station , i personally don't go to shell . in canada regular shell is 87 and husky or chevron's regular is 90 for the same price .

higher octane fuel just burns slower .

[Hi Ho]

Thanks for the advice. The car is new and has 2,700 miles on it. I've been going to Shell stations lately and it does seem to run smoother with mid-grade gas. That's not to say it runs rough with regular, it just seems more refined when running on mid-grade.

Does synthetic oil last any longer than regular oil or does the regular oil change schedule still apply? Now that I mention that, what oil change interval should I follow? The manual says has two maintainence schedules, 1 and 2. According to the conditions outlined in the manual I should follow Schedule 1 which says to replace the oil every 7,500 miles. I've put 2,700 miles on the car in one month. Should I still follow that schedule?

[TwoRails]

A very big Yes on gas makes a difference. Not only does it make a difference, but the same gas that make this car run good may not necessarily make your next car run good (meaning you'll need to check it to make sure). Saying all gasolines are the same is like saying all soda, or all bread, or all anything else are all the same.

[glc]

If you switch to Mobil 1 EP and use a Mobil 1 filter for example, you can go 15000 miles or 1 year between changes, but do NOT exceed the maintenance schedule while you are still under warranty unless the oil manufacturer has a supplemental warranty.

If you continue to drive that many miles in a month, 7500 miles is gonna come in 3 months.

Bottom line - synthetic oil is way more resistant to breakdown than dino oil, but you have to keep it clean. That's why you need a premium filter if you want to push the change intervals.

[David M]

Higher octane gas does burn slower and in doing so there is more time in which the burning of the gasoline is pushing against the piston. This creates a smoother push against the piston and therefore what you are probably feeling. Higher octane gas is also less inclined to pre-ignition (knocking)...which is also what you may be feeling. Modern cars have a knock sensor which changes the timing so that with higher octane fuel the spark ignites sooner as the piston is coming up....making for a little more power and smoothness.

Every car sold in the USA is required to be able to run on 87 octane. Car manufacturers have recommendations and not requirements for the higher octane fuels for their higher performance engines.

With synthetic oil you can actually save money if you consider the cost of going to an oil change place every 3500 miles versus going to an oil change place every 7000 miles using synthetic....even with the cost of synthetic being higher. Then factor in less engine wear and tear, greater engine longevity and a little better fuel economy using synthetic.

[thefultonhow]

I got a couple of cases of Castrol Syntec for my Infiniti. The new engine only has around 40,000 miles on it, so I figured now would be a fine time to switch to synthetic if I wanted to. Syntec is somewhat cheaper than Mobil 1, and since it's still synthetic, I can't see any problem with using it.

In terms of midgrade gas, if your car is designed for regular, it should run fine on regular. Running midgrade should not make it run appreciably better unless it's in need of a tuneup, so I think it's just a placebo effect. Now, if you bumped the timing, as you can do on older cars with distributors, or if the timing came bumped from the factory as it does on many higher-performance engines, the car would run better on midgrade or premium. Newer cars such as my mom's Audi run best on premium; they will retard timing to run on regular, but performance and fuel economy will both suffer. But other cars that are designed for regular will run pretty much the same no matter what; they won't take advantage of premium or midgrade's higher octane.

[TwoRails]

Ya, on some cars you can't tell a difference on grades of gas, but some you do. I sure can with my little truck. But, one thing that I do, and recommend, is to track gas mileage with your gasoline available locally. I get around 30 - 50 miles more on 3/4s of a tank of gas running 89 over 87. (And with a tiny tank like I have, that's almost a quarter tank difference!) That tells me that I get a better running engine on 89 octane. And that's after you run gas mileage tests to find which brand works better on your vehicle.

[glc]

You will also get better gas mileage with pure gas than you will with E-10, regardless of octane.

[Hi Ho]

Now, if you bumped the timing, as you can do on older cars with distributors, or if the timing came bumped from the factory as it does on many higher-performance engines, the car would run better on midgrade or premium.

This engine has variable valve timing. I'm thinking it's just the placebo effect but I'm going to try super premium next time I fill up just for kicks.

You will also get better gas mileage with pure gas than you will with E-10, regardless of octane.

That's one reason I'm not using Arco gas. It has 10% ethanol. The manual for my car says you can use gas with up to 10% ethanol but it doesn't recommend it.

[glc]

If you have a brand new car, it's set up for E-10. There are areas of the country where that's all you can get, there is no real gas any more. The Chicago metro area is one of those areas.

Your O2 sensors and ECU can probably handle up to about 40% ethanol before it goes too lean and throws a check engine light. Just don't try to use E-85 unless you have a flex fuel engine.

[Hi Ho]

Well the only gas that I know of in this area that is E-10 is Arco.

[glc]

Just for the heck of it, try some Arco regular grade - see how it runs and what kind of mileage you get. When I was out in CA I used it in my truck and it seemed to be as happy with it as with anything else. The reason it's cheap is they don't take credit cards and they nail you 45 cents service charge to use debit or ATM cards.

[Hi Ho]

That's the other thing about Arco. I rarely have cash and use my debit card for everything.

[hitchface]

I'd go for higher grade gas if you can, but more important is where you get it from. In my town, my options are Mac's or Shell. Even using 87 from both, the gas I get from Shell is noticeably nicer to my motorcycle engine. Since gas prices aren't an issue with that thing, I go premium all the time. On a 5 gallon tank I can snag about 190-ish miles using premium and some of my reserve. Not bad for a '95 Vulcan.

Anyways, higher grades are nicer, but pair up your driving habits with how much you spend on gas. If you do a ton of highway driving and suck up gas like crazy, premium might just be too expensive to consider.

[HAL9000]

I'm going to throw in a different argument here of "gas is gas"... now before anyone flies off the handle here with this statement, there are some specifics to it and I'm assuming I'm in a bit of a unique situation.

First of all, on every car I have owned, I have played with running through several tanks of gas regular and premium from different stations and have had NO difference in performance or economy.

Second, and here is where the unique situation comes in... we have a refinery here in town that is one of two that supplies western Canada. Shell, Esso, Petro Canada, FasGas, etc, ALL get their gas from that same refinery.. even the place we affectionately call "The cabbie joint" gets their deliveries from this same refinery (this is where I purchase from because it is at any given time anywhere from 4 to 12 cents per litre cheaper). There is only ONE place that gets gas from out of province and that is Mohawk that is an ethanol blend that comes out of the second refinery in Alberta.

The only differences I have seen in performance and ecomony in my current car (99 Pontiac Sunfire GT) is with the Mohawk gas... the milage is a small amount lower, but I don't see any noticable difference in how it runs or power.

So to me, gas is gas when it is from the same refinery and I can't justify spending the extra on premium when I'm not seeing any benefit from it.

[Brad the best]

i think i already said it all comes from the same refinery and the same dirt people are so shocked when you tell them that .

[thefultonhow]

Originally Posted by Hi Ho This engine has variable valve timing. I'm thinking it's just the placebo effect but I'm going to try super premium next time I fill up just for kicks.

I'm actually talking about ignition timing. That influences how complete a burn you get, so it has a decently large impact on fuel economy. On my Infiniti, the standard setting for ignition timing is 15 deg BTDC (before top dead center), but bumping it up to 19 deg BTDC by rotating the distributor will give you more power on premium, but may cause problems on regular. (Of course, that's just base timing. The various sensors will advance and retard timing at various times; I pluged a scan tool in at one point, and saw timing as high as 25 deg BTDC and as low as -5 deg BTDC -- that is, 5 deg ATDC -- over a short drive around my neighborhood.)

[glc]

TFH, he has a new OBD2 vehicle, there are no adjustments whatsoever that can be accessed by anything other than a diagnostic interface (essentially, reprogramming the ECU) - so what he sees is what he gets. The knock sensor does cause the timing to vary and it MAY run a bit better on higher octane - but is it worth the extra cost per gallon?

The reason it gets less mileage on ethanol added gas is it will run richer. The O2 sensors handle that. Alcohol requires a different fuel/air ratio than gasoline to burn properly but it has higher octane than gas. Add 10% ethanol to 87 octane gas and you get about 89 octane blend.

The gas may be coming from the same refinery, but different companies use different additives so there will be differences.

Bottom line - some cars are sensitive to octane and other factors in the fuel, others run the same no matter what you put in. Some drivers notice small differences, others don't. Every case must be taken individually.

[HAL9000]

The guys that I know working at the refinery say yes, there are additives put in at the time of delivery, they're pretty much the same, maybe slightly different quantities, but these additives won't be doing anything for performance. They're essentially detergents and moisture displacers. They're not anything that will be changing the octane rating itself. It's true that some cars will run better on a higher octane and there is usually a manufacturers recommendation for such. When I was in my hot rodding days, yes, the high compression engine and a few degrees extra advance on the ignition required premium to keep detonation from occurring.

[thefultonhow]

Originally Posted by glc TFH, he has a new OBD2 vehicle, there are no adjustments whatsoever that can be accessed by anything other than a diagnostic interface (essentially, reprogramming the ECU) - so what he sees is what he gets.

I know he can't alter the timing, but it's not because he's OBDII -- it's because he has distributorless ignition (either with a coilpack or a coil-on-plug system; I'm not sure which the Mazda3 uses). Many G20s were OBDII but still used the SR20DE engine with a distributor. In fact, the 2000-2001 Sentra had two engines -- the SR20DE in the SE and the QG18DE in the other trim levels. Both were OBDII, but the SR20DE used a distributor and the QG18DE used a coil-on-plug system, so the former could have its timing adjusted easily, but the latter couldn't.

My point was mostly that variable valve timing and ignition timing are two different things.