What happens if I use Unleaded instead of super?

[falmouth3 Senior Member Find all posts View Profile Close falmouth3]

I recently read an article on how to save money on gas. One of the suggestions was to try regular gas even if you manual suggested using premium.

We had a van years ago that was supposed to use regular but we had the pinging unless we used premium. We did a cross country camping trip for 4 months in that van and averaged something like 73 cents per gallon for premium - and we felt we were being ripped off when we got to Nevada and had to pay 90.9 cents. Those were the days. But I also made about $12,000 a year then, too.

Sue

[T. R. Oglodyte Moderator Find all posts View Profile Close T. R. Oglodyte]

And then there are the cars that keep running after you turn off the key. I had one like that. Luckily, it didn't do that often. Kind of exciting, never knowing if it was going to blow up or shut off.

That's called dieseling. It occurs when there is a carbon buildup in the heads. During engine operation the carbon heats up. When the engine is turned off, the carbon is hot enough to combust the fuel mixture. Automobile engines are normally shut down by turning off the ignition. When dieseling occurs the carbon deposits continue to provide ignition, and the engine continues to operate even though the ignition is off.

The solution is to get the carbon deposits out of the heads. Carbon buildup occurs most often during city driving - stop and go driving at low speeds. Extended operation at steady freeway speeds will usually clean out the deposits - that's always been sufficient for me. I'm sure there are other remedies if the freeway driving doesn't solve the problem but I've never had to worry what those added steps might be.

Keeping your engine tuned up will also help prevent dieseling.

[camachinist Super Moderator Find all posts View Profile Close camachinist]

A couple helpful hints from a mechanic (and racer):

99% of the time regular unleaded is fine. It's more important to get quality gas. I've seen formulations that are absolute crap. When you use regular instead of premium, the sensors on the engine will observe changes in the combustion process and adjust fuel delivery, ignition time and, in some cases, cam timing, to compensate and bring the engine within proper operating parameters. Usually, this means, using regular, a bit lower engine power, lower fuel mileage and marginally different operating temperatures. The engine management systems are designed to do this.

Regarding "pinging", it is briefly noticeable as the EMS adjusts to eliminate improper flame front propagation. I can hear it, even in a well-managed engine, because of experience. I can hear how the computer changes things in response to throttle and load and temperature conditions, simply because it responds (it can't foresee changes) and those responses take a fraction of a second. Pinging isn't damaging if it is rectified quickly, before it moves from detonation into pre-ignition, which can damage parts, especially valves, aluminum heads and aluminum pistons.

"Dieseling", or running after, has largely been eliminated, simply because most modern engines are fuel injected. Turn off key, fuel pump stops, injectors don't signal, so there isn't any fuel to injest and ignite. The problem was more prevalent with older carbureted engines, especially when smog controls were in their infancy, since there was a ready supply of fuel to be sucked in and burned, even if the ignition was off, as long as a source of ignition was available. Throttle solenoids, which closed the throttle blades completely when the key was turned off, cutting off most of the air, solved much of the problem. Since I operate older carbureted vehicles, it's still an issue for me, and is more prevalent with regular fuel than with premium. It shouldn't ever be a problem with newer vehicles. My newest vehicle, built in 1984, is fuel injected and has never dieseled.

BTW, I can use pump premium in the engine in my race car and, due to the extremely high compression ratio (over 13:1), it will ping at idle with no load. This is purely an instance of cylinder pressure overwhelming the knock rating of the fuel. Hence the need for a special fuel (racing fuel) for such engines.

Hope that helps!

Pat

[T. R. Oglodyte Moderator Find all posts View Profile Close T. R. Oglodyte]

I knew I was missing some details Pat. Thanks for filling in.

[BocaBum99 Super Moderator Find all posts View Profile Close BocaBum99]

A couple helpful hints from a mechanic (and racer):

99% of the time regular unleaded is fine. It's more important to get quality gas. I've seen formulations that are absolute crap. When you use regular instead of premium, the sensors on the engine will observe changes in the combustion process and adjust fuel delivery, ignition time and, in some cases, cam timing, to compensate and bring the engine within proper operating parameters. Usually, this means, using regular, a bit lower engine power, lower fuel mileage and marginally different operating temperatures. The engine management systems are designed to do this.

Regarding "pinging", it is briefly noticeable as the EMS adjusts to eliminate improper flame front propagation. I can hear it, even in a well-managed engine, because of experience. I can hear how the computer changes things in response to throttle and load and temperature conditions, simply because it responds (it can't foresee changes) and those responses take a fraction of a second. Pinging isn't damaging if it is rectified quickly, before it moves from detonation into pre-ignition, which can damage parts, especially valves, aluminum heads and aluminum pistons.

"Dieseling", or running after, has largely been eliminated, simply because most modern engines are fuel injected. Turn off key, fuel pump stops, injectors don't signal, so there isn't any fuel to injest and ignite. The problem was more prevalent with older carbureted engines, especially when smog controls were in their infancy, since there was a ready supply of fuel to be sucked in and burned, even if the ignition was off, as long as a source of ignition was available. Throttle solenoids, which closed the throttle blades completely when the key was turned off, cutting off most of the air, solved much of the problem. Since I operate older carbureted vehicles, it's still an issue for me, and is more prevalent with regular fuel than with premium. It shouldn't ever be a problem with newer vehicles. My newest vehicle, built in 1984, is fuel injected and has never dieseled.

BTW, I can use pump premium in the engine in my race car and, due to the extremely high compression ratio (over 13:1), it will ping at idle with no load. This is purely an instance of cylinder pressure overwhelming the knock rating of the fuel. Hence the need for a special fuel (racing fuel) for such engines.

Hope that helps!

Pat

Thanks, Pat.

You had me at "99% of the time regular unleaded in fine."

[PigsDad Senior Member Find all posts View Profile Close PigsDad]

My Lincoln truck and my Caddy both have the sticker that says 91 or above by the gass cap.

Might have a problem here in Colorado. (see below)

(do they even sell gas with less than 87???).

Yes they do. Here in Colorado, the regular is 85 octane, the super is 89, with mid-grade being 87.

With the higher altitude, engines do not need the higher octane. This really throws flat-landers for a loop when they come here.

Kurt

[jfitz Member Find all posts View Profile Close jfitz]

My Lexus GS300 from 2001 tells me super unleaded only. That's $4.25 today here in San Diego. What happens if I put in the middle grade unleaded instead? Will my car combust?

The engine control computer in your Lexus, as well as the computers of most modern passenger vehicles, will automatically retard the timing
to compensate for lower octane gasoline and prevent engine damage. Dropping down a grade of gasoline will result in a slight loss of performance. Since engines vary, it is possible, but unlikely, that the engine control computer might not be able to sufficiently compensate resulting in premature ignition.

Try dropping down a grade and listen to the engine over several tankfuls of gasoline. If you hear more than slight pinging under load, return to the higher octane gas. It is important that you do this over several tankfuls, preferably from several different vendors. Why? Because the pump octane is the minimum guaranteed octane of the product. In the case of regular and mid-grade gasoline a particular batch may have a higher octane than shown on the pump.

[4ARedOctober Super Moderator Find all posts View Profile Close 4ARedOctober]

We use regular unleaded 87 on our BMW 528i and our Ford Explorer. We have no problems with either.

I had a friend who worked at the local refinery for Arco and he told me that many times they produce the only highest octane and sell it for all three grades. It was a production issue at the time and they saved money by doing it this way. I am not sure if this is still true or not.

[M. Henley Class President Find all posts View Profile Close M. Henley]

87 Octane

I always put 87 octane in Rita's Chrysler 300, SRT-8, with a 465 Horse engine. Have had no trouble in 45,000 miles.

[dougp26364 Senior Member Find all posts View Profile Close dougp26364]

+++++++++

Re which brand of gas to buy. Whatever gas is sold in your area comes refineries that are local to your area - or via a pipeline that delivers a variety of products. If there are Shell stations in your area and there isn't a Shell refinery within 500 miles, the gas at your Shell station is not coming from a Shell refinery - it's far more likely to be coming from some local refinery. Sometime when you are near one of your local refineries and can see the truck racks, look at the variety of trucks being filled at the racks.

That was my arguement as well until they produced information that refineries will sell different grades of gas. Some with detergents blended into them and some that don't have detergents. Years ago I worked for a regional convenience store and I was well aware that our gas came from the Phillips 66 refineries. What I hadn't thought about is that refineries could sell different levels of the same product.

[wandering gnome Senior Member Find all posts View Profile Close wandering gnome]

Doug I would be interested in the list of Gas stations you mechanic recommended. I also live in Wichita. If you would like you could email me the list.

[deede Senior Member Find all posts View Profile Close deede]

use of premium only?

This topic was discussed recently on one of our tv station (and, we all know that whatever is revealed on tv is absolutely correct).

The announcer claimed to have checked with Triple A and API.

Anyway, it was reported to be okay to fill up with the lesser grade of petro every 3 fillups (or more if you are comfortable doing so)

The logic used is quite simple (to me):
there are lots of gas station pumps with only one nozzle:

If someone before you used regular gas, there is bound to be some of that grade left in the nozzle/hose when you began using the nozzle -- even though you pressed for the premium.

Therefore, you already have been using the lesser grade without any problem.

At all stations -- including the stations with more than one pump/nozzle at each fillup point:

When a gas companies' trucks fill up the in-ground tanks for the gas station, they also pump from one nozzle, and gas gets mixed together in the ground. (There is no separate nozzle/hose on the trucks for each grade of petro.)

btw., I am using my terms for those thingies that pump gas, and the hoses that hold the gas as it flows from the gas stations' tank to your car. However, I hope you get the gist of what was reported during one of the newscasts here.

[SDSunshine Member Find all posts View Profile Close SDSunshine]

Thanks guys. I went with the medium grade today at fill up and driving home sounded and felt the same as when I filled it with premium. My car runs REALLY well right now (even better than when it was new) and I am pretty religious about the upkeep so I treat it well. I test drove the new GS300 last year and it was actually more sluggish than my current car. So I am sticking with it despite the love dents.

Anyway, I will probably alternate Super and the medium (89) for a while. That should keep it happy.

Katherine

[dougp26364 Senior Member Find all posts View Profile Close dougp26364]

Doug I would be interested in the list of Gas stations you mechanic recommended. I also live in Wichita. If you would like you could email me the list.

I'm not sure I can find it. The only two I can remember are Quiktrip and Phillips 66. I've been buying my gas from Quiktrip since the dealer got my gas gauge working correctly again and I haven't had any problems. I'm sure any GM dealership would be happy to give you a copy of their "approved" gasoline vendors list.

[dougp26364 Senior Member Find all posts View Profile Close dougp26364]

This topic was discussed recently on one of our tv station (and, we all know that whatever is revealed on tv is absolutely correct).

The announcer claimed to have checked with Triple A and API.

Anyway, it was reported to be okay to fill up with the lesser grade of petro every 3 fillups (or more if you are comfortable doing so)

The logic used is quite simple (to me):
there are lots of gas station pumps with only one nozzle:

If someone before you used regular gas, there is bound to be some of that grade left in the nozzle/hose when you began using the nozzle -- even though you pressed for the premium.

Therefore, you already have been using the lesser grade without any problem.

At all stations -- including the stations with more than one pump/nozzle at each fillup point:

When a gas companies' trucks fill up the in-ground tanks for the gas station, they also pump from one nozzle, and gas gets mixed together in the ground. (There is no separate nozzle/hose on the trucks for each grade of petro.)

btw., I am using my terms for those thingies that pump gas, and the hoses that hold the gas as it flows from the gas stations' tank to your car. However, I hope you get the gist of what was reported during one of the newscasts here.

Pretty weak logic when you consider the ratio of lower grade to higher grade when filling up your tank or, when the tanker trucks fill up the underground tanks. Heck, when you get right down to it, every underground tank has some degree of water in the tank as well. It's just that gas is lighter and the pump is not at the very bottom of the tank. Otherwise people would get a tank full of water on occasion.

When I worked for Quiktrip several years ago, the tanks finally got enough water in them that they were literally pumping water instead of gas (there was a design flaw that allowed surface water to get in when the tanker filled them when it was raining). We had put bags over the handles and put out of order signs on all the pumps. As luck would have it, some guy comes in to pay for the tank of "gas" he just filled his car up with. He announced there wasn't anything wrong with the pumps. He'd taken one of the bags off the handle and it worked just fine. Needless to say he didn't make it very far down the road.

I use to test the tanks regularly with a stick. There was a substance that detected water and you could measure for the presence of water and how much there was in each tank. At a certain point something had to be done.

If you don't think they occasionally screw up and put the wrong grade in the tank then you'd be mistaken also. I've seen that happen more than a couple of times. Most of the times it was a higher grade being put into the lower grade tanks.