restartbutton

Last night I stopped to fill up my gas tank. Out of habit, I clicked the button for regular 87 octane gas ( I drive a old truck as my daily) and didn't notice until about 5 gallons went in. I noticed my mistake and switched over to premium 93 octane to finish filling up the tank. I then thru in a Lucas high Mileage injection cleaner hopping that would help "buff up" the gas.

So how bad did I F up, seeing how now I have mixed gas, that's gotta be better than a full tank of regular.

MBCO

You will be fine, these engines run on regular just fine thanks to effective fuel control systems. I use high octane but my friend with same car only uses regular, and has never had issues in 150k miles. The owners manual has a piece on fuels and says you can use regular if premium gas is not available.
Dont worry about it.

KingsoverQueens

I've been using "regular" gas easily for the last 100,000 miles, if not more, with no issues.

BOTUS

87 is low octane, are u at altitude?

as I wrote the other day ROW uses a RON octane numbering system - USA use AKI which means the same octane fuel displays on a USA pump showing 4 wotsits lower - between sea level and 1000 foot, being a European car that was meant to run 95 regular unleaded, in USA that would be 91

I therefore guess u live between 1500 and 3500 foot - where less atmospheric pressure means they generally drop down the Octane numbers to give fuel that burns faster because you are effectively running a low compression engine due to the altitude - of course that all goes out the window when a turbo recovers the lost pressure and you go back to normal seal level fuels

all that background info is likely pretty irrelevant as your baby USA gallons means not much was the wrong grade and you then you mixed high octane at a much greater ratio - the combo sounds like its still higher than the expected rating

octane slows down the speed at which the fuel burns, but also increases combustion temps - so for every use you want the optimal octane rating to get the highest performance possible - running above std may well feel smoother, but its usually costing more money for lower performance and increased consumption and the slower burn and high temps puts more stress on the exhaust valves - however lazy driving, nasty quality, arduous operating conditions etc. means a higher Octane rating is better than one that's too low... the na v8 from 2006 is only supposed to take regular unleaded - high octane makes no difference as its engine management / state of tune doesn't know what to do with high octane - the v12 is a different beast

wildta

If you want to be safe and avoid engine knocking, don't drive it up a mountain and don't push it hard. But like the other poster said, it'll be fine.

BenzV12

Besides unless you have a tuned engine it should make ho harm to the engine at all . Glad, you noticed it though

nath_h

I've always used premium, but it sounds like I'm wasting $20 per tank. I don't push the car hard, and there are no mountain passes on my trip to Target and back. I think I'll try regular next time.

BOTUS

alongside the extra octane - high-end brand, higher cost, premium fuels have a better mix of additives and detergents (and in the UK a lower ethanol %), so they have other benefits which are a good idea

every other fill posh / std / posh / std is a good middle ground for vehicles where the user manual clearly doesn't state use High octane or expect reduced performance and increased consumption when using regular octane fuels

JohnLane

Modern engine management is forever monitoring for ‘Ping’ or ‘Spark knock’ via knock sensors and monitoring how in cylinder events are going via magic monitoring by keeping the arc across the spark plug after the big spark to light the mixture. MAP (manifold absolute pressure) or Air mass meters help engine management know how much air is being ingested and/or pressure in intake manifold. Coolant temp and intake air temp sensors modify maps in the control unit as it needs more fuel when cold. Those of us with direct injection get fuel delivered in the cylinder; timed (in theory) to make it less likely to ping. Oxygen sensors monitor air fuel ratios after the fuel has burned to keep the engine running in the programmer’s vision of ideal.

When everything works as designed with reasonable quality fuel it won’t ping on the urine offered as ‘Regular’ here in the states. Most of the time. If there is a lot of ethanol in it (I have measured as high as 30%) all manner of drivability hell happens when engine management gets lost with what sensors pick up and it tries to correct for it. Mostly Ethanol makes it run lean and makes less power with crap fuel economy as there is less energy in it.

Using a high octane fuel with a good additive package as you get from big brand fuels keeps them running best with happy injectors and less deposits left in the engine. That said.... those of you with direct injection will still end up with all the carbon on the back side of the intake valves that occludes air flow into the cylinder. When a direct injector fails too often they fail to a constant stream of fuel for white smoke out the tailpipe with a dead miss and/or a hydro-locked engine as a cylinder ends up filled with fuel. It happens. Bent connecting rods are a recipe for engine replacement. Port injected engines don’t seem to have this failure. Yet another reason why I see myself driving 279 powered cars for many years.

wildta

Also, summer blend is different than winter blend and should be more forgiving.

JohnLane

When we lived in Washington State the ‘Winter blend’ would boil in the fuel rails for vapor in them in my 221 S65. Hot starts too often made for extended crank time with it starting with a ‘blub-bulb-bbbb-blub’ and stalled. Repeat twice for liquid fuel to get to fuel rail and she would run great until allowed to hot soak again. Annoying! I have seen cars advertised for sale that were ‘Manufactuer Buy Back’ for this issue.

Here in Arizona we only ever get ‘Summer blend’ as the 221 S65 never did that. The 222 car has always started up perfectly regardless of temperature.

wildta

One more thing, on my old Lexus I used regular gas for around 70k miles and started getting engine knock, so I switched to premium (manual states premium only). Never had any engine issues 55k miles using premium afterwards. I was attuned to the knock sound and caught it immediately (was going up a steep grade hill) so I went straight to the pump and topped it off with premium to avoid any potential crankshaft damage. This knock did occur on winter blend but I figured I had saved enough money burning thru 70k miles on regular that it would be best to switch to premium for the remainder of ownership. So if you plan to try regular gas to save some $ at the pump, make sure you can recognize the engine knocking sound if it occurs. Plenty of YouTube videos telling you what sound to look for.

Arrie

You will see drop in fuel mileage and power output while you drive. No other ill effects from it.

BOTUS

if he has the V12.... but his signature says 550 - so in theory should see an improvement in performance and decrease in consumption - as back closer to optimal fueling - rather than putting in slower burning higher than std octane fuels (altitude fun considered....)

Arrie

I dont follow your theory here at all…

BOTUS

high octane fuel ignites later at a higher temp and burns slower - so unless the octane is the exact match to the state of tune the engine was designed to use, high octane fuel produces less go. Yes it can feel happier, often its smoother, but with less performance (not because the energy of the fuel is less - it's much the same), but because of when and how it burns

the v8 only takes normal unleaded, the manual makes no mention of using >91 or >95 ROW numbering system

your words and thinking apply 100% on the v12, or any vehicle where the handbook specifically states it should use super unleaded

an interesting aside - I only read yesterday - high octane often means exhaust valve temps at the end of the burn are higher, and it can lead to increased valve burn out (which is not something anyone ever wants), I guess the take out of that - is the right fuel in the right engine, "hopefully" uses the energy to push the piston down at the optimal rate. And its not left wasted to instead burn the exhaust valves out, because an owner thinks its better fuel...

which it turns out (not so intriguingly as I thought), explains why a vehicle that was meant to run 95 ethanol free unleaded - but now gets ethanol infected trash petrol, perks up a lot when a low ethanol 97 goes in there and you calm down the funny burn with Dipetane as it drops the combustion temps and magically those lower temps also bring down the dangerous emissions you get, but don't want from high combustion temps https://dipetane.com/


.

BOTUS

here's another exciting point - cars and food to eat, all wrapped up in your death...

from seed to make one litre of rot the metal ethanol... it takes 6600kcal of energy, prepping the farmland (you needed for food), putting the crops in, getting them harvested and converted to rubbish - this now magically gives only 5100kcal of energy to stutter down the road with = its not to save the planet !!!!

Arrie

I must say all race car builders and users must be stupid to use high octane (100+) fuels in their cars.

You have an important point wrong in your expert explanation. The high octane fuel does not burn any slower than low octane fuel. High octane allows higher compression in the cylinder without pre-detonation (knocking), i.e., it can be compressed to higher temperature and pressure for more kick on the piston when it is lit by the spark.

JohnLane

Splitting hairs RE amount of power made by lower octane VS high octane for standard engines with standard state of tune guys. Rate of burn for normal combustion is so close as to be a big nothing.

Those of of us with a very high static compression ratio for naturally aspirated or force fed engines designed to get every last bit of power (in particular those with antiquated engine management) will see an easily measured improvement with high octane fuel. Though the difference between 87 and 91 octane isn’t going to get you there. For instance.... the rallycar was turbocharged and programmed for 100 octane. Even with knock sensing running on 91 octane it would rattle. That happened once when we almost ran out of fuel and had to make it back to service.

BOTUS

if you go back and check - I said you should have the optimal octane rating for the state of tune - of course higher octane allows you to up the compression ratio and better optimise the spark

one of my bikes was designed to use 98 or higher the difference on that one is massive - but others meant to run 95 ethanol free is horrible on 99, but works great on ethanol free 97 plus some of that dipetane

JohnLane

We can agree there is not a thing positive about mixing ethanol into our fuels. Doing so is a give-away to the farmers growing corn.... not that they are getting rich doing so.

Arrie

Ethanol is the cheapest ingredient for controlling the octane rating of the fuel. I think the big oil industry is behind this more than anybody realize.