Been using premium gas since I bought it, just because its what the truck says it needs. Is it 100% necessary? does anyone use 85% instead of 91%?

Thanks
Mark

 

Unless you like driving around retarded... The computer will sense the pinging and retard the timing. You'll get slightly less mpg. It will work but WTF would do that for when gas is so cheap right now?

I'm happy as hell to have a tank full of $2.89 per gallon Chevron Supreme right now even if there is nowhere to go.

 

There are typically a couple reasons why premium fuel is specified. The higher the octane, the higher the flash point of the fuel, which means high octane, aka premium fuel, resists burning. The goal of this harder-to-burn fuel is to prevent pre-detonation or "pinging". The are primarily two major reasons for pinging. The first is that the engine has a higher compression ratio and without premium fuel the mixture will light off from heat and compression alone, and before the piston is in the optimum position in its stroke which is when the computer will fire the ignition. This is not the case with the Disco. The second reason an engine will require premium fuel is because the computer has intentionally advanced the spark in the timing cycle in an effort to keep temps up (for emissions) and to increase performance. In either case, when you run a lower octane than specified the fuel is combusting when you really don't want it to. In extreme cases the fuel ignites when the piston is still traveling up, and this of course means it has to overcome the force of the explosion to get over the hump and start it's downward travel, which is when it makes its power. It's counter productive to have the fuel ignite and push the piston down when the crankshaft is trying to push it up. It's also really hard on the engine.

Now the good news. These engines have knock sensors on them which detect pinging, and the ECU will adjust the spark in the timing cycle to ensure that the fuel is igniting at the appropriate time. If you're running low octane fuel the ECU will retard the spark which ignites the fuel sooner and ensures a good compression stroke. The downside is that you may see slightly reduced power or economy by running lower octane fuel, however you''re not going to hurt anything by doing so.

 

I don’t think you have to. I think there are a few members on here that have seen engines look like crap with or without running premium fuel.
In Canada we get screwed on premium. It’s roughly 20-30 cents more a litre and a 87 litre is $1.20 a litre on a regular basis. So do the math $1.50 a litre to fill a tank is roughly 120 bucks.

 

Thanks, I was thinking on that today, in Nz it’s worse we have 91 octane as regular, 95 as super and some have 98 octane as well , and if you look hard you can get 100 octane, the price difference is crazy and I’m less sure now lol on what’s best, I’ve been running 91 and 95

 

91 is all that is required, the European's measure octane slightly differently. Anything above is a waste and below may affect fuel economy and mileage. I found higher ethanol content has a bigger effect on my gas mileage

 

New Zealand? Oh man you guys and most of Europe get screwed really bad. That’s why most are diesel.
There is no way most people could afford gas for a disco with the wages in some parts of Europe. Definitely not where I’m from

 

The difference isn’t worth the offsetting disadvantages.

 

I wish that was how the price difference was in my area. It's more like 75 cents to 1.00 more for 93 octane vs 87 octane. In my 95 since she doesn't have knock sensors I run 93 octane. In the GEMS D1, and Bosch D2's I run 87 octane and they do fine. They are not all carbon-ed up inside, they do not roll coal (carbon deposits when I pass someone), but I do let my engines tach up to 4,500 RPM's or sometimes higher. Zero issues and I've got 5 personal D1/D2's combined. If it was an issue I'd have seen something pop up by now. Now do I have the max HP output with lower fuel? No, but I'm also not towing, or racing it. I have no problem buying 93 octane when I find it within a 35 cent difference (Very common in other regions like Austin/San Antonio). However in Houston/SETX it's 75 cents to 1.00 higher.

Bottom line it will not kill your engine, but you will have less HP, and I would either run a good fuel cleaner thru every 3K (should be doing that regardless IMHO), and do not drive it like Mrs Daisy (aka barely letting the engine rev up which causes carbon deposits to collect quickly).

 

I've always used premium, or almost always, but two things are notable about Brandon318's graphic.

First, he shows a 10¢ per gallon differential between regular and premium. Right now, where I live, premium is ~35¢ more than regular. And GasBuddy shows a premium vs. regular differential of more like 40¢ in Monterey, where Brandon318's info says he is.

And second, I'm happy premium isn't now $3.39/gallon where I live. Premium here is now under $1.99/gallon. And even in Monterey GasBuddy shows premium available as low as $2.95/gallon and regular at $2.49.

But back to the point. Even at a 40¢/gallon differential, that's $10 more per fill up, if the tank is completely empty. Maybe not chump change if you're driving your DII a lot, but still a lot less than a lot of the repairs we spend money on for our trucks.

But here's a related question I've wondered about for a long time. Is there a difference between the effects of regular vs. premium on a long road trip at 60-70 mph speeds where the engine is kind of just loafing along, vs. stop-and-go driving where you are constantly accelerating and decelerating? In other words, is it any more okay to use mid-grade or regular when you are heading out on a 300+ mile road trip. I don't know. I hope there are contributors here who have the actual technical knowledge to answer, instead of just speculating. Thanks.