Home Forums Hunting & Shooting Hunter's Campfire Premium gasoline vs. Mid-grade unleaded

The manual for our Lexus LX470 recommends premium gas and that's what we've always used but it's SO expensive I've considered switching to the mid-grade. Anyone know the reason(s) behind using premium vs. mid-grade unleaded and why it would be specifically recommended in the Owner's Manual? I want to take care of this vehicle (2002 w/ 106k miles) and have been hesitant to switch since but am not sure the benefits of premium gas will outweigh the cost (~$5-$7/fill/week).....

I get better millage with the mid grade than with the lower grade.
Tried the premium and could not tell any difference.

If the compression ratio and ignition advance curve are optimized for higher octane fuel, then that's what the engine wants.

I don't know when engine management systems started to incorporate knock sensors so the computer can back off the timing. Cars thus equipped will run on lower octane fuels, the system protecting them from "knock", but the performance will be compromised, particularly under heavier load like passing, hill climbing and the like.

What that tells us is the particular engine combination needs no more octane than provided by mid grade fuel to perform at its peak.

In my base model tin can there's no advantage to going above the 87 octane base grade unleaded.

High compression engine with regular, or midgrade may knock. Usually the question is why burn premium in regular engines. With the computer timing the engine may adapt to whatever octane, but it may come at a mileage reduction from retarding the engine.

Colorado, in their wisdom has 85 octane, claiming it is equal to 87 at high altitude; I am not sure. What does Nebraska have? I know Wyoming gas is superior to Colorados.

I'm in your same class of vehicle with a bit more. Owners Manual calls for premium and I do it.

Noticed yesterday I received 20mpg on a 500 mile trip using 93oct. The last time I used 91oct I only received 18mpg.

Further, if I can I stay away from the ethanol stuff things just feel better. That's also why I drink good whisky!!

I had a 1987 model car with a small, high compression engine. Double overhead cams, fuel injection, rpm's like crazy. It needed good gas, and it's engine management system wasn't new/sophisticated enough to protect it against low octane fuel. It also had a smallish fuel tank, so while it got nearly 40 mpg highway on cruise control I still had to sometimes buy gas whenever/wherever available.

One time I got caught (out in west Texas IIRC) and the only unleaded available was some horrid 83 (yes, 83) octane motor killer. I put enough in the tank to get me to a bit larger population area and crossed my fingers. Man, did I ever have to feather the throttle to get going without knocking the engine to death. At the first decent place I could stop I dumped two bottles of octane booster in the tank and topped it off with premium.

I dont think you need premium anymore. I could very well be wrong. With E10 all over you have high octane in regular gas. Ethanol is 116 octane. E 10 should raise it at least one octane. I could very well be wrong however but I always wondered if E10 makes midgrade premium grade.

All the addition of ethanol does is allow a lower grade gas be used in the blend for 87, 89, 91 or whatever.

So no, 89 octane with ethanol in it isn't the same as 91 without.

We're pretty much 87 Octane w/ premium running 91 to 93 depending....

Altitude does affect it. Here at 4600+ feet in northern Utah, regular grade is 85. Down south in St George's 2800-foot altitude, regular is rated at 87. I'm assured it is the exact same gas.

One trick you can do is alternate grades. Refill when the tank is at half, and buy mid-grade now and premium next time. It'll save you a few bucks. Not much, but it won't harm your mileage or engine much, either.

Octane rating once was way more important than it is with currently manufactured gas engines - octane rating now seems to be a gimmick taking advantage of those who don't understand the issues. In my limited view, the stuff labeled "premium" should be that with no ethanol added - that stuff can be a mess.

The primary mechanical/chemical issue to be dealt with is pre-ignition (fuel starts to burn too soon before the piston reaches TDC) and this is where the "knocking" arrives. That is mechanical hammering on a small scale, but it will cause wear and damage over time. Seems like almost all modern computer-controlled engines - especially those with variable mechanical aspects - will easily control timing of fuel ignition as related to power output and mpg.

So - how important is high octane today for the average owner? Don't know, but am suspicious that those "premium" labels and charges don't relate to higher octane as in the past. Maybe something in there is worth the higher cost, but am thinking it is not octane-related ignition control. Am thinking that some of those premium fuel mixes might have a higher energy quotient - thus giving better mpg in general - but have no evidence there.

In older engines with owner-adjusted mechanical ignition systems, especially those built with high compression ratios - octane control can be a real factor. Do you remember tetraethyl lead (ICC)? Wish I had a gallon (careful - very poisonous).

However, with precise addition of aromatics, particularly like toluene (the perfect gasoline), one can boost octane rating in non-ethanol gas to help in such cases. But, unless you are craving big power, easier to de-tune.

A friend of mine drives a high performance car with direct injection, high compression, and supercharging. Sure, the controller will protect the engine, but it detunes it to do so.

You can buy 110 at some of the pumps in SC. Especially, around the local Friday and Saturday night tracks.

Wish we had such near here - no such luck. When I worked at Sunoco in the 1950s, in R&D we were running quality control tests on that new blend pump - it enabled the consumer to select one of about 7 octane ratings from the same pump. It selectively blended a base gas with a high octane concentrate. Their label range started at 190 (not octane rating) and the top lever was Sun 260. That might still be what they are selling near those race tracks.

Back then we built up more than one engine that needed the 260. Good old days.

The book for the old 944A Cat loader says to use the cheapest fuel that gives satisfactory performance. Now that is diesel, and it also says to change the crankcase oil oftener if a high surfer fuel is used.

I'd still use the cheapest gas/fuel, that gives satisfactory performance. Check mileage each way, and do the math.

I had a Toyota Sequoia with the same 4.7 liter V8 engine and it required regular unleaded.

Your cars computer is set to run whatever octane rating is stated in the owners manual. Put anything else in the tank and the computer will adjust out the difference. You gain nothing but a higher fuel bill. In the case of the Lexus I would expect performance to suffer as the computer will adjust fuel and spark timing to prevent pre-ignition.

That's correct. Many years ago I worked for an Acura dealership and all cars called for 91 octane. But I sold one to an Air Force pilot, who said he had run the calculations and that 85 octane would work great at altitude and it was unnecessary.

We run 93 octane in my wife's supercharged Audi crossover and her Porsche Boxster as recommended and they run just fine. I run the same in my '73 Cleveland powered Mach 1 and it is fine. My Tundra sees 87 octane and it is fine. All with ethanol. I will leave it at that.