Premium Gas Only

[newlexman]

Hey everyone,

I just wanted some advise on if i can use a grade of gas less than premium and how would it affect my 91 lexus ls 400 with 140000.

Thanks

[90LS400Lexus]

I have often wondered the same thing. When I had my old 1990 LS400, there was one time I almost put in regular without thinking and later wondered what would happen. I just guess it would not run as smoothly and over time, may have mechanical issues? I am not sure. Maybe someone else will know more.

I have a 1972 Chevrolet Caprice Estate wagon and a 1973 Pontiac Grand Ville (both with large V8 engines) and believe it or not, both of them are supposed to have premium (91 octane or higher) fuel, but I have always used regular unleaded with no ill effects.

[Sanpete]

In theory, at least, using lower octane fuel will reduce your engine's performance a little, so that you end up getting poorer gas mileage and paying more than you would per mile buying premium. It shouldn't hurt your engine; the computer should adjust to it to prevent that (it's that adjustment that costs you money in fuel economy). Not sure it always works that way in practice.

There's also the matter of gasoline detergents. Premium grade often has more of them, better for your car.

[Jerry Bransford]

Contrary to popular belief. Premium fuel RARELY has more detergents, fuel injector cleaning additives, etc. than standard 87 octane fuels do so that's no reason by itself to run Premium. Some gasoline manufacturers want you to believe that but it's not usually the case.

That said, the LS400's engine timing is set for Premium but if you run a lower octane which will produce knock/ping, the knock sensor will !Removed! the timing enough to stop the knock/ping which of course also reduces performance. Whether that affects fuel economy is more a matter of how you drive rather than the lower octane itself. :)

[GKLCPA]

I've always run premium in my LS.

I have a Maxima that recommends premium but I've always used regular and had no ill effects as far as I can tell.

When you refer to "performance", what exactly do you mean? Acceleration?

Contrary to popular belief. Premium fuel RARELY has more detergents, fuel injector cleaning additives, etc. than standard 87 octane fuels do so that's no reason by itself to run Premium. Some gasoline manufacturers want you to believe that but it's not usually the case.

That said, the LS400's engine timing is set for Premium but if you run a lower octane which will produce knock/ping, the knock sensor will !Removed! the timing enough to stop the knock/ping which of course also reduces performance. Whether that affects fuel economy is more a matter of how you drive rather than the lower octane itself. :)

[theoldpaths]

Has anyone actually "tested" the theory that running on regular unleaded cuts your fuel mileage?

[tofu]

Some people says that they would run with regular gas, I tried with Plus 89 grade and the CEL came on so I don't even try anymore. Stick with Premium gas.

[Jerry Bransford]

Some people says that they would run with regular gas, I tried with Plus 89 grade and the CEL came on so I don't even try anymore. Stick with Premium gas.

I run Premium, at least 89 but usually 91... but there is no technical reason the CEL light should come on with 89 octane. :)

[charlesranderson]

Has anyone actually "tested" the theory that running on regular unleaded cuts your fuel mileage?

The first three weeks of ownership, I did run regular gas in my 91 LS 400. Mileage varied, but averaged 20, with a low of 18.5 in one tank and a high of 22.5 in another. For the last three weeks I have run premium 93 octane, always a top tier gasoline. Not much change in mileage, but I can tell that the acceleration is smoother--I feel more power in the engine, although I do not often test that. Just had a road trip and got 23 mpg on the highway yesterday--no road trips on regular gas.

For my money, I like the premium, and particularly the top tier with the detergents and cleaners.

[monolex]

Has anyone actually "tested" the theory that running on regular unleaded cuts your fuel mileage?

In my LS400 98 running on regular gives me 1 mile per gallon LESS of mileage.

Tested 700 miles on Premium against 600 miles on Regular

[GKLCPA]

I think I'm going to test my car in similar fashion. The mpg range that you're getting is what I'm getting now with premium. Again, a Maxima is no Lexus, but although it recommended premium, I always ran regular with no ill effects at all. I did that for the entire seven years I've had the car and it has 183K on it and still running strong. Premium costs about 25 cents more a gallon however, which means that you only are spending $ 3 to $5 extra to burn it, so a part of me also says forget about it and just use the recommended fuel.

Has anyone actually "tested" the theory that running on regular unleaded cuts your fuel mileage?

The first three weeks of ownership, I did run regular gas in my 91 LS 400. Mileage varied, but averaged 20, with a low of 18.5 in one tank and a high of 22.5 in another. For the last three weeks I have run premium 93 octane, always a top tier gasoline. Not much change in mileage, but I can tell that the acceleration is smoother--I feel more power in the engine, although I do not often test that. Just had a road trip and got 23 mpg on the highway yesterday--no road trips on regular gas.

For my money, I like the premium, and particularly the top tier with the detergents and cleaners.

[NewGuy19]

I started wondering this myself this morning while filling my car up with premium. It's $3.59 a gallon for premium and $3.09 for 87 and 89 up here. I always run premium but do remember a mechanic telling me awhile back that 89 octane gas now days is better than premium gas ever was back when they built the motor. He was talking about boat motors at the time, but they seem to be even more temperamental when it comes to gas than any car I've ever seen. I've been running 89 in that motor for 3 years now and its run just as good as it ever did with super premium marine gas (93 octane). I don’t think I’m going to switch unless someone can come up with some rock solid evidence to back that up. But it’s something to think about I guess.

[tofu]

Some people says that they would run with regular gas, I tried with Plus 89 grade and the CEL came on so I don't even try anymore. Stick with Premium gas.

I run Premium, at least 89 but usually 91... but there is no technical reason the CEL light should come on with 89 octane. :)

Well I don't know what to say but the CEL did on my 95 LS400 a day later after I put 89 octane grade gas in my tank. I could have bad plugs but as long I use premium CEL never comes on.

[theoldpaths]

Has anyone actually "tested" the theory that running on regular unleaded cuts your fuel mileage?

In my LS400 98 running on regular gives me 1 mile per gallon LESS of mileage.

Tested 700 miles on Premium against 600 miles on Regular

Based on what you say then:

Premium - 20 gal x $3.40 = $68

Regular - 20 gal x $3.00 = $60

Premium - 460 miles @ 23mpg

Regular - 440 miles @ 22mpg

(based on 1 mpg less using regular)

Premium - $68 / 460 = 15 cents per mile

Regular - $60 / 440 = 14 cents per mile

Hmmm... I think I will stick with Premium for the money.

[blake918]

Has anyone actually "tested" the theory that running on regular unleaded cuts your fuel mileage?

I have, and the regular fuel gave me lower fuel economy ( I think it was 2-3 mpg less, I don't remember the exact number.). I worked out the numbers and I would have infact saved money by going with premium in the first place. I think of it as pay me now or pay me later.

[rwallican]

This is a highly debated argument. I've had my 96 for going on 5 years now and have alternated.....a couple tanks of premium and a couple of regular. I do notice more power with the premium but sometimes I feel cheap and just wanna save a few dollars. My mechanic cleaned the throttle body at 120k and commented on how clean it was. I'll continue my method.

[IS400]

1990 LS400 with 225,000 miles plus. I've always run regular 87 octane. No problems. The difference in driving style and conditions do not warrant the cost during city driving. (Mine) If I were to take it on a highway trip I might used premium, but probably not, since I'd be at cruising rpms the entire time in overdrive.

High octane was needed before computer management IMO. I spent 20 years tuning my carbs for spring and winter driving. The lexus does that all on its own.

[rwallican]

Have you had your 90 ls for all 225,000 miles? A salesman at the dealership has a 95 and he told me he never put premium in it and has been running it for over 200k miles. These cars are tanks!

[GKLCPA]

This is what I'm coming up with. There's very little incremental cost to run premium. Actually, this analysis has a wider spread between regular and premium than that in my local area. Premium goes for about 20-25 cents more than regular here in eastern PA when means that I'm paying only $ 3 to $ 4 extra per fill up. On the high side, that's only about $200 extra per year in fuel costs. It's not the incremental cost of premium that's the problem so much as $ 100 a barrel oil. Just 4 years ago, I was paying less than 2 a gallon. That's the day I want to see come back.

Has anyone actually "tested" the theory that running on regular unleaded cuts your fuel mileage?

In my LS400 98 running on regular gives me 1 mile per gallon LESS of mileage.

Tested 700 miles on Premium against 600 miles on Regular

Based on what you say then:

Premium - 20 gal x $3.40 = $68

Regular - 20 gal x $3.00 = $60

Premium - 460 miles @ 23mpg

Regular - 440 miles @ 22mpg

(based on 1 mpg less using regular)

Premium - $68 / 460 = 15 cents per mile

Regular - $60 / 440 = 14 cents per mile

Hmmm... I think I will stick with Premium for the money.

[Kamana]

I started wondering this myself this morning while filling my car up with premium. It's $3.59 a gallon for premium and $3.09 for 87 and 89 up here. I always run premium but do remember a mechanic telling me awhile back that 89 octane gas now days is better than premium gas ever was back when they built the motor. He was talking about boat motors at the time, but they seem to be even more temperamental when it comes to gas than any car I've ever seen. I've been running 89 in that motor for 3 years now and its run just as good as it ever did with super premium marine gas (93 octane). I don’t think I’m going to switch unless someone can come up with some rock solid evidence to back that up. But it’s something to think about I guess.

I switched from 91 (premium) to 87 (regular) and immediately noticed the performance decrease and pinging of the engine. I can live with the performance issue but the pinging is not good. Maybe if I used regular often knocking would have stopped. I then switched to 89 octane, no more pinging and performance is the same as with the higher premium gas. Been using the 89 grade for the past 4 months. Load on the car is always light, no heavy weights in this family. Why pay extra money for fuel if you don't need to.

[Sanpete]

If you're up a couple thousand feet (elevation), 89 octane may work as well for you as 91 would at sea level.

[SRK]

If you're up a couple thousand feet (elevation), 89 octane may work as well for you as 91 would at sea level.

Exactly right! And if you don't use full throttle and just cruise around gently, premium is completely unnecessary as well - no cylinder pressure, no pinging - even at sea level.

[spender]

I only use 94 octane, and it makes my 2004 ls430 more responsive.

[VBdenny]

My guess is that your check engine light came on because you didn't get the gas cap tightened enough. That happens in about any newer car.

[scottmcc]

Keep in mind that the LS is Luxury and Performance. Running premium fuel is recommended because that is how the car was designed for maximum stock performance. Spark Plug Rating, Timing, Etc..

Not running premium will !Removed! performance slightly allowing carbon build up, pinging, etc because lower octances do not burn as hot.

Driving habits will affect your MPG more than the octane you put in your car. Quick Accelleration from stop lights, Getting thrown back in your seat as that passing gear kicks in on the highway as you pass someone who is going to slow on that two lane highway, etc.

I guess its like having a Corvette or Viper and asking if you can run regular fuel..

Using the lower octane will make you push harder on your pedal because you will be thinking, where in the heck is my LS power that I am used to..LOL

I for one love the power from my LS and would not sacrifce that by putting in lower grade or octane fuel. Some states put Ethanol as an additive (Colorado for one) which has rumoured to dry out gaskets and other rubber engine components, so I try to stay away from the Ethanol products.