Drop In Gas Mileage

[frodo1028]

I have a 1992 LS-400 with 152,000 miles on it. Lexus did a full tune-up on it and changed plus at 122,000 miles. Now it seems to have a slight hesitation when I step on the accelerator and more importantly, the gas mileage keeps dropping. Several months back, I was getting 19-20 mpg. Over the last several months, this has droped to 18, then 17 and now it isn't getting better than 15 mpg. Does this sound like another tune-up is in order or could it be something in the computer. I have noticed that the exhaust smells really fuel rich.

Any advice would be appreciated.

Thanks,

Frodo

[1990LS400]

A tune-up on a gen 1 LS400 is certainly good for a lot more than 30K miles. IMO, doing a tune-up more often than recommended is a waste of money. But if you are smelling gas, there could well be something wrong and you might want to take it in for an evaluation.

Have you had your LS for a number of years? If so, is your mileage this summer different from past summers or are you paying more attention because gas prices are so high?

Over the 16 years I've been driving LS400's, I've noticed that there can be a huge difference (well over 10 mpg) in gas mileage depending on what time of year it is, ratio of highway to city driving, how many people and how much luggage I am carrying, wind direction during highway driving, etc. I've kept track of every single gallon of gas (or diesel) I've used for 40 years, so I'm not just "blowing smoke".

15 mpg during a hot August in mixed city/highway driving with the A/C on is in line with what I experienced on a gen 1 LS400.

[LRP_LS400]

i agree with the above statement

[Threadcutter]

I have a 1992 LS-400 with 152,000 miles on it. Lexus did a full tune-up on it and changed plus at 122,000 miles. Now it seems to have a slight hesitation when I step on the accelerator and more importantly, the gas mileage keeps dropping. Several months back, I was getting 19-20 mpg. Over the last several months, this has droped to 18, then 17 and now it isn't getting better than 15 mpg. Does this sound like another tune-up is in order or could it be something in the computer. I have noticed that the exhaust smells really fuel rich.

Any advice would be appreciated.

Thanks,

Frodo

Frodo:

I was getting 19-20 mpg. Over the last several months, this has droped to 18, then 17 and now it isn't getting better than 15 mpg.

With all due respect to everyone, I don't agree that that is normal/seasonal. That is a 25% reduction in mileage. There's something wrong. Probably releatively simple to fix, but in need of repair nevertheless.

I would have a good (ie; Trustworthy) Independant mechanic look at the throttle body & determine if it needs cleaning. Inspection is easy/cheap. Also have him pull a fuel injector & recommend whether or not the injectors need a bath.

Have you ever done the "SeaFoam" treatment?. Do a searchon this site for SeaFoam.....there's plenty of info.

[Broker]

Have you ever done the "SeaFoam" treatment?. Do a searchon this site for SeaFoam.....there's plenty of info.

I highly recommend this as well. I've seen it do wonders on some engines.

[Ross W.]

I have noticed that the exhaust smells really fuel rich.

Any advice would be appreciated.

Thanks,

Frodo

A stinky exhaust would be a red flag for me. Do as the others have suggested, i.e the Sea Foam treatment, check the sparkplugs, etc. but definitely get it to a mechanic and scan for codes, and to hook it up to a sniffer to see how badly off the fuel mixture is. The worst average I've had recently, with the heatwave, was 18 mpg. Mostly in mixed driving I've been seeing 23-24 mpg consitently.

HTH!

[AustinGT]

Wow- 23-24 is really good. I would add that, like 1990LS400, my gas mileage varies a lot as well. In mostly around town driving, with the a/c on, I usually get between 16 and 17 mpg (using 91 octane). However, on a recent trip to Fresno, I got 25.5 mpg with the a/c on all the way and the cruise set at 75+. I would add that I am not an extremely aggressive driver, but I do enjoy that V8 when possible!

[OmarG]

I have seen as good as 24 with fast hwy driving. I am aggressive but safe and polite. That might sound like an oxymoron but i always let people in if they are polite. Anyways in city urban driving i see about 18? not too bad with my lead foot. I am thinking of doing seafoam on my first oil change. Is wal-mart that bad? 25 bucks for an oilchange seems good to me! Ah btw in a month and a half i have put 3300 miles on my car. Crazy miles for a teen huh? Sometimes i'm bipolar with the gas. I might turn off the ac and ease along and try to hear the whispering engine... and a minute later turn on ETC and power off a ramp. I should get a smaller car to thrash around. Sorry.. i babble.

[1990LS400]

I have seen as good as 24 with fast hwy driving. I am aggressive but safe and polite. That might sound like an oxymoron but i always let people in if they are polite. Anyways in city urban driving i see about 18? not too bad with my lead foot. I am thinking of doing seafoam on my first oil change. Is wal-mart that bad? 25 bucks for an oilchange seems good to me! Ah btw in a month and a half i have put 3300 miles on my car. Crazy miles for a teen huh? Sometimes i'm bipolar with the gas. I might turn off the ac and ease along and try to hear the whispering engine... and a minute later turn on ETC and power off a ramp. I should get a smaller car to thrash around. Sorry.. i babble.

Yes, Wal-Mart is "that bad" and so are the quicky oil change places. The easiest way to avoid damage and other grief is to do oil changes yourself. 24 mpg is wonderful for "fast hwy driving" -- far better than I generally got -- and I drove with a light foot. The best mileage I saw in 183,000 miles of driving in my gen one, 3 speed+overdrive 4th transmission LS400 was only slightly over 24 mpg -- and that was with a fairly strong tail wind.

[VBdenny]

Our averages between 17mpg in city driving to around 24 on the highway. Adjustments to the accelarator will significantly alter fuel consumption rates.

[frodo1028]

With all due respect to everyone, I don't agree that that is normal/seasonal. That is a 25% reduction in mileage. There's something wrong. Probably releatively simple to fix, but in need of repair nevertheless.

I would have a good (ie; Trustworthy) Independant mechanic look at the throttle body & determine if it needs cleaning. Inspection is easy/cheap. Also have him pull a fuel injector & recommend whether or not the injectors need a bath.

Have you ever done the "SeaFoam" treatment?. Do a searchon this site for SeaFoam.....there's plenty of info.

Thanks for the advice on the Seafoam! I had never heard of it but it definitely looks like it is worth trying. I am becoming a believer in these additives. I tried the engine oil stop leak by Barr's and it worked wonders. I even made a post on this forum to that effect. I will try the SeaFoam and let you know.

Thanks again,

Frodo

[VBdenny]

how much does the stuff cost?

[frodo1028]

I did a search on Seafoam and they say it is about $5/can. There is also a lot of differing opinions on whether or not to use it in the oil but most people agree that it is good for the gasoline.

[desires a lex]

I read somewhere in the manual that using one of the odometer display buttons, you can see what your gas mileage is, is that true? If so, how do I do it? I have a 96 ls

[frodo1028]

Thanks for the advice on the Seafoam! I had never heard of it but it definitely looks like it is worth trying. I am becoming a believer in these additives. I tried the engine oil stop leak by Barr's and it worked wonders. I even made a post on this forum to that effect. I will try the SeaFoam and let you know.

Thanks again,

Frodo

Hey Threadcutter. I tried the Seafoam and am VERY happy to say that it worked wonders. I put one can into the gas tank and I also did the trick of sucking up 1/2 of another can through the vacuum line for the power brake booster. It smoked like crazy for a good 5 minutes but I am happy to say that the gas mileage is back up to 18.8 mpg instead of the 14.7 mpg that I was down to. That is 4 mpg improvement! Awesome!

Thanks for the teriffic advice.

Frodo

[Threadcutter]

Hey Threadcutter. I tried the Seafoam and am VERY happy to say that it worked wonders. I put one can into the gas tank and I also did the trick of sucking up 1/2 of another can through the vacuum line for the power brake booster. It smoked like crazy for a good 5 minutes but I am happy to say that the gas mileage is back up to 18.8 mpg instead of the 14.7 mpg that I was down to. That is 4 mpg improvement! Awesome!

Thanks for the teriffic advice.

Frodo

Frodo:

That's very cool news! :D

Thanks for the teriffic advice.

You're quite welcome, but I was just passing on what was passed on to me by others. When given the opportunity, please do the same. Thanks

BTW, resist the urge to get the inside of your engine squeaky clean by continually sucking up 1/2 of a can through the vacuum line. Doing it too often can/probably will damage seals and/or gaskets .

I do mine about every 7 to 10,000 miles. Also, I use about 1/3rd of a can because I'm concerned about "hydro-locking" the engine. This occurs when too much of the liquid SeaFoam gets into one cylinder. As you know, fluids won't compress, so when the piston comes up and tries to compress the SeaFoam, it's like a "brick wall" for the piston, which is a bad thing.

As a point of reference; My '95 gets 23 to 24.5 mpg in the city & 25.5 to 27 hiway. That's why your numbers were throwing me off. I've got a '96 ES300 (love it too.....) & it gets 29 hiway.