1994 LS 400: how do i improve my gas mileage?
03-23-14, 12:17 PM
#1
Pole Position
Thread Starter
1994 LS 400: how do i improve my gas mileage?
here is what I've done so far......i use 91 octane gas, i replaced the pvc valve and grommet, the tires are oem michelins, i use full synthetic oil, replace air filter, replaced timing belt with water pump & thermostat.....my next plan of action is replacing the plugs and wires, electronic coolant temperature sensor, and fuel filter. What other advice does anyone have for me? i currently get around 17 mpg city driving now........THANKS IN ADVANCE!
03-23-14, 01:00 PM
#2
Use regular, 91 is not needed, that will not get you better mileage, but cheaper full-ups, which is about the same thing. A good gain in fuel mileage can be had by simply changing your driving habits, starting fast, driving fast will have a big effect on mileage.
Not sure what it equals out to, but my high-mile '94 gets about 400km/full tank.
Not sure what it equals out to, but my high-mile '94 gets about 400km/full tank.
03-23-14, 01:22 PM
#3
Lexus Champion
premium fuel (91 and up) gets me approximately 11% better fuel mileage after doing several controlled tests, vs. the only 7% premium I pay for it at Costco over the price of 87, makes it a no-brainer! 
not to mention the increased performance, and cleaner emissions!
it makes sense if you think about it, for the following reasons:
● the ECU has to severely retard the ignition timing and make other performance and mileage-killing adjustments to prevent knocking (aka ping, spark knock, detonation) which can damage your engine - this is what the knock sensors are for, to detect this and let the ECU know it needs to make these sub-optimal adjustments to prevent any damage!
● Toyota Engineering says you should use Premium Fuel Only - believe me, they are under a lot of of pressure to make cost of ownership as low as possible vs. competitors, so they sure wouldn't greatly increase this cost of ownership number by specifying and requiring premium fuel, if it were not absolutely necessary!
not to mention the increased performance, and cleaner emissions!
it makes sense if you think about it, for the following reasons:
● the ECU has to severely retard the ignition timing and make other performance and mileage-killing adjustments to prevent knocking (aka ping, spark knock, detonation) which can damage your engine - this is what the knock sensors are for, to detect this and let the ECU know it needs to make these sub-optimal adjustments to prevent any damage!
● Toyota Engineering says you should use Premium Fuel Only - believe me, they are under a lot of of pressure to make cost of ownership as low as possible vs. competitors, so they sure wouldn't greatly increase this cost of ownership number by specifying and requiring premium fuel, if it were not absolutely necessary!
03-23-14, 01:38 PM
#4
Lexus Champion
as far as getting better mileage, here is what I would do in order of how much difference it will likely make:
● make sure your tires are kept inflated to 32 psi cold, or slightly higher, and if the tires are over 4 years old, replace them for both mileage and safety's sake, time wear tires as much as mileage does!
● replace the engine coolant temperature sensor with the factory OEM one from Sewell Lexus or other online dealership
● replace the thermostat with the factory OEM one from Sewell Lexus or other online dealership
● replace the wires and plugs with genuine NGK or Denso from amazon or rockauto.com
● replace the distributor caps and rotors with the factory OEM ones from Sewell Lexus or other online dealership
● replace the O2 sensors with genuine Denso from rockauto.com or amazon
● get a good 4 wheel alignment
● make sure your tires are kept inflated to 32 psi cold, or slightly higher, and if the tires are over 4 years old, replace them for both mileage and safety's sake, time wear tires as much as mileage does!
● replace the engine coolant temperature sensor with the factory OEM one from Sewell Lexus or other online dealership
● replace the thermostat with the factory OEM one from Sewell Lexus or other online dealership
● replace the wires and plugs with genuine NGK or Denso from amazon or rockauto.com
● replace the distributor caps and rotors with the factory OEM ones from Sewell Lexus or other online dealership
● replace the O2 sensors with genuine Denso from rockauto.com or amazon
● get a good 4 wheel alignment
03-23-14, 01:41 PM
#5
I had been running 87 for about a year and recently switched to Shell 93. The gas mileage seems to be about the same. I normally get around 21.5-22.5 MPG combined. The car does certainly feel like it is running better with the higher octane fuel. I'm going to be running the Shell 93 for a couple months to check the mileage accurately. Not running 91 because it is not readily available in Florida.
17 MPG does not seem bad for these cars if you are doing mostly city driving. According to my window sticker the original ratings were 18 city and 23 highway. The biggest change to fuel economy is going to be in you driving habits and how much city vs highway driving you do. The winter blends the fuel companies have been using also result in lower fuel economy.
17 MPG does not seem bad for these cars if you are doing mostly city driving. According to my window sticker the original ratings were 18 city and 23 highway. The biggest change to fuel economy is going to be in you driving habits and how much city vs highway driving you do. The winter blends the fuel companies have been using also result in lower fuel economy.
03-23-14, 01:43 PM
#6
premium fuel (91 and up) gets me approximately 11% better fuel mileage after doing several controlled tests, vs. the only 7% premium I pay for it at Costco over the price of 87, makes it a no-brainer!
not to mention the increased performance, and cleaner emissions!
it makes sense if you think about it, for the following reasons:
● the ECU has to severely retard the ignition timing and make other performance and mileage-killing adjustments to prevent knocking (aka ping, spark knock, detonation) which can damage your engine - this is what the knock sensors are for, to detect this and let the ECU know it needs to make these sub-optimal adjustments to prevent any damage!
It only has to "severely retard" the ignition timing under extreme load situations, under which you get poor mileage anyway. Under standard driving conditions in the city and especially on the highway, premium vs. regular octane fuel makes no difference to timing. Hence it makes minimal difference to economy, as has been shown multiple times by multiple EPA and research journals. If octane was all that was needed to give better mileage then ethanol by your description would give better mileage than gasoline, only it doesn't, by a huge margin. (due to the huge amount of difference in a gallon of ethanol vs. gasoline.) While your test may have worked under the specific conditions you subjected them to (namely, you driving), that alone doesn't change the actual facts.
● Toyota Engineering says you should use Premium Fuel Only - believe me, they are under a lot of of pressure to make cost of ownership as low as possible vs. competitors, so they sure wouldn't greatly increase this cost of ownership number by specifying and requiring premium fuel, if it were not absolutely necessary!
Luxury car manufacturers are under the most minimal pressure to lower the "cost of ownership", especially for Flagship models. The current IS series still (and has always) had a Premium fuel requirement, purely because it is only at the rated fuel do you get maximum power.
not to mention the increased performance, and cleaner emissions!
it makes sense if you think about it, for the following reasons:
● the ECU has to severely retard the ignition timing and make other performance and mileage-killing adjustments to prevent knocking (aka ping, spark knock, detonation) which can damage your engine - this is what the knock sensors are for, to detect this and let the ECU know it needs to make these sub-optimal adjustments to prevent any damage!
It only has to "severely retard" the ignition timing under extreme load situations, under which you get poor mileage anyway. Under standard driving conditions in the city and especially on the highway, premium vs. regular octane fuel makes no difference to timing. Hence it makes minimal difference to economy, as has been shown multiple times by multiple EPA and research journals. If octane was all that was needed to give better mileage then ethanol by your description would give better mileage than gasoline, only it doesn't, by a huge margin. (due to the huge amount of difference in a gallon of ethanol vs. gasoline.) While your test may have worked under the specific conditions you subjected them to (namely, you driving), that alone doesn't change the actual facts.
● Toyota Engineering says you should use Premium Fuel Only - believe me, they are under a lot of of pressure to make cost of ownership as low as possible vs. competitors, so they sure wouldn't greatly increase this cost of ownership number by specifying and requiring premium fuel, if it were not absolutely necessary!
Luxury car manufacturers are under the most minimal pressure to lower the "cost of ownership", especially for Flagship models. The current IS series still (and has always) had a Premium fuel requirement, purely because it is only at the rated fuel do you get maximum power.
OP-
Better off doing standard maint. before anything else. Wires, plugs, rotors, caps, checking ignitors/coils, cleaning throttle body, confirming TPS setup, and finally CHANGING YOUR DRIVING HABITS will have a profound effect on your observed gas mileage. That being said, 17mpg observed in mostly city driving is quite good for a 1st gen LS.
03-23-14, 01:52 PM
#7
Lexus Champion
I respect your knowledge, but just got to go with the gurus that designed the 1UZ engine on this one!
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03-23-14, 01:59 PM
#8
Lexus Champion
17 MPG does not seem bad for these cars if you are doing mostly city driving.
17mpg observed in mostly city driving is quite good for a 1st gen LS.
03-23-14, 02:07 PM
#9
OP stated the 17 MPG is city driving and the rating for the city mileage is 18 MPG. I have my window sticker in front of me from a '92 that states 18 MPG for city. Of course everybody drives differently which is a major factor in mileage.
03-23-14, 02:08 PM
#10
Disagreement is great! - that is what is so cool about the Internet, free speech! - so disagree all you want, meanwhile, myself, Toyota Engineering, and millions of drivers worldwide will be sticking with Premium Fuel Only on the cars that specify it!
I respect your knowledge, but just got to go with the gurus that designed the 1UZ engine on this one!
I respect your knowledge, but just got to go with the gurus that designed the 1UZ engine on this one!
Considering the '95 LS was rated at 19/25 and was 200+ lbs lighter than the 1st gen, with more power and torque, and the '94 was rated at 18mpg city, i'd say he's doing well. Especially since they were rated with the "old" EPA test cycle which was more inflated than today's in terms of real-world performance.
03-23-14, 02:13 PM
#11
IDK if I would call the EPA test cycle real-world. The average highway speed is 48.3 MPH. http://www.fueleconomy.gov/feg/fe_test_schedules.shtml
If it has been awhile since the plugs, wires, etc. has been done he might see a slight improvement in mileage.
If it has been awhile since the plugs, wires, etc. has been done he might see a slight improvement in mileage.
03-23-14, 02:21 PM
#12
Lexus Champion
Sufficient octane is only one factor in fuel mileage, and ethanol's higher octane is mostly a waste in modern cars, because once you reach the required octane to prevent knock, contrary to popular misconception, higher octane does not buy you additional power or fuel mileage.
Ethanol's lower energy content (76,100 BTUs/Gal.) is a big contributor to its reduced fuel economy compared to gasoline (114,100 BTUs/Gal). Even though FFVs burn E85 (81,800 BTUs/Gal) and the energy penalty isn't as severe, it still requires more fuel to do the same work. On paper, it takes 1.39 gallons of E85 to move a flex-fuel vehicle the same distance as 1 gallon of gasoline.
source
Ethanol requires more heat to atomize (reduce to a fine mist) than does gasoline. In a straight alcohol engine, the fuel delivery system would be designed in such a way that the fuel would be preheated to some degree to assist atomization before delivery to the combustion chamber. Again a compromise must be reached to burn both fuels in a flex engine. This is the main reason for the existence of the E85 blend. The addition of 15 percent gasoline to the 85 percent alcohol overcomes the cold evaporation problems of pure ethanol.
source
So higher than necessary octane is not going to buy your any additional benefit, nor is ethanol and its reduced energy content and other drawbacks.
I am just saying that I have great results with the octane rating fuel specified by the engine designer, I am not saying higher is better, for example, there is no benefit to a 100 octane gas in an LS400 over 91 - the way octane rating works, once you get to a sufficient octane, higher octane is no advantage unless you were to build your LS400 into a racing vehicle - so for example, a NASCAR or Formula 1 car would benefit from higher than 91 octane, but not our cars, unless you made a race car out of an LS
Ethanol's lower energy content (76,100 BTUs/Gal.) is a big contributor to its reduced fuel economy compared to gasoline (114,100 BTUs/Gal). Even though FFVs burn E85 (81,800 BTUs/Gal) and the energy penalty isn't as severe, it still requires more fuel to do the same work. On paper, it takes 1.39 gallons of E85 to move a flex-fuel vehicle the same distance as 1 gallon of gasoline.
source
Ethanol requires more heat to atomize (reduce to a fine mist) than does gasoline. In a straight alcohol engine, the fuel delivery system would be designed in such a way that the fuel would be preheated to some degree to assist atomization before delivery to the combustion chamber. Again a compromise must be reached to burn both fuels in a flex engine. This is the main reason for the existence of the E85 blend. The addition of 15 percent gasoline to the 85 percent alcohol overcomes the cold evaporation problems of pure ethanol.
source
So higher than necessary octane is not going to buy your any additional benefit, nor is ethanol and its reduced energy content and other drawbacks.
I am just saying that I have great results with the octane rating fuel specified by the engine designer, I am not saying higher is better, for example, there is no benefit to a 100 octane gas in an LS400 over 91 - the way octane rating works, once you get to a sufficient octane, higher octane is no advantage unless you were to build your LS400 into a racing vehicle - so for example, a NASCAR or Formula 1 car would benefit from higher than 91 octane, but not our cars, unless you made a race car out of an LS
03-23-14, 02:33 PM
#13
Check-replace those old drying vacuum lines too.
As for fuel, gas mileage those are separate threads.
https://www.clublexus.com/forums/ls4...er-thread.html
https://www.clublexus.com/forums/ls4...er-thread.html
As for fuel, gas mileage those are separate threads.
https://www.clublexus.com/forums/ls4...er-thread.html
https://www.clublexus.com/forums/ls4...er-thread.html
03-23-14, 02:34 PM
#14
Formula one cars run on fuel that is very similar to gas you purchase at the local gas station. Not much special about it. The octane rating for F1 is 87 (RON+MON)/2.
http://www.formula1.com/inside_f1/ru.../8700/fia.html
http://www.formula1.com/inside_f1/ru.../8700/fia.html
03-23-14, 03:01 PM
#15
Lexus Champion
Formula one cars run on fuel that is very similar to gas you purchase at the local gas station. Not much special about it. The octane rating for F1 is 87 (RON+MON)/2.
http://www.formula1.com/inside_f1/ru.../8700/fia.html
http://www.formula1.com/inside_f1/ru.../8700/fia.html
but actually, I said they would benefit from higher octane, and they would, and occasionally teams try to sneak some higher octane in, like Mika Häkkinen and others have, and sometimes they get caught!
Last edited by LScowboyLS; 03-23-14 at 03:05 PM.