Not Very Good Milage With My Ls400 '94

[Imzjustplayin]

I already posted another thread about how my car is having starting issues but I thought I should create a thread related to this anyways. My fuel tank is now slightly less than half full and I've calculated my future total range of being around 400miles and I wanted to know what I can do to fix my milage issue. When you calculate a total range of around 400 miles, it turns out I'm only getting like 17.7mpg and I was under the impression the car got something like 22mpg. I *think* the tranny fluid needs to be changed, could this be the resulting issue of poor mileage? The tranny was having issues shifting a while back but now it isn't, I'm not sure thats a good thing.. How many quarts of tranny fluid does the LS400 94 need again? What are some things I can check to see if they've gone bad and will hurt my mileage?

[leximus]

I believe they take 8.7 quarts of tranny fluid (8.3 liters). Be sure you go to a Toyota dealer and get the tranny fluid there.

[Imzjustplayin]

I believe they take 8.7 quarts of tranny fluid (8.3 liters). Be sure you go to a Toyota dealer and get the tranny fluid there.

Are you saying my valvoline Maxlife 75,000 mile Dexron III tranny fluid isn't good enough?

http://www.valvoline.com/pages/products/pr...l.asp?product=6

Cause if I remember correctly, ALLDATA said this would be suitable.

[GKLCPA]

My car was recently out of alignment and my average mpg decreased to 18-19 mpg rather than the normal 20-21 mpg. Properly inflated tires and making sure your vehicle is aligned are some simple things to check and correct. These cars seem to be very sensitve to these two issues.

[1990LS400]

When you calculate a total range of around 400 miles, it turns out I'm only getting like 17.7mpg and I was under the impression the car got something like 22mpg.

Have you had your 94 LS long? Are you keeping track of miles per gallon over the long haul to see how the mileage fluctuates in relation to the type of driving?

The gen one LS400 had an EPA rating of 18 mpg city and 23 mpg highway. EPA figures are often very optimistic.

If your 17.7 mpg is in mixed city driving, then that does not seem very far off what you should expect. I drove a similar gen 1 (1990) LS for over nearly 14 years and kept track of every gallon the car used and the mpg on every tank full. I think my best ever mileage on a tank was a little over 24 mpg and that was on a trip where all the miles were on the highway and with a tail wind. With a very gentle foot on the thottle, I averaged between 17 and 20 mpg in mixed city driving which included quite a bit of highway driving.

In city-only driving, my gen 1 LS400 would get 15-16 mpg on a tank which I though was pretty good for a nearly 4000 pound sedan made during those years.

My current 2000 LS400 with its five speed automatic gets substantially better mileage than my 1990 LS400 did - particularly on the highway.

It sounds like your car is operating normally when it comes to gas mileage and I doubt if changing the tranmission fluid is going to do anything to improve it.

If your transmission is having shifting issues, inspect the wiring harness in the left trunk hinge for cracked or broken wires - do a search on this forum for information on how to fix for a couple of bucks by splicing wires. Intermittent shifting problems occur as the wires start to crack and become progessively worse. My gen 1 LS became almost inoperable until I fixed the broken wires in the hinge.

[Imzjustplayin]

When you calculate a total range of around 400 miles, it turns out I'm only getting like 17.7mpg and I was under the impression the car got something like 22mpg.

Have you had your 94 LS long? Are you keeping track of miles per gallon over the long haul to see how the mileage fluctuates in relation to the type of driving?

The gen one LS400 had an EPA rating of 18 mpg city and 23 mpg highway. EPA figures are often very optimistic.

If your 17.7 mpg is in mixed city driving, then that does not seem very far off what you should expect. I drove a similar gen 1 (1990) LS for over nearly 14 years and kept track of every gallon the car used and the mpg on every tank full. I think my best ever mileage on a tank was a little over 24 mpg and that was on a trip where all the miles were on the highway and with a tail wind. With a very gentle foot on the thottle, I averaged between 17 and 20 mpg in mixed city driving which included quite a bit of highway driving.

In city-only driving, my gen 1 LS400 would get 15-16 mpg on a tank which I though was pretty good for a nearly 4000 pound sedan made during those years.

My current 2000 LS400 with its five speed automatic gets substantially better mileage than my 1990 LS400 did - particularly on the highway.

It sounds like your car is operating normally when it comes to gas mileage and I doubt if changing the tranmission fluid is going to do anything to improve it.

If your transmission is having shifting issues, inspect the wiring harness in the left trunk hinge for cracked or broken wires - do a search on this forum for information on how to fix for a couple of bucks by splicing wires. Intermittent shifting problems occur as the wires start to crack and become progessively worse. My gen 1 LS became almost inoperable until I fixed the broken wires in the hinge.

Yeah I heard about the trunk wire but I couldn't find anything that looked broken or something of the sort. My driving is about 70 city 30 freeway. I'm trying my very best to get the highest mileage possible so thats why this is a bit frustrating. I've heard of people getting mileage better than the EPA rating which is why I'm frustrated since I'm trying to do everything I can to get the highest possible. Hey btw, does anybody know if they get better mileage at higher speeds with this car or not? Cause one example a guy I know gets like 17mpg on the freeway at 60 with his truck and 25mpg with his truck when doing 90. He also gets a similar improvement in mileage when going 90 with his taurus. But because I realize optimal speed varies per car, I'm not expecting much which is why I ask.

[chilkoot]

my '90 ran the same as described directly above, but for the 150 highway miles I've driven my '93 so far my gas gauge is just under 3/4 tank, putting me much higher than the '90, and that was before I did any service to the '93. however, the '90 was fully maintained and got an almost constant 20mpg for any given tank. i'm estimating 25 or more MPG highway on the 93, which sounds in line with what others here have posted.

flushing your fluids should help, and if your spark plugs and wires are more than 75k miles or 5 years old it couldn't hurt to replace them, air filter maybe? the 1uz is capable of more than 17mpg, surely, have you been avoiding maintenance?

[1990LS400]

I think most cases of suspected gas mileage "problems" would be resolved by meticulously keeping track of all the gas that goes into the tank over a long period of time and using a handheld calculator to calculate the exact gas mileages.

Most of the reports I have seen or heard about who say they are getting higher mileage from a gen 1 LS400 were from people who were literally guessing on how much gas they were using rather than making this a scientific exercise. And there are huge differences in driving style and traffic circumstances.

Getting better gas mileage at high speeds is a popular myth. The best gas mileage is almost always attained by driving at a speed just above where the car shifts into its highest gear - usually between 35 and 50 mph on a modern car with auto transmission. This fact is easily verified in later LS cars with built in trip computers by watching the current gas mileage at various speeds.

I know gas is getting expensive compared to the recent past and that is getting a lot of people down. Those with a long term view like me, however, know that, adjusted for inflation, gas is awfully cheap compared to prices in the 60's and 70's.

[Vern Dias]

Getting better gas mileage at high speeds is a popular myth.

I have to disagree with that..... I had a 1998 LX400 for about 5 years and by far the best gas mileage I ever got was on a trip from Texas to Oregon and back via Colorado, Wyoming, Montana, and Idaho. The return was via I5 and I40. Over 4000 miles, at average speeds of 65 MPH and when all was said and done, my trip average was 31 MPG. AC on all the way. My LS400 always turned in the highest mileage on the highway at high speeds.

Just my $.02 and my experience so far. Just got a 2004 LS430 and we'll see how it does.

Vern

[1990LS400]

Getting better gas mileage at high speeds is a popular myth.

I have to disagree with that..... I had a 1998 LX400 for about 5 years and by far the best gas mileage I ever got was on a trip from Texas to Oregon and back via Colorado, Wyoming, Montana, and Idaho. The return was via I5 and I40. Over 4000 miles, at average speeds of 65 MPH and when all was said and done, my trip average was 31 MPG. AC on all the way. My LS400 always turned in the highest mileage on the highway at high speeds.

Just my $.02 and my experience so far. Just got a 2004 LS430 and we'll see how it does.

Vern

Vern, I think the person who started this thread has a little higher mph figure in mind about what he thinks is high speed -- he said 90 mph.

Your 1998 LS400, like my 2000 LS400, has a five speed automatic, a lower coefficient of drag and gets substantially better gas mileage (EPA 19 mpg city; 25 mpg highway) than a gen 1 LS400. At a constant 65 mph (on cruise control) in low/no wind conditions, lightly loaded, tires properly inflated, my 00 LS has more than once done a hair over 27 mpg overall while driving every other weekend from Kansas City to Iowa City before Iowa raised its speed limit from 65 to 70 mph. Yes, I actually obeyed the speed limit.

With a strong tail wind, my 00 LS has slightly exceeded 30 mpg as it did several weeks ago when returning from Tulsa to K.C. with a 40-45 mph tailwind.

Try putting the trip computer in your LS430 on "Current mileage" and see what kind of mileage you get at a constant 55 mph. Then bump up your speed to 65 mph and look at the current mileage. Do all this on flat land in low/no wind conditions. Did your trip computer really show that your mpg is better at 65 than it is at 55 mph?

[Imzjustplayin]

Getting better gas mileage at high speeds is a popular myth.

I have to disagree with that..... I had a 1998 LX400 for about 5 years and by far the best gas mileage I ever got was on a trip from Texas to Oregon and back via Colorado, Wyoming, Montana, and Idaho. The return was via I5 and I40. Over 4000 miles, at average speeds of 65 MPH and when all was said and done, my trip average was 31 MPG. AC on all the way. My LS400 always turned in the highest mileage on the highway at high speeds.

Just my $.02 and my experience so far. Just got a 2004 LS430 and we'll see how it does.

Vern

Vern, I think the person who started this thread has a little higher mph figure in mind about what he thinks is high speed -- he said 90 mph.

Your 1998 LS400, like my 2000 LS400, has a five speed automatic, a lower coefficient of drag and gets substantially better gas mileage (EPA 19 mpg city; 25 mpg highway) than a gen 1 LS400. At a constant 65 mph (on cruise control) in low/no wind conditions, lightly loaded, tires properly inflated, my 00 LS has more than once done a hair over 27 mpg overall while driving every other weekend from Kansas City to Iowa City before Iowa raised its speed limit from 65 to 70 mph. Yes, I actually obeyed the speed limit.

With a strong tail wind, my 00 LS has slightly exceeded 30 mpg as it did several weeks ago when returning from Tulsa to K.C. with a 40-45 mph tailwind.

Try putting the trip computer in your LS430 on "Current mileage" and see what kind of mileage you get at a constant 55 mph. Then bump up your speed to 65 mph and look at the current mileage. Do all this on flat land in low/no wind conditions. Did your trip computer really show that your mpg is better at 65 than it is at 55 mph?

Well the only logic I can deduce from the idea that a higher speed could yeild better mileage than a lower speed for certain vehicles is that the torque curve could jump up dramatically up until the peak torque output and then it levels or drops off from there. So yes if you're driving past your peak torque, you're definately getting worse mileage than otherwise. Also not all vehicles use less fuel at lower RPMs, sometimes it can be quite the opposite and really depends on the engine. Things that have to be accounted for are rolling resistance, drag, power output, and other such things. If an engine can produce 150LBs of torque at 1600rpm and 220LBs of torque at 2000rpm then you'd more likely than not get better mileage with the engine running at 2K rpm and highest gear than at 1600rpm and highest gear. Now if you're getting only 180Lbs of torque at 2000RPM then running at a higher speed probably won't yeild better mileage UNLESS.....from 2000rpm you're getting 180Lbs of torque and at 3200rpm you're getting 320Lbs of torque and other coefficents are factored in then you'd probably get better mileage or similar mileage at that higher RPM.

But because the lexus' peak torque is all the way at 4400rpm and since I can't imagine its torque curve very steep at all and it not consuming more fuel at lower RPMs, I'd imagine that the lowest RPM possible with the highest gear would yeild the best mileage for this car.

[Paul Sherman]

My '93 gets 16-18 mpg wih daily driving, but that's a lot of

stop and go. Mileage-wise, my commute is 12 miles, 7 highway

and 5 city. The city is max speed 35, 9 lights and stop signs,

and St. Louis drivers (Generally regarded by non-natives as

some of the worst in the country - 35+ years driving here

and abroad, I gotta agree). In town, I can't put it in OD without

lugging the engine to 1200-1500 RPM.

Once I get on the freeway and get away from St. Louis,

my mileage can go to 24 mpg easily, sometimes better.

And I'm not guessing, one trip odometer is strictly for

measuring between fill-ups.

[Vern Dias]

I am going on a rerun of this trip later this year in my LS430. It'll be interesting to check out how it goes. Granted, 90 MPH in the US is not doable, but there is a 70 or 80 mile stretch of I-25 in southern Colorado with a posted 80 MPH speed limit. BTW, the LS400 had Michelin MXV4 Energy tires at 34 PSI.

Vern