1996 Ls400 Gas Mileage Issues, Slow To Warm Up

curiousB · January 6, 2011

Either line will disconnect power. Its generally safer to disconnect negative first. If you do positive and accidentally have wrench touch chassis you'll get a nasty surprise. Not so if you do negative first.

yotoy82 · January 6, 2011

Good idea, I'll remember that next time! It's still taking forever to warm up though, but the heating comes out a bit faster. Will keep you posted on the mileage results.

MEDO · January 8, 2011

Do you replaced the ECT ? Is that affect on the warming-up time and fuel consumption?

Please post, I have the same problem.

yotoy82 · January 10, 2011

I filled up yesterday, and the fuel needle is still moving down really fast! I suspect my problem isnt solved yet, but will wait until half a tank is empty and fill up and see the mileage I got. It is still taking a long time to warm up! I'm quite sure the bad gas mileage I'm having is directly related to the car taking forever to warm up because this problem did not exist in the summer. I also did an oil change today too with Mobil-1 5w30 synthetic extended performance, I really am hoping the problem is solved, lets see.

landar · January 11, 2011

I filled up yesterday, and the fuel needle is still moving down really fast! I suspect my problem isnt solved yet, but will wait until half a tank is empty and fill up and see the mileage I got. It is still taking a long time to warm up! I'm quite sure the bad gas mileage I'm having is directly related to the car taking forever to warm up because this problem did not exist in the summer. I also did an oil change today too with Mobil-1 5w30 synthetic extended performance, I really am hoping the problem is solved, lets see.

The oil change is nice but will do nothing noticeable for your mileage.

It sure seems like the thermostat is open although you mentioned that you replaced it. Do you remember the value stamped on the thermostat? Maybe you got the wrong thermostat.

Depending upon where you live (btw,where do you live?) and current cold weather, it could take anywhere from 5-15 minutes for the engine to warm up. This assumes you are driving a modest 35-50 MPH down the road. Normally, in this weather (25F in Indiana), it will take about 10 minutes for my engine to be 95% warmed. If the temp gauge is taking in the area of 20 minutes to come to full operating temp, you have a problem in the coolant area. Here are a couple of suggestions. Feel free to try (or not) :)

1) Make some measurements. You dont need a stopwatch but try to get reasonably accurate. From dead cold, start and drive down the road at around the speed limit. How long does it take for the needle to get to "normal"?

2) After getting it up to full temp, find a stretch of flat road where you can keep the speed constant, in the 50-60 mph range. What does your instantaneous(current) MPG readout indicate?

3) If your engine is taking in the 20 minute range to warm up, consider putting a piece of cardboard in front of the radiator (cut to fit so it is safe to drive) and do test #1 again. Does it now warm up much quicker? Do not leave the cardboard on there except for the short test drive or you could overheat. And keep a close eye on the temp gauge if you try this one. This test would confirm an open thermostat, stuck-on fan, etc.

yotoy82 · January 11, 2011

I filled up yesterday, and the fuel needle is still moving down really fast! I suspect my problem isnt solved yet, but will wait until half a tank is empty and fill up and see the mileage I got. It is still taking a long time to warm up! I'm quite sure the bad gas mileage I'm having is directly related to the car taking forever to warm up because this problem did not exist in the summer. I also did an oil change today too with Mobil-1 5w30 synthetic extended performance, I really am hoping the problem is solved, lets see.

The oil change is nice but will do nothing noticeable for your mileage.

It sure seems like the thermostat is open although you mentioned that you replaced it. Do you remember the value stamped on the thermostat? Maybe you got the wrong thermostat.

Depending upon where you live (btw,where do you live?) and current cold weather, it could take anywhere from 5-15 minutes for the engine to warm up. This assumes you are driving a modest 35-50 MPH down the road. Normally, in this weather (25F in Indiana), it will take about 10 minutes for my engine to be 95% warmed. If the temp gauge is taking in the area of 20 minutes to come to full operating temp, you have a problem in the coolant area. Here are a couple of suggestions. Feel free to try (or not) :)

1) Make some measurements. You dont need a stopwatch but try to get reasonably accurate. From dead cold, start and drive down the road at around the speed limit. How long does it take for the needle to get to "normal"?

2) After getting it up to full temp, find a stretch of flat road where you can keep the speed constant, in the 50-60 mph range. What does your instantaneous(current) MPG readout indicate?

3) If your engine is taking in the 20 minute range to warm up, consider putting a piece of cardboard in front of the radiator (cut to fit so it is safe to drive) and do test #1 again. Does it now warm up much quicker? Do not leave the cardboard on there except for the short test drive or you could overheat. And keep a close eye on the temp gauge if you try this one. This test would confirm an open thermostat, stuck-on fan, etc.

1. I don't remember the exact part number of the thermostat, I ordered it from http://mylexparts.com , it was a toyota thermostat, looked exactly like the factory one which I took out, so 99% sure it's the right thermostat.

2. I had 10w30 in before, 5w30 made a big difference in that the car doesn't idle as high when start it up in the morning and the heat starts coming out the heater 50% faster, but the car still takes long to warm up, although not as long as it had previously.

3. I live in central Illinois so probably have the same weather you do in Indiana. I'd say it takes a good 15-20 minutes to get fully warmed up with driving around the city , speeds from 30-45 mph.

4. I used "Toyota Red Coolant", mixed 50% coolant and 50% distilled water when I filled it up.

5. My 1996 LS400 does not have a miles per gallon read out unfortunately! The only way I can calculate mileage is by filling up, resetting the tripmeter driving around the city as I normally do and fill up around half a tank and calculate how many gallons it took to fill up and see how many miles I had driven.

6. Explain the cardboard procedure, you mean cut out a big square piece of cardboard and cover the entire front of the radiator with it so wind doesn't blow on it?

Appreciate you taking the time to help.

landar · January 12, 2011

I forgot the earlier versions may not have had the economy readout. The cardboard is an old "trick" and still used some today("big rig trucks") in very cold sections of the country to restrict air flow through the radiator and allowing an engine to warm more quickly. You have the right idea. It goes directly in front of the radiator...well not sure how much the fans would get in the way. You could potentially just disconnect the fans so they did not start up and see if that makes any difference. But just for a little test drive. Remember to reconnect them afterwards if you decide to try it. You would still have the main clutch fan possibly pulling air through the radiator, hence the need for some restriction for the test.

MEDO · January 12, 2011

I forgot the earlier versions may not have had the economy readout. The cardboard is an old "trick" and still used some today("big rig trucks") in very cold sections of the country to restrict air flow through the radiator and allowing an engine to warm more quickly. You have the right idea. It goes directly in front of the radiator...well not sure how much the fans would get in the way. You could potentially just disconnect the fans so they did not start up and see if that makes any difference. But just for a little test drive. Remember to reconnect them afterwards if you decide to try it. You would still have the main clutch fan possibly pulling air through the radiator, hence the need for some restriction for the test.

Indeed, I was have the same problem (slow warm up) .. I tried to put piece of cardboard in front of radiator to minimize air quantity blowing by main mechanical fan .. Also I checked the Thermostat, by put it in a boiling water, (its opened with no problem..and its closed when put it in cold water). But I observed a very small piece of the rubber ring is broken, and when Thermostat closed at cold state, its remaining to leaks some water through the closed gate, just I removed all that rubber ring and that makes the gate closing completely .. Then I return it back in its hose .. Its work ... Now I need about 6 minutes only to warm up to the normal state and return the RPM to 800 from 1400. :rolleyes:

yotoy82 · January 13, 2011

I forgot the earlier versions may not have had the economy readout. The cardboard is an old "trick" and still used some today("big rig trucks") in very cold sections of the country to restrict air flow through the radiator and allowing an engine to warm more quickly. You have the right idea. It goes directly in front of the radiator...well not sure how much the fans would get in the way. You could potentially just disconnect the fans so they did not start up and see if that makes any difference. But just for a little test drive. Remember to reconnect them afterwards if you decide to try it. You would still have the main clutch fan possibly pulling air through the radiator, hence the need for some restriction for the test.

Indeed, I was have the same problem (slow warm up) .. I tried to put piece of cardboard in front of radiator to minimize air quantity blowing by main mechanical fan .. Also I checked the Thermostat, by put it in a boiling water, (its opened with no problem..and its closed when put it in cold water). But I observed a very small piece of the rubber ring is broken, and when Thermostat closed at cold state, its remaining to leaks some water through the closed gate, just I removed all that rubber ring and that makes the gate closing completely .. Then I return it back in its hose .. Its work ... Now I need about 6 minutes only to warm up to the normal state and return the RPM to 800 from 1400.

Can you explain exactly I didn't really understand what you are saying. That there was leaks and fluid was still going to the engine?

Which rubber ring are you talking , is there rubber on the actual thermostat or are you talking about the thermostat gasket or something else completely, please let me know!

MEDO · January 13, 2011

I forgot the earlier versions may not have had the economy readout. The cardboard is an old "trick" and still used some today("big rig trucks") in very cold sections of the country to restrict air flow through the radiator and allowing an engine to warm more quickly. You have the right idea. It goes directly in front of the radiator...well not sure how much the fans would get in the way. You could potentially just disconnect the fans so they did not start up and see if that makes any difference. But just for a little test drive. Remember to reconnect them afterwards if you decide to try it. You would still have the main clutch fan possibly pulling air through the radiator, hence the need for some restriction for the test.

Indeed, I was have the same problem (slow warm up) .. I tried to put piece of cardboard in front of radiator to minimize air quantity blowing by main mechanical fan .. Also I checked the Thermostat, by put it in a boiling water, (its opened with no problem..and its closed when put it in cold water). But I observed a very small piece of the rubber ring is broken, and when Thermostat closed at cold state, its remaining to leaks some water through the closed gate, just I removed all that rubber ring and that makes the gate closing completely .. Then I return it back in its hose .. Its work ... Now I need about 6 minutes only to warm up to the normal state and return the RPM to 800 from 1400.

Can you explain exactly I didn't really understand what you are saying. That there was leaks and fluid was still going to the engine?

Which rubber ring are you talking , is there rubber on the actual thermostat or are you talking about the thermostat gasket or something else completely, please let me know!

Well, during test the thermostat by lifting from the place and put it in a basin of boiling water then in cold water, and when the gate is closed, I noticed water leaking from the gate because of damage gasket surrounding the holding of which does not allow rubber clasps tightly to the gate .. Means that even in the case of closure of thermostat, still leaking water from it .. so, this car does not heat up because of the continuation of water circulation.

So, you need to checkup the thermostat and the temperature sensor

yotoy82 · January 13, 2011

I forgot the earlier versions may not have had the economy readout. The cardboard is an old "trick" and still used some today("big rig trucks") in very cold sections of the country to restrict air flow through the radiator and allowing an engine to warm more quickly. You have the right idea. It goes directly in front of the radiator...well not sure how much the fans would get in the way. You could potentially just disconnect the fans so they did not start up and see if that makes any difference. But just for a little test drive. Remember to reconnect them afterwards if you decide to try it. You would still have the main clutch fan possibly pulling air through the radiator, hence the need for some restriction for the test.

Indeed, I was have the same problem (slow warm up) .. I tried to put piece of cardboard in front of radiator to minimize air quantity blowing by main mechanical fan .. Also I checked the Thermostat, by put it in a boiling water, (its opened with no problem..and its closed when put it in cold water). But I observed a very small piece of the rubber ring is broken, and when Thermostat closed at cold state, its remaining to leaks some water through the closed gate, just I removed all that rubber ring and that makes the gate closing completely .. Then I return it back in its hose .. Its work ... Now I need about 6 minutes only to warm up to the normal state and return the RPM to 800 from 1400.

Can you explain exactly I didn't really understand what you are saying. That there was leaks and fluid was still going to the engine?

Which rubber ring are you talking , is there rubber on the actual thermostat or are you talking about the thermostat gasket or something else completely, please let me know!

Well, during test the thermostat by lifting from the place and put it in a basin of boiling water then in cold water, and when the gate is closed, I noticed water leaking from the gate because of damage gasket surrounding the holding of which does not allow rubber clasps tightly to the gate .. Means that even in the case of closure of thermostat, still leaking water from it .. so, this car does not heat up because of the continuation of water circulation.

So, you need to checkup the thermostat and the temperature sensor

I'm having trouble understanding you a little bit, are you saying the "Actual THERMOSTAT" itself had a problem allowing fluid flow in, or are you talking about the gasket surrounding the thermostat that keeps it in place. Thermostat is one part, and thermostat gasket is another part, are you saying there is rubber on the actual thermostat that was broken? Or are we talking about another part? My thermostat is new so I doubt any issues with it exactly!

I'm also tired at this stage, thinking of going for an aftermarket thermostat that opens at 190 degrees or something

etex · January 13, 2011

Just my guess, but I think he is referring to the rubber gasket which surrounds the outer perimeter of the thermostat. Be sure the one you put in had this in place.

landar · January 13, 2011

yotoy, I am guessing as well, but I think medo is saying a piece of the gasket was torn and allowed coolant to bypass the TS. I honestly cant see a torn gasket allowing THAT much coolant to bypass... but maybe, depending upon the severity of the damage.

Did you try blocking the radiator and see if the engine warmed any quicker? You really just need to block the front grill in order to keep air from flowing through the radiator. A simple "bra" over the front grill will do.

Again, this is just to verify what is causing the slow warming. If blocking the air flow helps, it points to a bad TS or gasket. If it makes no difference, then there may be a sensor that is misbehaving. I know it can seem frustrating but slow engine warming "should" be relatively easy to pinpoint. Remain meticulous in all the testing and you will soon have it nailed. Any heating time measurements for us to digest yet?

yotoy82 · January 14, 2011

yotoy, I am guessing as well, but I think medo is saying a piece of the gasket was torn and allowed coolant to bypass the TS. I honestly cant see a torn gasket allowing THAT much coolant to bypass... but maybe, depending upon the severity of the damage.

Did you try blocking the radiator and see if the engine warmed any quicker? You really just need to block the front grill in order to keep air from flowing through the radiator. A simple "bra" over the front grill will do.

Again, this is just to verify what is causing the slow warming. If blocking the air flow helps, it points to a bad TS or gasket. If it makes no difference, then there may be a sensor that is misbehaving. I know it can seem frustrating but slow engine warming "should" be relatively easy to pinpoint. Remain meticulous in all the testing and you will soon have it nailed. Any heating time measurements for us to digest yet?

Haven't had time to do the thermostat test yet. I used a brand new thermostat and gasket, original toyota/lexus parts. All I can imagine is that I installed it wrong because I don't remember, maybe I had the jiggle valve upside down or the thermostat not aligned exactly the same as the old one, going to open it up again soon as weather gets better and see if I can find a problem!

Haven't had time to do the cardboard test, its just so cold outside to be messing around. I drove my dads white ls400 like 3 miles to mcdonalds from dead cold and it was fully warmed up in like six minutes.

But My LS400, haven't timed it exactly yet but I would safely say it takes 20 minutes to get fully warmed. If I turn the car off even for 30 minutes, it will be fully cold again and will take about 15 min to rewarm again whereas other cars once they fully warmed if you turn them off, go shop around and come back and turn it back on, it will warm up even twice as fast, its almost like some magic ghost is sucking the heat from my engine, it just won't preserve the heat!

yotoy82 · January 16, 2011

Still haven't tried the cardboard trick but after engine was warm, filled up and drove 40 miles on the interstate, pulled over filled up again, averaged 25 mpg on the interstate. But still averaging 9 mpg in the city! I'm guessing the mileage issue is because of the engine not warming up, can a cold engine really make that much of a difference, I know I should be getting 18 mpg in the city the way I drive.

landar · January 17, 2011

its almost like some magic ghost is sucking the heat from my engine, it just won't preserve the heat!

Well I can assure you that there is no magic ghost sucking the heat from your engine. Thermodynamics is the same for your engine block as it is for your dad's LS. Now, if you take your car to the dealer, there IS a magic ghost that will suck the money from your wallet. But that's a different subject.

Your test of 40 miles on the interstate is probably too short to get an accurate reading. I suspect ditto for your city test. But yes, your car will get much worse mileage when cold than when hot.

yotoy82 · January 17, 2011

its almost like some magic ghost is sucking the heat from my engine, it just won't preserve the heat!

Well I can assure you that there is no magic ghost sucking the heat from your engine. Thermodynamics is the same for your engine block as it is for your dad's LS. Now, if you take your car to the dealer, there IS a magic ghost that will suck the money from your wallet. But that's a different subject.

Your test of 40 miles on the interstate is probably too short to get an accurate reading. I suspect ditto for your city test. But yes, your car will get much worse mileage when cold than when hot.

I'm confident on my results which I keep track of over the last 2 months. 6-11 mpg in city, and 25 mpg on the interstate. I usually make short trips to work and home a few times a day, so tats like start, drive 3 miles, sit for a few hours, drive back etc. At 50-70 miles on the odometer later, half the tank is empty.

If I drive on a trip on the interstate, ie from here to st. louis which is about 90 min, I'll easily get at least 150 miles before the tank is half. I'm sure if there was some issue causing poor mileage in general that it would show across the entire spectrum, ie the interstate mileage would be poor too!

I have a good dealer I go to, guess will wait and see.

Ruud · February 13, 2011

any updates about this?

VMF · February 13, 2011

its a known issue on the early Ls, mine did the same thing, from what i was able to find out talking to one of the lexus tech ppl, is that it is a software issue but since it doesnt really cause any issues they never bothered to fix it

lucymiao · February 14, 2011

i have similar problem with fuel efficiency with my 1997 Lexus LS400, but I have no heating problem.

I have changed the air filter this weekend.

Going to change the Spark Plugs with NGK General Platinum.

My questions:

Should I change O2? What is O2 by the way, just seeing other people mentioning it?

Injector cleaner (Lucas brand) will be helpful?

Anything I shall do to improve fuel efficiency?

Thanks

yotoy82 · February 15, 2011

any updates about this?

So far the problem not solved. I'm convinced the mileage issue is related to the engine not being warm/optimal temperature. Going to buy an aftermarket higher temperature thermostat and see if that fixes the problem!

Ondro1977 · March 22, 2011

Hi guys, here is 3 month old owner of 1997 Lexus LS 400 Base with 150 000 miles. That means I have same car as 1995, 1996. It is 1UZ-FE 8cyl 32valve 4litre.. it is NOT VVT-i(1998-2000) Variable valve timing engine---just to be clear. I have very similar issue about car heating up slowly and temperature gauge NEVER reaching mid point. My average city used to be no more than 13 MPG ,and I am extremely light footed. I recently changed oil (Quaker state mineral- 5W-30)FRAM extended mileage oil filter, PUROLATOR air filter, and most importantly DENSO spark plug wire set and DENSO Platinum TT Plugs. Wires were still original 1996 and plugs (especially two on both sides close to cabin Rusted!!) Since then, It feels like car is more civilized and looks like fuel economy slightly improved to 15 MPG in the city. but car still takes long time to warm up and I also believe it is related with fuel economy,that with my style of driving should be at least 17 MPG.

Is it:

1) bad temperature sensor fooling ECU?

2)rusted or stuck up cooling system( needed flush)?

3)stuck up open thermostat?

4)cooling fan working constantly (faulty on/off switch??)

or any other issue I am not aware of??

I would really appreciate reliable help on this subject

curiousB · March 24, 2011

Is it:

1) bad temperature sensor fooling ECU?----->>>>>>Maybe, pretty inexpensive to fix (there are two temp sensors replace the ecu one...)

2)rusted or stuck up cooling system( needed flush)? --------->>>> doubtful this would lead to overheating not slow heating

3)stuck up open thermostat? --------->>>>> maybe and easy and inexpensive to replace. I'd start with this

4)cooling fan working constantly (faulty on/off switch??) might be a problem but not the reason you are slow to warm up...

yotoy82 · May 30, 2011

Just a quick update for everyone, I took my LS400 to a local mechanic, has good reviews but a little expensive. He checked the fuel trim levels and said it had a biased lean. After looking around, he said the mass air flow sensor didn't seem right or something like that. There were no codes or anything like that, but he said its possible it was out of calibration etc. We had another LS400 of the exact model that was getting great mileage. Changed the MAF sensor w/the other car and checked the fuel trim levels, and viola, no more biased lean. I didn't want to buy a new one or a remanufactured one, I mean how often do these go bad on a 96 LS400, bought one on eBay for $100, and so far it seems to have helped, fuel trim levels are great. Now I've driven a little bit in the city and the interstate, and the gas gauge is at 3/4 still after driving 80 miles, where usually 80 miles was close to half empty. Let's hope my gas mileage problem is solved!

R White · June 23, 2011

I managed to boost the mileage on my 96 LS400 (103,000 miles) from between 18-19 mpg to 24.5 mpg (mostly highway miles) by changing oil to Amsoil 0-30w and running Amsoil's PI injector cleaner through the engine (you put the cleaner into a full tank every 4000 miles). I'm NOT an Amsoil distributor and I am a leadfoot driver so I never get the best mileage, but this improvement totally sold me on Amsoil products.