1996 Ls400 Gas Mileage Issues, Slow To Warm Up

[yotoy82]

I have a 1996 LS400 I just bought with 204,000 Miles on it, all the paper work, properly maintained, beautiful condition actually. The only problem I noticed when I bought it in the summer was that the engine temperature needle never went to the exact middle like my fathers 1995 LS400. Mileage was alright, 23 highway average, not horrible, not great. And I drive VERY light footed. Then when winter came, I noticed the car took FOREVER to get warm. I changed the thermostat myself, the old one was the original, the center copper part was all scratched up, I assume from jamming up. It heats up only a BIT faster now but doesn't go all the way to the middle unless I get on the interstate and drive it hard, otherwise It still takes forever to warm up!

I also changed the air filter. I drive mostly in the city, and the last two tanks, exclusively in the city, I get about 75 miles until the needle comes to the halfway point. To put it bluntly, highway and city driving mix, I'm getting 13 mpg, and just city driving I'm getting a whopping 8 mpg!!!

Its been using 5w30 oil most of its life, but had 10w30 put in by accident when I got an oil change because forgot to mention it to the dealer, but I don't think this would make that much of a difference, although I intend to use 5w30 exclusively year round in it on the next oil change. It passed the emission testing just fine according to his paper work September 2008 at 182000 miles. No paperwork on oxygen sensors ever being changed though. No check engine lights on. It drives just fine, no funny sounds at all, smooth as butter. It is a bit rough while its cold and slow accelleration, but when it finallllly gets warm, it drives like a ROCKET.

Paperwork shows lexus dealership in Naperville, Illinois changed the rotors, caps, wires and plugs at 144,000 miles Feb 2006, so I'm assuming they are platinum and have plenty of good life left in them!

I ordered an OEM Coolant Sensor based on other threads, should be coming in soon and am hoping thats the problem. I also changed the FUEL FILTER and a PCV Valve . Can anyone else tell me if I'm missing something else that I should check, any help would be greatly appreciated (my wallet would appreciate it too!)

The main concerns are why after a thermostat change does it still take forever to get warm, and why is the mileage HORRIBLE! And maybe the two are related to each other. I also tried "blurping the air" out of the coolant system, no effect. Please someone help!

[curiousB]

I wouldn't go crazy trying to get the needle to hit an exact point. The dash gauge isn't meant to be a highly calibrated reading. I am more concerned with your time to heat up.

You said you put in a new thermostat. Was it OEM or aftermarket? Just wondering if it is a substitute with a different cut in temperature point. maybe test it in a boiling pot of water to see that it doesn't open too early. Also are you sure the system is purged of all air? I leaned in a recent post here the "jiggle valve" on the thermostat would be positioned to the highest point to allow the air to pass and get coolant touching the wax container portion of the thermostat. Air blockages usually result in over heating though.

The very low fuel performance is a troubling sign. The car shouldn't take 75 miles to warm up. I'd sort through that first. It just not that cold here in IL, ask some of the people in Canada about what cold is.

A bad temp sensor could be fooling the ECU about engine temp and driving too rich a fuel mix and explain the poor mileage you are getting. I think there are two temp sensors on your car. One for the dash indicator and one for the ECU. Fixing one doesn't fix the other.

[SRK]

Drive the car for fifteen minutes, then lift the hood and with the engine running carefully grab the upper rad hose. It should be hot enough to make you want to let go, but not burn you. If it is comfortably warm only then you have a faulty thermostat. That's the test I use and it works every time.

[yotoy82]

I wouldn't go crazy trying to get the needle to hit an exact point. The dash gauge isn't meant to be a highly calibrated reading. I am more concerned with your time to heat up.

You said you put in a new thermostat. Was it OEM or aftermarket? Just wondering if it is a substitute with a different cut in temperature point. maybe test it in a boiling pot of water to see that it doesn't open too early. Also are you sure the system is purged of all air? I leaned in a recent post here the "jiggle valve" on the thermostat would be positioned to the highest point to allow the air to pass and get coolant touching the wax container portion of the thermostat. Air blockages usually result in over heating though.

The very low fuel performance is a troubling sign. The car shouldn't take 75 miles to warm up. I'd sort through that first. It just not that cold here in IL, ask some of the people in Canada about what cold is.

A bad temp sensor could be fooling the ECU about engine temp and driving too rich a fuel mix and explain the poor mileage you are getting. I think there are two temp sensors on your car. One for the dash indicator and one for the ECU. Fixing one doesn't fix the other.

My dad has a 95 LS400, and it heats up in 10 minutes MAX and the needle goes to the halway point, they are essentially the same car which is why I'm guessing mine should too.

Hot air comes out after bout 10 minutes, but doesn't really get that hot until the engine is as heated up as it will get. I used a New OEM Toyota/Lexus Thermostat and Gasket. I used OEM Toyota Red Coolant mixed 50/50 with distilled water. I don't remember off hand where the jiggle valve was, but read about it later on too, don't want to open it up again, but I do remember putting it exactly the way the original one was on.

It takes about 15-20 minutes to warm up. When I say warm up, I mean to get to the optimal operating temperature. I know the temperature gauge inside the car isn't spot on but its pretty accurate, because when the car is cold you can hear the engine reving up more than normal and the rpms are high and when it FINALLY gets to the middle almost is when the rpm's slow down to 5-600 and the engine gets super quiet and smooth. Also, the heater is on auto and like the lexus does, it slowly raises the fan speed according to the engine temperature so only when the engine gets warm does the heater blow with full speed.

Also, on my dads 95 LS400, heater blows full speed quite quick, also indicated a fast warming engine. If it gets fully warm, turn it off for 30-60 min, and start it up again, in 5 minutes tops its back to full operating temperature. My 96 LS400 well, after 30-60 minutes its pretty much back to cold again and waiting a lot longer to warm up.

But ya, its only giving me 8 miles per gallon in the city now which is driving me crazy, all I can contemplate is that it has something to do with the engine not warming up. One thing is for sure, when the car gets warm, the heater blows out plenty of powerful heat.

Will try checking the radiator hose like SRK says as well next time I go out. Appreciate the replies.

[landar]

You are fortunate to have your dad's LS nearby for comparison. That certainly helps. You might consider buying an infrared thermometer to check various spots on the engine for comparison. The thermometers are really pretty inexpensive these days (maybe $35-45) and are wonderful supplements to the toolbox. Takes the guesswork out of "feeling" the heat.

I have one similar to this:

http://www.google.com/products/catalog?client=safari&rls=en&q=infrared+thermometer&oe=UTF-8&um=1&ie=UTF-8&cid=12955984420802696606&ei=W4AaTe2QLc29nAfqivm5Dg&sa=X&oi=product_catalog_result&ct=result&resnum=2&ved=0CEMQ8wIwAQ#ps-sellers

[handygal]

I've had a 95 SC400, I have a 98 LS400 now and my mom has an 03 GS400. We've had all 3 since new and none of them goes to the middle point, they are all under and always have been. I had a thermostat issue with the car before the SC so I tend to keep a mental note of every car's normal, I'm not getting stranded by that again.

You really do have something going on though. I wouldn't be surprised if you have 2 things going on.

I'm hoping that sensor fixes your mileage issue, I've been considering changing mine too.

[yotoy82]

Ya I bought the OEM coolant sensor, just haven't gotten around to putting it in yet, seems like a lot of plastic covers to take off to get to it. Heres a picture of how high the needle gets after about 20 minutes. The rpm's seem kinda low when stopped and gear in drive, but when I put it in park it goes back up to 600, but the car is still perfectly smooth even at 400.

[SRK]

That's the normal position for the temperature gauge. Thermostat is working.

You are thinking of the ECU coolant temp sensor, not the gauge sensor correct? Many parts people are messed up on the difference.

[rezonans]

Does yuor idle air control system(IDLE) operates properly ? May be you need a simple cooling system flush http://www.autozone.com/autozone/accessories/Prestone-33-8-oz-super-radiator-cleaner/_/N-262g?counter=4&itemIdentifier=525162_0_0_ it helps me to improve my cooling.

[curiousB]

May be you need a simple cooling system flush http://www.autozone.com/autozone/accessories/Prestone-33-8-oz-super-radiator-cleaner/_/N-262g?counter=4&itemIdentifier=525162_0_0_ it helps me to improve my cooling.

Flushing is generally to cure overheating when the rad and cooling system won't release the heat to the atmosphere. This is the opposite problem here so flushing won't likely help.

[yotoy82]

That's the normal position for the temperature gauge. Thermostat is working.

You are thinking of the ECU coolant temp sensor, not the gauge sensor correct? Many parts people are messed up on the difference.

Ya, the ECU Coolant temp sensor, hoping to get to it today, not the gauge sensor.

[rezonans]

Do you check your cooling fan may be it work all the time and dont let engine warm up quick.

[yotoy82]

Do you check your cooling fan may be it work all the time and dont let engine warm up quick.

You know something, that actually crossed my mind, I just never checked it, doubt it is it but never know. You mean the fan in front of the radiator? It should not be on when I first turn on the car right?

[SRK]

No it only comes on with engine coolant temp when the engine driven fan can't keep up, or excessive AC pressures, or when certain trouble codes are tripped.

So you are saying......?

[yotoy82]

Ok, well I noticed there are two fans. One on the outside of the radiator, it doesn't turn on when I start the cold car, but the one on the inside of the radiator starts up right away. That one is supposed to be running all the time or only when engine is warm??

Ok, I checked my dads working fine LS400 to compare. There are 2 fans , one on the outside, black, one on the inside, white. On my dads car even the white fan turns on right away so I guess thats normal

[rezonans]

I mean fan which is connected to the drive belt of the engine that is the cooling fan, that one that you have on your pictures that is ac fan.

[yotoy82]

Well I doubt its the fans, they are all working properly.

Changed the coolant sensor today, the old one was cracked/broken and corroded pretty bad!! Heres a picture, I hope this was the problem, will find out when I fill up and check the mileage again

[yotoy82]

I mean fan which is connected to the drive belt of the engine that is the cooling fan, that one that you have on your pictures that is ac fan.

ya, the fan connected to the drive belt of the engine, the cooling fan, its on all the time always

[VBdenny]

That is exactly where my temperature gauge stays all the time. Since it has been like that for many, many years, I will assume it is normal. My car takes a long time to warm up so I expect that is typical as well. I don't think you have any problem.

[yotoy82]

That is exactly where my temperature gauge stays all the time. Since it has been like that for many, many years, I will assume it is normal. My car takes a long time to warm up so I expect that is typical as well. I don't think you have any problem.

Ya, except that I'm getting about 8 miles per gallon or about 120 miles per tank right now. Its been slowly getting worse each fill up, I have no idea why. Changed the sensor so can only hope that was the problem.

[VBdenny]

8mpg? then you do have a problem. I get around 17-18 in the city. Time to go to Autozone or Advance and use their OBDII

[yotoy82]

I dont have a check engine light on, will they still do a check?

[Banshee365]

I'm interested to hear what your results are after you install the new ECT sensor. Make sure to disconnect your negative battery cable for several minutes and start the adaptive learning strategy over from scratch. I've been down this road with my '96 with ECT problems. The car never thought it was warming up so it kept pouring fuel into the engine (even when warm) to the point where it would flood out and refuse to start until it cooled. My problem ended up being the ECM. Many others have had great sucess in renewing lost power and economy with a new ECT sensor.

[yotoy82]

Yah, I'll keep you posted, haven't had time to drive much or go to the gas station and fill up and see how it works. Thanks for the reminder on the battery disconnecting, I removed one terminal, not sure if it was the negative or the positive, does it matter which one? I removed one, the car was dead for 10 minutes, when I reconnected it and turned it on the clock was reset and trip meter etc. A weird thing I noticed is the FRONT DEFROST button light turned red and flashed intermittently for like 60 seconds, and the climate control thing was dead, super weird, never saw a read light on it before, but after a minute it self reset and then started working.

[Banshee365]

It doesn't really matter which cable you pull. I just alway's do the negative.

The light on the AC panel is just what you thought, completely normal It's just finding it's place in this world again.