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All LS400 owners with bad gas mileage READ THIS!

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Old 07-01-14, 12:31 AM   #196
simrx3
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hi,

well i just had my mileage drop off

went from 10.6litres per 100km to 12.2 litres per 100km..

read this a little while ago and remembered it.

bought the sensor and took mine out..

it was stuffed.. the plastic had crystallised and was really brittle..

ive just put the new one in..

so will let yous know if it fixed it..
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Old 02-14-15, 09:37 PM   #197
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I have noticed that temp gauge changes after driving the car for a trip of 1 hour and 30 minutes
So in first 30 minutes of the trip it was between second and third line, while after one hour it was a little above third line, and finally when i reached my destination it was again between second and third line!

Is it thermostat or the ECT?
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All LS400 owners with bad gas mileage READ THIS!-first.jpg   All LS400 owners with bad gas mileage READ THIS!-second.jpg   All LS400 owners with bad gas mileage READ THIS!-third.jpg  
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Old 02-15-15, 06:56 AM   #198
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Quote:
Originally Posted by qewani1 View Post
I have noticed that temp gauge changes after driving the car for a trip of 1 hour and 30 minutes
So in first 30 minutes of the trip it was between second and third line, while after one hour it was a little above third line, and finally when i reached my destination it was again between second and third line!

Is it thermostat or the ECT?
Didn't you read the temperature using an OBD-II tool?
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Old 02-15-15, 11:13 AM   #199
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It looks like you thermostat might be stuck open. Like Yamae suggested you should buy a cheap obd-II tool to read the actual temp though.
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Old 02-15-15, 09:04 PM   #200
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Quote:
Originally Posted by Yamae View Post
Didn't you read the temperature using an OBD-II tool?
Again went for a trip of 2 hours during night where outside temp was 18, but this time took my OBD2 scanner to read the ECT values.. I have noticed that Temp gauge drops only when car is moving, but on idle it reads 77, while when car moving it reads lower 70 !!
As am seeing, temp gauge is reading the actual values.., so it means ECT is working fine
Is that normal?
attaching below the readings...
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All LS400 owners with bad gas mileage READ THIS!-img_3156.jpg   All LS400 owners with bad gas mileage READ THIS!-img_3157.jpg   All LS400 owners with bad gas mileage READ THIS!-img_3154.jpg  
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Last edited by qewani1; 02-15-15 at 09:08 PM.
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Old 02-16-15, 05:07 PM   #201
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After 2 hours of driving the temp should be around 180-190 degrees which would be the cars operating temperature. if it's only reading 77 then dropping to 70 then the car is not heating up properly and thats probably because your thermostat is stuck open. If your coolant was low you would be overheating instead the car is not even getting to operating temp. Does your heat blow hot or warm?
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Last edited by sha4000; 02-16-15 at 08:13 PM.
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Old 02-16-15, 07:48 PM   #202
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Quote:
Originally Posted by qewani1 View Post
Again went for a trip of 2 hours during night where outside temp was 18, but this time took my OBD2 scanner to read the ECT values.. I have noticed that Temp gauge drops only when car is moving, but on idle it reads 77, while when car moving it reads lower 70 !!
As am seeing, temp gauge is reading the actual values.., so it means ECT is working fine
Is that normal?
attaching below the readings...
As I told you 2 weeks ago.
http://www.clublexus.com/forums/ls40...ml#post8898726

It may shorten your engine life to run highway with a low temp condition. It's also bad for the gas mileage. You'd better fix it quickly.
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Old 02-16-15, 09:14 PM   #203
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Quote:
Originally Posted by sha4000 View Post
After 2 hours of driving the temp should be around 180-190 degrees which would be the cars operating temperature. if it's only reading 77 then dropping to 70 then the car is not heating up properly and thats probably because your thermostat is stuck open. If your coolant was low you would be overheating instead the car is not even getting to operating temp. Does your heat blow hot or warm?
180-190 degrees fahrenheit or celsius ?
The temperatures which i mentioned in my previous post are in Celsius, during the day driving the temp needle reads 85 Celsius, what i mentioned is only during night driving
heat blows hot

Quote:
Originally Posted by Yamae View Post
A slow temperature rise is mostly caused by a worn thermostat. The ECT sensor only detects the temperature. It doesn't have a long time constant. It only has about 10 seconds of it.
As per your old post Do you recommend me to change the thermostat ?
My current highway MPG is 20 only!
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Last edited by qewani1; 02-16-15 at 09:18 PM.
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Old 02-17-15, 04:29 PM   #204
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I was talking about Fahrenheit so if it's 85 Celsius then the car is getting to operating temp. i would change the thermostat . It's a cheap and easy fix.
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Old 02-17-15, 05:01 PM   #205
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Quote:
Originally Posted by qewani1 View Post
As per your old post Do you recommend me to change the thermostat ?
My current highway MPG is 20 only!
The early bird gets the worm. A slow fix damages the car more and looses the money. If I were you, I would enjoy better drive feeling and better gas mileage changing the thermostat quickly. Improved gas mileage would be quickly more than the cost of the thermostat and that $ will be added more and more in the future.
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Old 02-17-15, 08:34 PM   #206
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could i have the OEM part numbers of the Thermostat and gasket for LS400 2000?
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Old 03-26-15, 08:49 AM   #207
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Have a 1993 LS400 with 150K miles. I have changed the temperature sensor about a month ago and did ABSOLUTELY NOTHING to the gas mileage. Still get between 12-15MPG here in California. Basically if your temp needle is moving up to the 35-40% (near the 3rd line) and you get good heat coming from the heater, DON'T CHANGE THE ECT sensor, won't do anything for you!

However two days ago I serviced the car and have the throttle body cleaned plus fuel injector cleaning at the Lexus dealer, after the service the car felt totally transformed! I felt the engine HP has increased significantly and gas mileage has improved to 18MPG!

I think I have finally fixed my bad mileage issue. A dirty engine is very much more likely the main culprit compare to any sensor issue, especially if your car is not throwing any codes.

My engine coolant temperature is always maxing out at the 3rd line (~40%) and will dip down a bit during highway driving in the winter, to perhaps ~35%, between the 2nd and 3rd line. This behavior is absolutely normal and no cause for concern.

Hope this helps you folks with high mileage LS400s.

Last edited by tomgadgets; 03-30-15 at 01:45 AM.
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Old 04-27-15, 10:28 AM   #208
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So after reading this thread, i planned to change my sensor. It was totally bad when i pulled it out, the main problem i had was findig the correct sensor as it has 2 sensors. I ordered one from amazon and it was smalled thn the factory one. So i had to get one from dealership as the sensor was broken and since i have changed it i can see a huge difference in mileage. First my half tank used to stay for 2 and half day of driving on freeway but now i did 5 days with just a little over half gas tank. I am very happy with this. U should change it too.
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