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All LS400 owners with bad gas mileage READ THIS!

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Old 08-31-08, 12:51 AM   #1
jasonburt
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Wink All LS400 owners with bad gas mileage READ THIS!

My gas mileage on my 1991 LS400 was averaging 16 miles to the gallon. I had replaced oxygen sensors,wires,plugs,cap,rotors,thermostat,throttle body cleaning with no improvement. After studing ECU theory, I found out the Coolant Tempurature Sensor is the "MAIN SENSOR" for the computer. This sensor has more control over the computer than any other sensor. To make a long story short, my COOLANT SENSOR was telling the computer it was -20 degrees farenheit(thats minus 20 degrees) and no check engine light. Cost of new sensor was 50 dollars. I now get 23 miles to the gallon higway with a light foot. I now save 650 dollars a year in gas driving 12000 miles a year and I can feel the 250 horsepower when I open it up. If you have an old LS400...CHANGE THIS SENSOR!!
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Old 08-31-08, 01:00 AM   #2
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wheres the sensor at?
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Old 08-31-08, 01:07 AM   #3
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The Coolant tempurature is located on the front left top of the motor. you have to remove the all the plastic pieces from the top front of the motor. The far left is the coolant temp sensor...to the right of that sensor is the one wire temp sensor for the tempurature guage. There is a large sensor around these 2 sensors screwed in an angle from the front of the coolant jacket...this is the thermal time switch.
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Old 08-31-08, 02:49 AM   #4
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When you change the ECU tempurature sensor you must reset the computer by pulling the ECU fuse for a minute, then replace it.
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Old 08-31-08, 06:35 AM   #5
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I had the same with my Chevy, replacing it worked well indeed
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Old 09-01-08, 11:31 AM   #6
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What does the temperature sensor look like?

Where did you buy it?

I found something at Autozone, but it looks like the one that goes into the radiator.
Click the image to open in full size.
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Old 09-01-08, 03:03 PM   #7
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+1 on more info on where to buy
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Old 09-01-08, 07:32 PM   #8
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Quote:
Originally Posted by jasonburt View Post
My gas mileage on my 1991 LS400 was averaging 16 miles to the gallon. I had replaced oxygen sensors,wires,plugs,cap,rotors,thermostat,throttle body cleaning with no improvement. After studing ECU theory, I found out the Coolant Tempurature Sensor is the "MAIN SENSOR" for the computer. This sensor has more control over the computer than any other sensor. To make a long story short, my COOLANT SENSOR was telling the computer it was -20 degrees farenheit(thats minus 20 degrees) and no check engine light. Cost of new sensor was 50 dollars. I now get 23 miles to the gallon higway with a light foot. I now save 650 dollars a year in gas driving 12000 miles a year and I can feel the 250 horsepower when I open it up. If you have an old LS400...CHANGE THIS SENSOR!!
what about 98 LS400? where is the coolant temp. sensor located? And how do you determine the sensor is bad? Thanks.

Last edited by lexie; 09-02-08 at 02:00 AM..
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Old 09-02-08, 07:18 AM   #9
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Avalon, that is the correct sensor. For the cost of the sensor...just replace it. testing the sensor is cumbersome and a bad sensor won't even set off the check engine light. Your engine will run really rich and you will barely pass emissions testing. This sensor should be changed with every tune-up in my opinion. Looking around the net, alot of information about these sensors becoming sluggish when they get older.
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Old 09-02-08, 07:22 AM   #10
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Avalon, I bought the sensor from the toyota dealer. Get the part number from Lexus and give it to your local Toyota dealer. You will save 15-20 dollars on the part. The part number is common to most toyotas and lexus's.
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Old 09-02-08, 10:47 AM   #11
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8942220010 $59.13 (retail) $40.88 (discount)
Electrical - Powertrain control - Coolant temp sensor...LS400 1990 - 1994

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Old 09-02-08, 12:24 PM   #12
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Bradster,

Nice work. Part #'s are always helpful.
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Old 09-02-08, 09:47 PM   #13
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here is how to check if your (engine coolant temp) ECT sensor is good or bad
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File Type: pdf Engine Coolant Temparature Sensor check.pdf (150.4 KB, 3892 views)
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Old 09-03-08, 01:18 AM   #14
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This test is not completely trustworthy. The ECT sensor operates dynamically like an oxygen sensor. This is a static test. It does not tell you how fast the sensor reacts to changes in tempurature. As these sensors age they may take 30 minutes to tell the computer your engine is hot..or may not ever tell the computer your engine is hot at all. This sensor is like an oven thermometer..it's trapped in all the heat under those engine covers and when it bakes over the years it becomes flaky, just like the thermometer in your oven, in your house. I'm going to look into the EGR temperature sensor as well.
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Old 09-03-08, 09:49 AM   #15
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ok, dumb question here, but i thought that the coolant temperature is what is read on the dash gauge as temp? So, if the coolant temp sensor was showing that cold, the dash gauge would show cold the entire time operating the car? Or, is that temp gauge signaled by the thermostat?
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Old 09-03-08, 09:49 AM
 
 
 
 
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