90 coolant temp sensors - need clarification
Thread Starter
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Joined: Nov 2007
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From: VN
90 coolant temp sensors - need clarification
guys, I replaced coolant temp sensor, temp sender and and found out that my car has 4 sensors/ switches related to coolant. please see image below taken from my car
I believe marked as 1 is temp sensor (send data to ECU), 2 is temp sender for temp gauge in comb. cluster, I dont know 3 and 4
I believe 3 is a switch, not sensor. it will switch on/off when coolant temp reach certain temp. I have no idea about 4, but 4 was broken long time ago, car is still running fine.
I bought another housing from 91-92, but it does not have holes for sensor 3 and 4 so I have not replaced yet. I tried unplug wire to switch 3 and run the car from cold. it seems work as normal. car started at 1000-1100rpm, and went down to 800 when working temp was reached after 5-10 minutes.
My question is: what the switch 3 is for and if I can just delete it? 4 is not important to me but any information about it will be appreciated.
I believe marked as 1 is temp sensor (send data to ECU), 2 is temp sender for temp gauge in comb. cluster, I dont know 3 and 4
I believe 3 is a switch, not sensor. it will switch on/off when coolant temp reach certain temp. I have no idea about 4, but 4 was broken long time ago, car is still running fine.
I bought another housing from 91-92, but it does not have holes for sensor 3 and 4 so I have not replaced yet. I tried unplug wire to switch 3 and run the car from cold. it seems work as normal. car started at 1000-1100rpm, and went down to 800 when working temp was reached after 5-10 minutes.
My question is: what the switch 3 is for and if I can just delete it? 4 is not important to me but any information about it will be appreciated.
Last edited by qha_vn; Mar 9, 2014 at 08:07 PM.
Lexus Champion
Joined: Dec 2011
Posts: 4,078
Likes: 87
From: Birmingham, AL
you are correct on the functions of #1 and #2 
definitely replace #1 - it looks nasty and is likely 20 years old! - and it is the important one - is less than $50 at Sewell - should improve fuel economy and performance noticeably! p/n 89422-20010
I thought you already replaced it?
#3 is the START INJECTOR TIME SWITCH p/n 89462-20020
#4 - I will remember once I have had my coffee!
definitely replace #1 - it looks nasty and is likely 20 years old! - and it is the important one - is less than $50 at Sewell - should improve fuel economy and performance noticeably! p/n 89422-20010
I thought you already replaced it?
#3 is the START INJECTOR TIME SWITCH p/n 89462-20020
#4 - I will remember once I have had my coffee!
Last edited by LScowboyLS; Mar 9, 2014 at 09:11 PM.
Thread Starter
Pole Position
Joined: Nov 2007
Posts: 324
Likes: 0
From: VN
you are correct on the functions of #1 and #2
definitely replace #1 - it looks nasty and is likely 20 years old! - and it is the important one - is less than $50 at Sewell - should improve fuel economy and performance noticeably! p/n 89422-20010
I thought you already replaced it?
#3 is the START INJECTOR TIME SWITCH p/n 89462-20020
#4 - I will remember once I have had my coffee!
definitely replace #1 - it looks nasty and is likely 20 years old! - and it is the important one - is less than $50 at Sewell - should improve fuel economy and performance noticeably! p/n 89422-20010
I thought you already replaced it?
#3 is the START INJECTOR TIME SWITCH p/n 89462-20020
#4 - I will remember once I have had my coffee!
what is the START INJECTOR TIME SWITCH for? the car can run with it unplugged. thanks
Driver School Candidate
Joined: Sep 2013
Posts: 14
Likes: 1
From: Utah
I too have a number 4 issue I believe. Its the sensor on the coolant front cross bar with two vacuum hoses, near the top radiator hose, in need of repair. What does it do and whats the part number? I'm getting the message from LSCowboy to replace the temp sensor under the plug wires - right side. But still concerned about #4 in your pic.
Lexus Champion
Joined: Dec 2011
Posts: 4,078
Likes: 87
From: Birmingham, AL
Driver School Candidate
Joined: Sep 2013
Posts: 14
Likes: 1
From: Utah
What was #4 called and what did it do? Should a 1990 LS400 owner worry about it? (BTW - I will replace the temp sensor - after I replace the steering column gear.)
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Thread Starter
Pole Position
Joined: Nov 2007
Posts: 324
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From: VN
dont know what #3 and 4 are for. my car however appears to run fine without #4 for years. I am going to unplug #3 to see if there is difference. if not see anything harm, will delete it as well as I have a 93 housing.
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If those four are not enough, there is one more coolant temp. sensor at the bottom of the radiator, driver side. it sends a signal to turn on the fans if the coolant temperature gets too high. A lot of people neglect that one as it is almost never needed (unless you live in a hot place), due to LS400 cooling system being way overbuilt, but you can only cook your engine once...
