qha_vn

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.

LScowboyLS

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!

qha_vn

yes I did, this pix had been taken before new one sit in.

what is the START INJECTOR TIME SWITCH for? the car can run with it unplugged. thanks

Skyhawk474

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.

qha_vn

I have no idea about #3 and 4. I got 93-94 repair manual (they told me 89-94 when I bought it) which mentions nothing about those 2 switches/sensors

LScowboyLS

#3 and #4 were phased out before 1993, that is why they are no longer in the manual

#2 was phased out for 1998

Skyhawk474

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.)

qha_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.

peterls

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...

Skyhawk474

Thanks guys - but sensor #4 remains a mystery!

qha_vn

#3 and #4 to be exact

LScowboyLS

#3 is the START INJECTOR TIME SWITCH p/n 89462-20020

qha_vn

I mean what it is for and wether can be deleted is still mystery

qha_vn

I unplugged #3 sensor yesterday morning. there appears no difference. engine runs as before from cold start or warm start.

I am happy to remove it permanently

Skyhawk474

And #4? Has something to do when the engine reaches a certain temperature. For what purpose - Dunno, fuel economy? idle speed? (non electrical too. But one vacuum line goes to the air box)