4AGE Water temp sender. How to troubleshoot

[Howieau]

Hey,

The water temperature gauge in my AE82 4AGE corolla(standard-bluetop) is not reading correctly. It shows the temp to be almost on completely cold when the engine is obviously warmed up. I want to test the water temp sender sensor before I go ahead and purchase another. I believe there is a way to do this by checking the voltage output of the pins on the water temp sender sensor, yet I am unable to find what sort of voltage it should be putting out, thats even if thats the right way to check it.

Does anybody have access to the workshop manual for this model and could perhaps scan those couple of pages referring to trouble shooting the water temp sender sensor? Or even if anyone knows how to test it to see if its functioning properly, please let me know it would be much appreciated.

Thanks in advance

[oldcorollas]

the sensor is a veraible resistor (basically.. i forget the proper name)
the ECU or gauge provides a voltage to the sensor, and the sensor grounds that voltage via it's resistance

if you measure between the connecotr and the engine/battery, you will see the resistance change with temp

perhaps the bit that sticks in the water is covered in crud?

[Bazooka]

Taken from the AE86 manual;

Using an ohmmeter, measure the resistance between the terminal and ground.
If each resistance value is not as shown, replace the sender gauge.

Water Temp Resistance (ohms)
50deg C 226 +33.6 -36.6
115deg C 26.4 +1.71 -2.21

AW11 manual is the same but states a difference of -33.6 at 50 deg C

[JoJo]

Have you thought about the thermostat?
If it is stuck open, the gauge may actually be reading right.

Thats cheap and easy, check that........

It may feel warm to you, but you cant tell the differance between 50deg and 87deg with your human sensors. The optimal running temp is 87deg (normal/middle of gauge) and if it's only 50-65deg, it shows cold on the gauge....

[the_random_hero]

Same thing in my AW11, I'm fairly sure it's the thermostat - I have bought new coolant/water temp sensors just in case it isn't.

[Howieau]

I pulled the water temp sender out of the block and cleaned the end of it where it sits in the coolant. No change.

I cleaned up the other end of it and the inside of the plug that connects to it, no change.

I used a multimeter set on resistance and tested it. When the car was warmed up and the coolant was at 80*, it read -54. Is this a sure sign that its defective, seeing as it is giving negative resistance values? When I have it set to resistance on the multimeter and I have holding the two probes away from each in the air, it reads 1 (100% resistance I presume), and when I connect the two probes together it reads 1.3 ohms.

Does it sound like my multimeter is reading correctly, and the water temp sender is defective?

Also, I am unsure how the thermostat will affect the water temp gauge reading. If it was stuck open it would take a long time for the car to warm up but it would still eventually warm up after a while and therefore show a correct reading on the gauge. If it was stuck shut the car would overheat. Am I missing something?

Cheers

[JoJo]

Also, I am unsure how the thermostat will affect the water temp gauge reading. If it was stuck open it would take a long time for the car to warm up but it would still eventually warm up after a while and therefore show a correct reading on the gauge. If it was stuck shut the car would overheat. Am I missing something?

Cheers

Yes, you're missing something........ With no thermostat, it DOESN'T reach the correct operating tempreture.

My 4AGTE runs at 53deg without thermostat and 87deg with thermostat. Running it longer doesn't mean the temp gets hotter.

How are you testing the water temp? (the 80deg you stated)

[Howieau]

I ran the car for a while idling to let it warm up, then tested the water temp sender then quickly turned the car off, opened the radiator cap slowly with a towel until all the pressure was released, and then put a temperature probe in the coolant.

[KARNAGE]

mate a new temp sensor are cheap as well i picked my last one up for the aw11 for 22 dollars

[Howieau]

Sounds cool I just dont want to buy one yet until I know that I need to.

[JoJo]

mate a new temp sensor are cheap as well i picked my last one up for the aw11 for 22 dollars

You might aswell do this, they are cheap...

[senn]

Generally the thermostats don't jam open, they jam closed, or at least the ones in my old ae82 used to, until i got sick of changing them every 3-6 months...(never worked that one out)
cut the guts out and made a restrictor plate, which was fine in summer, but come winter it couldn't maintain temperature on cold nights.

[KARNAGE]

i know a few mates that run big power v8 engines and turbo engines, that run with the no thermostat at all, and they work well. From my experience if its saying its running cold when obviously it should be warm it was the the temp sensor causing the problems.