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"Low" coolant sensor testing

9K views 7 replies 3 participants last post by  marlin1881 
#1 · (Edited)
I searched a while for this but couldn't find a way to test the coolant sensor to make sure it illuminates when fluid is low. I noticed that my fluid was just a bit low in the ET and I wanted to make sure the light would illuminate when a true low-fluid situation occurs.

- I did test the entire set of dash lights and the little yellow radiator does illuminate, so I know that the radiator dash light works.

- But, when pushing the float stick down to the bottom of the ET until it stops, the radiator light does NOT illuminate. Should it in that condition? How low does the fluid need to be before the light comes on?

- In checking the owners manual, when turning the key to position 2, the radiator light is NOT one of the lights that turns ON/OFF with the others, like the oil or battery light.

Is there a way to test this? Sorry if this has been answered before, but I saw a lot of threads on how to turn this light OFF. I'm asking about the opposite.

Thanks.
 
#3 ·
Wow! Thanks for the link. And, it is interesting to see how the first theory was eventually disproved, and a second theory was under discussion.

I'm still not sure how to actually test the condition to forcefully activate a low-coolant condition to where the dash light should turn on.
 
#4 · (Edited)
OK. An update on forcing the low-coolant light condition:

- Just disconnect the sensor wire plug at the bottom of the tank. Here's the key, though. You have to wait 30 seconds for the dash light to come ON. I was way too fast with my earlier testing. When you disconnect the sensor wire plug, and just leave it dangling, the light will come on at the dash, in 30 seconds. This will validate whether your wire plug is working or not.

- Twist the sensor to remove it from the tank. Be careful with the sensor probe as it is quite delicate. Connect the sensor wire plug, leave the assembly dangling, and observe the dash light for 30 seconds. The light should still be ON. This will validate whether the sensor is working at some level, or not.

- Replace the sensor in the tank and connect the plug wire. If you have proper coolant level, the dash light should go out, in 30 seconds.

Now, for my car, here's where it gets questionable. I siphoned all the ET fluid out to where the float stick could only move down 1/4" before hitting bottom, as I couldn't get under the float to have it completely dry. Even in this condition, my dash light would not illuminate.

So, this leads me to believe that there is a fault in my tank, somewhere in the manufacture of the area around the magnet? Thoughts? I have an old tank in my parts stash so I'm trying figure out a way to test it without removing my current tank. Not much room down there and the plug wire doesn't have any extra length to it.
 
#5 ·
So, I've now tested 2 tanks and 2 sensors. Same reaction in both cases. The only thing I haven't been able to do is to force the low-coolant light when the sensor is in the tank.

For my latest testing, the current tank is installed in the car and I siphoned off all the tank fluid, with the float stick at the bottom of the tank. My old tank (which was working fine when I replaced my cooling system) was hooked up to the wire plug, while hanging suspended upside down. I pushed the float stick to the bottom and watched the dash for 1 minute. Dash light did not come on.

I'm at a loss on how to simulate a low-coolant situation. I'm open to ideas.

Thanks.
 
#6 ·
I searched some more (about 4 hours worth, on various sites), and learned that there is a reed switch that is affected by the magnet in the ET. So, I took out my sensor and looked at it under a 10X glass. Yep, there is a "switch" in the glass bulb, and I was able to force it to close by using a magnet. The amount of movement is finer 'n a frogs hair, tho... It does open and close the circuit.

But, I still can't force the condition to happen when the sensor is in the tank... Still open to ideas here. I want to make sure when there is a low coolant condition, that my dash light actually turns ON.
 
#8 ·
The only way I was able to force the low coolant condition, is to drain the ET (expansion tank). Once the float stick was at the bottom of the tank, and 30 seconds had elapsed, the dash light came on. It's easy to do, if you want to give it a try, as there's really not much fluid in the ET itself. Make sure you drain into a clean pan and then pour it back into the tank.

I'm still not sure why holding down the float stick, with fluid in the tank, didn't work...
 
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