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How do I tell if my coolant level sensor is bad?

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Old 12-13-18, 11:40 PM
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How do I tell if my coolant level sensor is bad?

So I drained some antifreeze to change the fans out, not all of it but maybe a liter or so. And then I put back in the exact amount I took out because I was able to save it. So fast fwd I got everything back together and then I started it and the add coolant light/buzzer is on. I searched for a solution and I mainly got “get the no spill funnel” which I indeed purchased said funnel. Used that, didn’t get much of anything from that, I let it set 1/3 of the way full over night, and the next morning it was gone, but my overflow tank was now 3/4 the way full so that’s where that went. So I decided to take it for a drive even tho the buzzer was going off. The whole time temp gauge hovered below the half way mark. And I had the heat on the whole way and it was blowing warm, not hot, air. Oh and when I started it, the buzzer was on without a light (weird) and then they both went off, 5min into my drive they both came back on and haven’t shut off again. Anyone have any ideas?
Old 12-14-18, 07:45 AM
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Did you open the filler cap afterwards to ensure the coolant is still topped off? Here is a good thread pertaining the sensor, from the FAQ thread: https://www.rx7club.com/3rd-generati...thread-995956/

I would highly suggest getting an aftermarket temp gauge so you can see exactly what temps you're running. If you've researched the factory gauge, you will know it has a huge range before it moves. I have the power fc showing my temp at all times in addition to an aftermarket gauge probed into the radiator hose.
Old 12-14-18, 08:21 AM
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Oh boy that sounds like a pain lol I appreciate the link! I may have to troubleshoot along that route here soon
Old 12-14-18, 08:45 AM
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Most likely you just have air at the top of the thermostat housing. The coolant level sensor is a super basic circuit, if the wire is connected and hasn't snapped off the sensor is probably good.

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Old 12-14-18, 10:35 AM
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I recently replaced my coolant level sensor due to intermittent false warning lights even after repeated bleeding with the Lisle funnel. There is a diagnostic procedure in the manual for the sensor but it can be a tricky/intermittent thing. My advice is: everything electrical on a 25 year old car is suspect. Just replace it. The damn thing was driving me nuts, coming on unpredictably.
Old 12-14-18, 01:17 PM
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I was trying to avoid spending 80$ for a new one lol gotta do what u gotta do tho! Is it normal that the overflow started filling up as my lisle filter was left 1/3rd the way full over night? I was thinking a possible stuck thermostat, but I could be completely wrong
Old 12-14-18, 03:23 PM
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You need to do some basic troubleshooting on the coolant system - no leaks in the overflow hose, radiator cap good, etc. Also be certain the caps aren't switched if you have an AST.

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Old 12-14-18, 03:49 PM
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Originally Posted by ecurbd02
I was trying to avoid spending 80$ for a new one lol gotta do what u gotta do tho! Is it normal that the overflow started filling up as my lisle filter was left 1/3rd the way full over night? I was thinking a possible stuck thermostat, but I could be completely wrong
The overflow bottle should not gain volume if you have a functioning pressure cap on your AST, and you are doing the filling at the engine thermostat housing fill point. The AST pressure cap should prevent passage of coolant to the overflow bottle, regardless of how much coolant is in the funnel. Note that the thermostat housing cap is not a pressure cap, just a "blank" cap to seal the opening.
Old 12-14-18, 04:53 PM
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Originally Posted by jza80
The overflow bottle should not gain volume if you have a functioning pressure cap on your AST, and you are doing the filling at the engine thermostat housing fill point. The AST pressure cap should prevent passage of coolant to the overflow bottle, regardless of how much coolant is in the funnel. Note that the thermostat housing cap is not a pressure cap, just a "blank" cap to seal the opening.
Hm maybe I don’t have a working one, I never thought of that. I was filling at the thermostat housing. Can I clean and fix the ast cap or would I need a new one?
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