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Coolant Temperature Gauge Doesn't Work.


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My coolant temperature gauge doesn't work. The needle went down very slowly over the course of couple of years. Now it stays at the lowest level and won't move.

What should I do? Replacing with a new gauge or replacing some capacitors or something else? (It's a 1990 L'S 400 with 432000 miles).

Please help. Thanks

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Well, you will need to determine if the gauge is telling the truth. It could be that your thermostat slowly stayed open and you really are running with a cool engine. Or your gauge could be faulty or bad temp sensor.

With 432k miles, it could be any of those. It might help to know some history like the last time coolant was changed, thermostat changed..etc.

Do you get hot (not just warm) air from the heater when running?

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At about 400k miles, I had timing belt changed. At that time the gauge was already dead but I went ahead to change thermostat, water pump, engine coolant temperature sensor and the sending unit. And all that didn't help at all. My heater works just fine. The engine runs good. Everything looks fine. Gas mileage good too. Engine temperature behave very good. I don't lose coolant at all. I got a feeling that maybe the instrument cluster corresponding capacitors gradually went bad because the needle going down very slowly over a period of 2 years or so. If so, then what capacitors are bad that need to be replaced?

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  • 2 weeks later...

I don't know if it's worth it to you but I would def look into rebuilding the cluster since that seems to be a common issue with these cars.

I would verify if the circuit is still good before building the cluster. Since all parts have been replaced and are good, next step should be troubleshooting.

If you remove the cable connected to the coolant temperature sensor and short that circuit (or at the ECM itself), the temperature should jump to High for HOT. If it is not --> the problem maybe with the circuit (or the ECM).

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