Olds 98 Low Coolant Warning

[Justpassingthrough]

I've got a 1984 Olds 98 Regency and I recently replaced the thermostat and thermostat housing (housing was leaking). Everything appeared to be working fine after I put it back together but now the low coolant light and buzzer is coming on continuously. Coolant level is fine and I've pulled the "gages" fuse to shut the buzzer off. My question is, where is the sensor located, how does it work and what might be causing it to run continously?

[1968 Pontiac]

Coolant level sensor should be below the rad cap between the tranny lines on your rad.

When I do this type of repair/maintenance, I leave the rad cap off until the thermostat opens and sucks the coolant through the engine. Then with the car running and coolant circulating, I top off until the rad is full, then install the cap. All this while the car is running, fully warmed up and the heater on full blast.

[80sOlds98]

If you replaced the thermostat you must have drained some coolant. When your coolant is dirty and the sensor gets exposed to air, gunk coats the sensor and it fails to ground properly. This causes the low coolant indicator to "stick" on.

It's not an expensive item, so I would just go ahead and replace it.

Also check all your ground straps, especially the engine ground strap. Faulty grounds can cause all kinds of problems and your car's electrical system is getting really old!

Hope that helps!

BTW, the sensor is located so the indicator goes off only when the radiator is half empty! This is way too long to wait for a warning. When I had my car, I relocated the sensor to the coolant reservoir.

First I cut a small hole in the top of the coolant reservoir. Into this I placed a piece of black 12 gauge wire to act as a ground. The wire was fed down into the coolant and the end stripped about 1/2-inch so the wire was exposed. I used a strain relief to secure the wire in the hole at the top of the tank and the other end of the wire was bolted to the fender.

Next I used a piece of brake line and some fittings to make a custom sensor probe. The length of the probe determines the time when the warning goes off. I placed it so the probe would be out of the coolant when it reached the "low" mark on the bottle. The top of the probe was connected to the sensor wire leading to the reminder module usine an eyelet threaded onto the fitting with a nut.

There were two problems with this approach:

1) The warning would sometimes go off when I went around corners and the coolant swished around in the bottle. As soon as the probe met air, the warning would trip! So be sure to make the probe long enough that it will stay in the coolant until the bottle is practically empty. With this approach you will have a warning before your coolant is practically gone!

2) With dirty coolant, as soon as the probe met the air some gunk dried on it and prevented the circuit from being completed. So if the coolant got low enough to trip the warning it would sometimes "stick" on. It became necessary to clean the probe and ground wire after the warning was tripped when the coolant was really dirty. But at least this was easy with the probe in the bottle rather than the radiator. If I had used stainless brake line, I don't think this would have been a problem.

Later I upgraded my design. First I tried routing the ground wire down inside the brake line so both wires were in one assembly. You must make sure the wire goes down far enough so the exposed end can't contact the probe. Later I just used two probes -- one hooked to ground and the other acting as a "positive" hooked to the sensor circuit.

This saved my engine. At 120K miles, my intake manifold gasket blew while I was on the freeway and coolant started pouring out of the top of my engine. Since my custom warning went off early, I had time to pull over before I lost all my coolant! No harm done, a tow to my mechanic and I was back on the road in a couple of days.