Coolant warning light

[Radical Racing]

The coolant warning lights (located on the rectangular panel to the left of the steering column) on both my '88 and '89 635 Csi will not turn off. I replaced the sensor/float that screws into the radiator overflow tank with new parts. I cleaned the contacts on the two wire plug going to the sensor and checked for breaks in the wires. Coolant level was filled to recommended line. Lights stay on even after I hit the check button.

Can anyone tell me what I should do to check the voltage to the contacts and what the readings should be? And anything else I should check.

On the '88, if I overfill the overflow tank the warning light will not come on but after a short drive it comes on and the coolant level is back down to the recommended level.

Thanks in advance for any assistance.

[baders]

Sounds like your Active Check Control module may be faulty. To test, disconnect the Brown/Blue wire on the coolant level switch and ground this wire out. If the light stays on you have a faulty ACCM or an open circuit on the brown/blue wire to it. You could then ground out pin 18 on the ACCM to further check.

[raykoke]

Bridge the 2 leads at the sensor connection. If the lights go off, the sensors are bad. If not... it may be something else

GL,

Ray

[Radical Racing]

When I filled the overflow tank to the very top the check light went out. A day later it came on again. When I checked the level in the overflow tank it was very low and the float on the sensor shaft was as low as it could go and not floating. So either I have a cooling system leak (which I see no sign of whatsoever) or possibly a weak radiator cap that is allowing too much coolant out when hot. When I bought the car used it came with a Stant 16 lb. cap with the red lever pressure release feature. Should I use a different brand of cap and/or pressure?

Thanks in advance for any assistance.

[raykoke]

When I filled the overflow tank to the very top the check light went out. A day later it came on again. When I checked the level in the overflow tank it was very low and the float on the sensor shaft was as low as it could go and not floating. So either I have a cooling system leak (which I see no sign of whatsoever) or possibly a weak radiator cap that is allowing too much coolant out when hot. When I bought the car used it came with a Stant 16 lb. cap with the red lever pressure release feature. Should I use a different brand of cap and/or pressure?

Thanks in advance for any assistance.

Well I think that's the least expensive potential solution.

You can check for a bad head gasket later.

:)

[Radical Racing]

I've doubled checked both cars ('88 and '89 635 Csi auto). The coolant warning light goes out when I fill the overflow tanks to the top.but comes back on later. When I check the coolant level it has gone down below the recommended level to the point where the float on the sensor is bottomed out and not floating. No sign anywhere of coolant leaks and no sign whatsoever of a leaking head gasket i.e. mineral stains or a cream like deposit near oil filler cap or overheating. So I can only conclude that the coolant is flowing out the overflow tank hose. Seems like means a weak radiator cap. I can't find any reference to what pressure a new cap can be. Can anyone give me a spec?

Would a faulty thermostat have this effect? Neither car is overheating so doubt it is a thermostat problem but needed to ask any way.

Thanks in advance for any assistance.

[hornhospital]

The cap should be 1.0 bar (15 psi). An easy way to confirm the coolant is going out the overflow is to put a catch can/jug on it, fill up the expansion tank, and take it for a drive.