Originally Posted by swebster@myrvadvanta
another thought on this. My light came on unexpectedly once on a long trip. I pulled over, checked the coolant level and it was fine. A few more miles and the light went off...then on then off. It turned out to be a loose connection on one of the wires to the coolant resevior. A quick re-crimp and it works fine now.
I have to agree with you on this one, but I still think there are a couple of holes in this "low fluid" argument.
You stated earlier that your "low coolant" light came on when your aux heater line blew. If the engine was loosing coolant, I can't conceive a scenario that would explain how the external coolant reservoir was "sucked dry" while the engine was running. I would imagine that as the engine lost coolant, and continued to heat up, it (the hot engine) would continue to "boil" the coolant, causing even more pressure, and eventually emptying the active system of fluid, but maintaining pressure until the very end, which would preclude the external reservoir from being sucked "dry". The engine and radiator would have to be in a "vaccuum" situation to pull the coolant into the active system from the external reservoir.
Now, my external reservoir does not have electrical contacts, the windshield washer fluid reservoir does, but not the coolant reservoir. Of course, my expansion reservoir could very well not be stock.
I had always assumed that there was a "float" with contacts near the top of the radiator that would indicate actual fluid level in the radiator itself (I thought I had heard this in an old thread). I searched my radiator, and the only electrical contact on the radiator that I can find is near the bottom back, curbside, between the radiator drain and the transmission fluid inlet line, and I believe that that electric contact is a thermostatic switch for the electric air fans.
So, to summize, my radiator does not appear to be equipped with a "float" switch to indicate low radiator coolant level. And, if the contacts in the external expansion tank activate the "low coolant" light, how did your aux heater leak empty the expansion tank while the engine was running (and maintaining a positive pressure in the cooing system).
One good thing, this thread precipitated a thorough inspection of the front section of the engine compartment. I found the #2 electric cable from the charge splitter to the battery compartment partially severed by the Air Conditioner Compressor drive pulley. One minor catastrophy averted.
Any other thoughts on how the "low coolant" light is activated?