Not a sensor, it is a heater for the coolant, that wire will run to the front grill area and have a 110voltAC plug on it, on cold days, below freezing, you would plug this in to your house electrical and it would preheat the coolant so when you did need to go somewhere the engine wouldn't take as long to warm up.
If you have never used this, which it sounds like, then you don't need it.
Best fix is to remove the rusted expansion plug and replace it with a rubber expansion plug.
Any auto parts store sells them.
You need the old plug to get the correct size or the engine model number and location of the old plug and the auto parts store can look up the size.
The rubber ones won't rust, and are easily installed and removed if you ever want to replace the "block heater" with a new one.
The common term for these plugs is "freeze plug" but that's an old wives tail name, lol, one mechanic years and years ago told a gullible customer that these plugs were there to pop out and save the block in case it froze, rotflmao.
yeh, right, there is no doubt that they would, and do, pop out if water or coolant in the block freezes, seen it myself, but it wouldn't, and in one case for sure, didn't save the block.
The holes are there to remove the sand after the block is cast from molten metal, they are "casting holes", plugs are put in the holes to seal them, metal expansion plugs is the cheapest way to do it.
Rubber plugs are better but cost a bit more, and the metal ones can last the life of the engine, so they are not "bad", but on occasion they can rust out if coolant wasn't change quite as often as it should have been.
Last edited by RonD; 08-05-2014 at 01:30 PM.