Do a search for your ects sensor. I am trying to find out how many temp gauge sensors are on the car right now myself. I am having the same problem. I am going to change the temp gauge sensor(s) and thermostat and flush the radiator.
Low Coolant Level.There is not enough coolant in the reservoir.
There is a sensor valve located inside the reservoir its may be bad
The extra coolant will simply be pushed into the reservoir once the coolant heats up enough. It is also possible that (especially if there is already some fluid in the reservoir) that it will be pushed out of the reservoir unto the ground. Radiator fluid (antifreeze) is toxic to animals (it tastes sweet and so animals may be attracted to it). Please clean up or spray down with plenty of water any coolant that leaks or pours on the ground.
It might be clogged, thus not allowing enough flow It means that the excess coolant is going where it is supposed to. The coolant expands when hot and goes to the over flow reservoir.
You have reinstall the head gasket. It has been not tighten enough or damaged. Anyway the replacement was not done properly.
When the low coolant warning light comes on and the car has enough coolant, it usually means there is a problem with the coolant level sensor system. The sensor may need to be replaced.
There are two possibilities here:The coolant is frozen (not enough coolant was present, too much water was present, or the temperature dropped low enough to freeze the coolant).Some coolants are not meant to be mixed. I've heard it told that doing so with the wrong coolants can result in solids being formed. I've never seen it, but if this is the case, you should not run this sludge through your engine--that is unless you want to rebuild your engine.
You shouldn't need perform any special tasks to get the air out of the cooling system. Just fill the radiator as much as you can (if you can open the radiator that is, some vehicles don't have a radiator cap) then fill the coolant reservoir to the "cold" mark and run the engine long enough to get the heat up a bit. That will cause any air to expand and push out through the overflow. Turn off the engine, let it thoroughly cool and that should pull in coolant from the reservoir. After the engine has cooled, check the reservoir and add coolant as necessary to bring it up to level. Repeat that process a few times over the next few days and you should eventually get to the point that you're not needing to add more coolant to the reservoir. At that point, the air should be out.
It sounds like you may need to replace your thermostat. Even though you have enough coolant in the radiator and overflow reservoir the coolant may not be circulating through the system because the thermostat is not opening. When the coolant can't flow through the engine and radiator it will get very hot and stay very hot. This is usually an inexpensive and fairly easy fix, just purchase a new thermostat and install it or have a mechanic do it for you.
It depends on what you mean by going off and on. If it happens like a flashing light (check engine) It will not be low coolant. It usually mean that you have a random missfire and that it is bad enough of a missfire that it is damaging your catalytic converter. You need to get to an auto parts store that will check your trouble codes.
== == Sometimes it is not actually "boiling", but bubbling. Start by getting a new radiator cap. It is the first thing you should do, and is easy. *MAKE SURE YOUR CAR IS NOT HOT WHEN REMOVING A RADIATOR CAP* When air enters the closed/pressurized cooling system, the air ends up in your reservoir tank and bubbles the top. Sometimes(depending on vehicle) it will even exit the reservoir tank through an overflow hose and appear to be a leak. Hope this helps! Chris not enough water or coolant in radiator.
Not Unless You Allow Enough Coolant Loss To Overheat Engine. If Your Reservoir Isn`t Leaking Too Bad Keep A Watch On Your Water Level You Will Be OK. But If You Have Decent Weather You Can Remove The Reservoir, Clean It Up. At a Parts House Buy A Two Part Epoxy (clear) Apply It To The Hole Or Crack On The Tank Allow It To Dry. Put It Back On Good As New. GOOD LUCK