The heater hoses.
the coolant is contaminated with fission productsif the coolant is water and the fuel pellets are canned in zirconium a chemical reaction may occur that could generate large amounts of hydrogen gasif enough core is exposed without coolant, the molten core material could melt through the reaction vessel and eventually the floor of the containment building (this is very unlikely unless there was a severe loss of coolant accident and the emergency coolant system was disabled)
Could be a failing fuel pump.
If the coolant reservoir can not maintain the proper level of coolant, it is possible the engine could over heat when the level drops.
The coolant sensor moniters the coolant temperature. A faulty thermostat could cause the engine to run cool.
The coolant leak is pretty cut and dry - you have a leak somewhere. The lukewarm heat (assuming you're referring to the car's heater) could be for a number of reasons. Insufficient coolant could be one of those. Your coolant could be burnt out. It could be a problem with one of your heater hoses. You could have a worn out heater core.
There are several reasons why a 1996 Achieva engine cranks but will not fire. A few of the reasons could be a bad ignition control module, ignition coil pack, or a crankshaft position sensor.
The coolant temp. sensor could be bad....or the thermostat could be stuck shut.....there are a few things it could be actually
It lowers the boiling point of the coolant It could allow air into the system It could prevent proper coolant circulation
its for sure a blowed head gasket or intake gasket
If coolant level is correct - could be a defective sensor
If coolant full could be a bad sensor
The new sensor could be stuck. Or the wiring could be loose, or the coolant could actually be low. Check the coolant level and the sensor wiring first.