Engine overheating, 2000 deville
The problem is that more heat is entering the water than is being extracted by the radiator.
But there can be a lot of causes for that. If you have a head gasket leak, it can introduce hot gasses into the water, increasing the heat load while raising the pressure in the cooling system. That in turn can push water out of the cooling system, and into the recovery reservoir, where it can't help with the cooling of the engine.
If the fins of the radiator are blocked or folded over, that part of the radiator will not contribute much to the cooling.
If the internal water passages of the radiator are blocked, the area of the radiator is effectively reduced.
A worn out bottom radiator hose can collapse from the suction of the water pump, blocking the water flow.
If the fuel mixture is too lean (not enough fuel in the given volume of air) the engine will generate quite a bit more heat, possibly overwhelming the system.
When the engine is cold, the thermostat (a valve in the hose where water exits the engine to go to the radiator) is closed. This prevents water from going to the radiator, and that in turn prevents water coming from the radiator to the engine.
Water instead leaves the engine through the heater hose near the upper radiator hose, and circulates right back to the inlet of the water pump. So the water circulated through the engine, but it has no way to shed any heat it picks up. This speeds up the warm-up process.
The water circulating this way passes by the back of the thermostat, causing the thermostat to warm up along with the water.
When the thermostat reaches its opening temperature, it starts to open, allowing some water to go out of the upper hose to the radiator, and therefore some water from the radiator to enter the engine.
Right away, the water in the engine falls below the opening temperature of the thermostat and it closes.
The newly cooled water gets warmed by the engine, raising it to the opening temperature of the thermostat, and the whole process begins again. But this time, the water coming from the radiator is just a little warmer.
Eventually, the thermostat will stay at a partially opened position where the cooling by the radiator just matches the necessary heat loss through the radiator.
If there is not enough water, the surface area of the radiator is effectively less.
If the radiator is blocked, or the fan is not working properly, the surface area of the radiator is effectively less.
If the thermostat doesn't open properly, the radiator is not sufficiently utilized.
If too much heat is generated by the engine, it can over heat (heavy load at low speed will make a lot of heat without spinning the water pump fast enough, for instance).
These are a few preliminary tests to see what's going on. With a stone cold engine, start it and let it idle. The heater hose leaving the thermostat area should begin to heat up but not the upper radiator hose.
Once the heater hose starts to become uncomfortably hot, the upper radiator hose should start to warm up, slowly at first.
If the heater hose does not heat up, there might be insufficient flow throw that part of the system.
There is a quick check a shop can perform to see if you have exhaust in the water. There is a syringe they can use to draw the vapor in the radiator through a sensing liquid. If it changes color, you have a head gasket leak.
The radiator cap only need to be replaced if it is letting the coolant move into the reservoir improperly. If you coolant level remains fine, that is probably not a problem.
Jun 20, 2010 |
2001 Cadillac DeVille