
Originally Posted by
joseph_abri
how do i check the source of my car's overheat problem, its a chevy optra... here: the temperature rises up to almost 3/4 or even higher of the temp gauge... even with a bit short distances. it is gulping water every trip. it just happened a couple of days ago, both fans (auxiliary and radiator) working, replaced the auxiliary fan lately, and the thermostat... there is extreme steam pressure in the upper radiator, its hotter than the other hose, based from my touch, (this is where the thermostat is located), a day ago, there was steam coming out of the radiator reserve cap, replaced the cap now its ok, when i replaced the aux fan yesterday i removed and returned the upper rad hose connecting to the radiator, and clamped it, perhaps the clamp is not sealed enough as of today i can feel the steam pressure escaping from the hose that is connected to the radiator, might come back to the mechanic who put them yesteday to tighten the clamp... but i am not sure if that solves it, because there is still the overheat problem to think of,. how do i solve it...
the rad months ago was replaced along with the aux fan and thermostat not more than 3 months ago, with chevy service center, if it continues heating the engine it might destroy the engine so i wanna pinpoint the problem.. and diagnose it correctly, i dont like the idea of replacing everything, just to make it work... if one can diagnose where is the source, well be answering the problem right on..
Well, if your car has been running fine prior to this problem, then there is a high probability that the trouble is within the cooling system only.
[SIZE=4][SIZE=4]General Description [/SIZE][/SIZE]The cooling system maintains the engine temperature at an efficient level during all engine operating conditions. When the engine is cold, the cooling system cools the engine slowly or not at all. This slow cooling of the engine allows the engine to warm up quickly.
The cooling system includes a radiator and recovery subsystem, cooling fans, a thermostat and housing, a coolant pump, and a coolant pump drive belt. The timing belt drives the coolant pump.
All components must function properly in order for the cooling system to operate. The coolant pump draws the coolant from the radiator. The coolant then circulates through water jackets in the engine block, the intake manifold, and the cylinder head. When the coolant reaches the operating temperature of the thermostat, the thermostat opens. The coolant then goes back to the radiator where it cools.
This system directs some coolant through the hoses to the heater core. This provides for heating and defrosting. The surge tank is connected to the radiator to recover the coolant displaced by expansion from the high temperatures. The surge tank maintains the correct coolant level.
The cooling system for this vehicle has no radiator cap or filler neck. The coolant is added to the cooling system through the surge tank.
Steam means boiling water, low pressure, and air in the system. The cooling system of the Optra is a pressurized system. For the Optra, you will see two hoses that go the the surge tank, one for the expansion of the coolant and the other for the return of the coolant. These are controlled by valves.
Surge Tank
Open Pressure of The Pressure Valve
kPa(psi)
117.7~147.1(17.07~21.34)
Open Pressure of The Vacuum Valve
kPa(psi)
9.8(1.42)
If there is failure here, the cooling system will not function correctly.
If the pressure valve opens too early (at a lower pressure) the coolant will boil over. Hence the steam.