| Subject: Re: overheating symptoms |
Author:
Glen
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Date Posted: 06:47:17 09/05/03 Fri
Author Host/IP: 67-39-236-58.ded.ameritech.net/67.39.236.58
In reply to:
Burnplant
's message, "overheating symptoms" on 14:06:14 09/04/03 Thu
I'm not totally clear what the engine problem is. You're saying the engine is overheating, but that the engine and oil temperature levels seem okay?
Going back to basics, the engine produces heat and transfers it to the coolant which is circulating through the engine only when the engine is cold. As it heats up, the thermostat opens up partially, and a small amount of coolant circulates through the radiator, and the rest just circulates through the engine. As the engine heats up more, the themostat opens up more, allowing more coolant to flow through the radiator. This continues until the amount of heat rejected to the air is equivalent to the amount of heat generated by the engine due to its current load/speed.
So, a properly operating engine always has a thermostat that is partially open and regulating the flow split between radiator and radiator bypass coolant flow.
If the engine produces more heat than the radiator can reject to the ambient air without forced air flow through the radiator (say at idle at a stop light for a long time), then the thermostat opens all the way up and allows all the flow it can to go to the radiator, and at some point this still is not enough cooling. The sensor tells the fans to kick on, and the extra heat rejection due to the forced air flow in a sense increase the "size" of the radiator, and the engine cools off.
Now, to overheat you have several possible reasons.
Restricted or low coolant flow: This could be caused by either plugged radiator or engine coolant passages, or by a water pump that is not spinning. The latter would (should) cause a very fast overheat. I've not run across a water pump that has had any impeller damage that would cause a quick overheat, but Marquinn has so do check the flow.
Low coolant: Not enough coolant mass to transfer the heat to, and low coolant level in the radiator means the effectiveness drops.
Bad thermostat: If the t-stat does open properly, then too much hot coolant bypasses the radiator and heads right back into the hot engine. This is the most likely cause, but you said you replaced it, correct?
Fans not coming on: This would cause an overheat at idle, but not when the car is moving. Sounds like you forced the fans on and still overheat.
Plugged radiator externally: If the outside of the radiator is plugged with debris, then the heat can't be rejected to the ambient air.
As Marquinn pointed out, I'd suspect a plugged radiator or clogged internal engine passages. Water pumps generally don't stop pumping, they usually have go bad because of seal leaks damaging the bearings. Also, without any coolant flow you should overheat very fast. Try a system flush, and/or see if a local shop can clean your radiator if you take it to them...let us know what you find out...glen
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