Chevrolet: Over heating, water pump impeller, double wall pipe

Question
No my fan is coming on just fine. That's not it. Thanks anyways. Just trying to get another idea sence I KNOW it's NOT the fan, water pump ro radiator.
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Followup To

Question -
I know that it said 1993 but I'd thought I'd ask anyways. I have a 1991 Chevy Camaro RS. We've been having alot of problems with it over heating. We've changed the therm. 2 times and it's without one again now; water pump, and a new radiator. We have also put a new fan motor on it. I have a almost 3 year old son and the thought of riding around next summer with the heater blasting is not something I'm looking forward to again.
The cap is good. Can't find any leaking hoses. It's got good air flow. And the heat and air blow just fine.
I was wondering if maybe a freeze plug? Let me know what you think.
Thanks,
Hopless Mom

Answer -
Can you verify that the fan is in fact coming on at the right time?

Unplug the coolant temp sensor and the fan should be on all the time. If your car is still overheating, we'll know its not the fan or sensor.

You didn't say what size motor you had so I'm going to assume its the 305. The sensor should be at the front of the motor on the gooseneck where the thermostat is.

Answer
Possible causes of overheating:

A low coolant level, loss of coolant (through internal or external leaks), poor heat conductivity inside the engine because of accumulated deposits in the water jackets, a defective thermostat that doesn't open, poor airflow through the radiator, a slipping fan clutch, an inoperative electric cooling fan, a collapsed lower radiator hose, an eroded or loose water pump impeller, or even a defective radiator cap.

Some other causes:

* Excessive exhaust backpressure. A clogged catalytic converter is usually the culprit here, but don't overlook the possibility of a crushed pipe or a collapsed double wall pipe. Check intake vacuum at idle. If it reads low and continues to drop, inspect the exhaust system.


* Retarded or overadvanced ignition timing (may also contribute to detonation & preignition).

* Air pocket trapped in the heads.

* Scale build up in the coolant passages (needs a good rad flush).