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Originally Posted by Sharky
Is there anything else that I could do diagnose it?
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Lots of things:
The thermostat could be frozen partialy closed. With a thermometer, verify the temperature on a metal part of the radiator housing. This will also give you an indication of the effectiveness of the fan control switch as you can observe the temperture rise to the operating point(s) for the fan(s). Check a service manual. Usual range is 110-125° C. The top of the radiator will be the warmest, the bottom will be the coolest. The sensor is usually placed near the bottom of the radiator. When (if) the thermostat opens, the temperature should decrease by at least 10° C within a few minutes. If not, spray cold water from a hose on the front of the radiator (careful not to flood anything in the engine compartment).
The timing could be retarded or the spark plugs could be deteriorated so as to provide late/difficult ignition.
Fuel mixture could be too lean under load. You didn't state if your car was injected or carburetted.
The radiator could have minimal fluid flow - clogged tubes. Turn the heater on to it's warmest setting w/high fan speed and see if it stabilizes the temperature.
The water pump could be worn out (impeller not efffective or cavitating)
A blown headgasket has to `blow' something somewhere. One place would be coolant into the oil supply. This is indicated by `milky' or `grey' colored oil on the dipstick as well as the filler cap as you have noted.
The other possibility would be combustion gasses escaping into the coolant. This can be identified by very carefully using a rag or some other method, remove the radiator cap (not the cap on the catch bottle) while the engine is idling. Slowly increase the revs and look for bubbles in the coolant. If you have them, it is either water pump or head gasket. Opening the catch bottle will never produce any sound as the system is not sealed at that point. The sealing is done at the radiator cap which incorporates a pressure relief system to vent into the bottle and siphon back when cooled.
