I usually don't drive my z for long drives, but today was a nice warm day.I drove from Los Angeles to San Fernando valley and back with no resting time in between. On the way back I caught traffic, in total about 1 1/2 hours of driving at about 90 degree weather.when I got home I parked the and turned off the car. Once I got off I heard a sizzeling sound and noticed coolent coming out of the front bumper.the coolent was coming out of the resivour, I waited till it cooled down and checked the water. The radiator was a little low from all the coolent that rushed into the resivour.how can I tell if it's the thermostat, head gasket, water pump and why did it overheat.

Doesn't sound to me like anything bad happened. Sounds like a normal cooling system doing what it's designed to do.

A gentleman recently wrote up a piece on cooling system function on the Bluebird (510) list. I'll see if I can find it. It really spelled out how things a supposed to work and what not to get paranoid about.....

Don't know if this will apply but used this method to tell if the thermostat was bad, stuck fully or partially closed.

Idle the car with radiator cap open.

Warm it up and watch the coolant level.

The level will begin to "bob" up and down (1" or more) and eventually overflow the opening.

Best practice is to remove and put it on the stove in a pot of heated water with thermometer and measure the temp when/if/how far it opens.

Edited September 5, 201014 yr by mlc240z

You know, one thing you can do is update your radiator cap with a new one. A weak radiator cap can and will bleed off pressure thus reducing the effective temperature of the coolant can take before boiling. Because of pressure and coolant the boiling temp in a good system will be raised to 240 degrees.

On a Datsun I had from a PO, somewhere along the way an 8# cap had been installed. Went to a 13# cap and shazam!! the whole system performed better.

Just changed the fluids,radiator cap and thermostat. I will run the car tomorrow and post up resolts . Stay tuned for update

Do you have an actual graduated gauge?

You know, one thing you can do is update your radiator cap with a new one. A weak radiator cap can and will bleed off pressure thus reducing the effective temperature of the coolant can take before boiling. Because of pressure and coolant the boiling temp in a good system will be raised to 240 degrees.

On a Datsun I had from a PO, somewhere along the way an 8# cap had been installed. Went to a 13# cap and shazam!! the whole system performed better.

I'll second this absolutely.

I just turned the car on and let the car warm up. The thermostat open but the water wasn't flowing like it should. By the way on my original post I forgot to mention that on the way home I heard a loud POP sound that now I pretty sure it's the water pump.any ideas.

Impellor may have fallen off. Just another one of thos 40 something year old widgets that should have been renewed before you started relying on the vehicle for reliable transportation, even if it is just for fun......

These cars are just loaded with 40 year old three quarters worn out widgets, any of which can and will leave you standing along side the road talking to AAA, if you can gae a signal.

Couldn't believe it but the water pump was in perfect condition. Still replace it, ran it for a while with no problems. Even though it seem to not overheat the water does not flow as it should. Would the radiator be bad?.

Did you refioll the water when the heater was open ?

Yeah ran it , and filled the water while running until it filled up.

I got to get the car good for Sunday for the Japanese classic car show at the queen Mary.whose going