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69 Big Block Expansion Tank Overflow (1/6)
 9/16/18 5:09pm
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

Hi All,
 
For the past year I have noticed that when I turn off my big block that there is a couple of drops of water under the drain hose from the expansion tank.
 
  • Water temp gauge reads at 155F, it's inaccurate, but never rises any higher. Even if it is inaccurate, if there was a temp spike I would expect the gauge to climb but it does not.

 

  • Infrared Thermometer on the thermostat housing reads 200-205F. From my reading this not unusual, and I take this reading a couple of mins after shutting off, so I would expect the coolant temp to rise with residual heat and not airflow.
 
  • Water pump was failing, observed through tell tale and replaced.
 
  • No water in the oil, no white smoke out of the exhaust, car was recently dyno'd and no smoke at all on full throttle.
 
  • When cold, the radiator is at the correct level, expansion tank is 1/2/ full. Expansion tank cap has evidence of coolant on the inner seal indicating that the level has risen in the tank.
 
  • Expansion tank cap is 15 PSI. This is new.
 
  • There is a very small amount of debris floating on top of the coolant, most likely from the failed water pump. The radiator was not flushed after the pump failed.

 

  • I am not having to top up any coolant
  • No external leaks on the radiator
 
**The radiator is a Harrison radiator, not the original, but quite old, and has a radiator cap. I have installed a blanking cap and the expansion tank is pressurised with the pressure cap. When I purchased the car there was a pressurised cap on the radiator and expansion tank.
 
The couple of drops that I see on the ground are clear not green but definitely coming from the expansion tank drain hose.
 
I am thinking of replacing the thermostat, I know this doesn't affect the engine temp, I would have no idea when this was last replaced. Is it worthwhile going to 160F thermostat to get the coolant to circulate a bit earlier?
 
Should I be concerned by the couple of drops of water?
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Re: 69 Big Block Expansion Tank Overflow (2/6)
 9/16/18 8:39pm
73shark
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Overland Park, KS - USA

Vette(s):
1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.


Joined: 7/9/2003
Posts: 550

I assume that the only way water can get in this overflow hose is when the pressure exceeds 15 psi. If that is the case, then the water level in expansion tank must be rising to the point that it has to go out that hose. You could try reducing the level in the expansion tank when it's cold to see if that corrects the problem. The coolant system temperature will increase thereby increasing the pressure when the engine is shut off and the coolant system is no longer being cooled by the radiator. This pressure increase may be why the water is getting into the overflow hose. Is the temperature gauge bad or is it the temperature sensor?

______________

1973 L-82 4 spd

Re: 69 Big Block Expansion Tank Overflow (3/6)
 9/16/18 9:06pm
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

73shark said: I assume that the only way water can get in this overflow hose is when the pressure exceeds 15 psi. If that is the case, then the water level in expansion tank must be rising to the point that it has to go out that hose. You could try reducing the level in the expansion tank when it's cold to see if that corrects the problem. The coolant system temperature will increase thereby increasing the pressure when the engine is shut off and the coolant system is no longer being cooled by the radiator. This pressure increase may be why the water is getting into the overflow hose. Is the temperature gauge bad or is it the temperature sensor?


Correct, the 15 PSI pressure must be exceeded.
The temp sensor doesn't appear to be correct for a 69, seems like its a 1957-67 corvette sensor, so someone has changed this out at some point, al the resistance values in the sensor are different hence the inaccuracy. I am assuming the plug on the end of the wire has been cut and changed to suit. I have no idea about the previous owner's logic on this decision...
 
I can purchase the correct sender unit but no idea where to get the plug for it, unless I buy the wiring harness.
The gauge reads zero when cold and heats up to 155F, so I think the gauge is fine. No symptoms of a faulty gauge or connections (I saw a Wilcox article about the different symptoms of a faulty gauge). I re-terminated the connection to the temp sensor, as the wiring was a bit frayed, but that did not make a difference.
 
I also noticed I have a new pack of radiator foam padding stick on's, which I am guessing is to block air moving around the radiator. Are there images of where specifically these stick onto?
 
I am not concerned about a couple of drops of water on the ground, unless it's a symptom of a much more serious problem.
 
If it was overheating I would expect a lot more coolant i.e. puddles on the ground not a few drops?

Re: 69 Big Block Expansion Tank Overflow (4/6)
 9/17/18 12:05am
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

I have also just had a thought......the tick mark between 100F and 210F is that 155F or actually 180F. I might not have understood the scale at which the gauge reads.

 
Gauge always just sits on the tick mark or just above.
Re: 69 Big Block Expansion Tank Overflow (5/6)
 9/17/18 7:44am
manchestersharkLifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.


Joined: 10/31/2007
Posts: 1981

What are the possibilities of condensation in the line, and not really antifreeze? If it's not green, and independent of another source of water, it may be steam in the tank from over flow, and condensing, thus dripping out.
Re: 69 Big Block Expansion Tank Overflow (6/6)
 9/17/18 5:39pm
NJAus
Former Member

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, - Australia

Vette(s):
Currently own a white 1969 427 Big Block Coupe C3 Corvette


Joined: 6/6/2018
Posts: 30

manchestershark said: What are the possibilities of condensation in the line, and not really antifreeze? If it's not green, and independent of another source of water, it may be steam in the tank from over flow, and condensing, thus dripping out.


Yes that could be a possibility,
There is definitely coolant on the underside of the pressure cap rubber seal