coolant overflow tank going down

[Pmlecom1]

I have recently rebuild my motor, AGAIN.  79 Invader 440.  I have burned about one fuel tank so far.  Checking the sled over after every ride.  I've had to top off my coolant tank three times so far.  I know the coolant expands and would blow out the rubber hose just below the rad cap, But how much should that be?  I just did 25 miles and my tank has gone down 3/4" .  The tank is only 2" deep.  Am I over reacting or could their be something wrong?  I don't want another melt down.  Last time one head was warped and glycol sprayed the piston top, causing a minor melt down. A machinist lapped it back into shape. 

[mswyka]

We have one Invader with sleeved cylinders that would not seal correctly to the head gasket.  We would routinely lose coolent into the cylinder on this sled.  Finally replaced the head gaskets with 4/6 gaskets and have not had a problem since - the coolant level stays constant.  Our 340 Invader stays constant also.  Our 4/6 held a consistant level also.  If the level is going down, and you have given it time to chase out all the air bubbles out of the tunnel cooler, it is likely leaking.

Are you sure that you are not leaking someplace else?  Water pumps can also be a culprit.

[Pmlecom1]

I am going to ask my buddy for his rad pressure gauge tool.  Test it to see what might be going on.  Pump it up to 15 psi and watch to see if it maintains there.

[rminier]

 I would certainly do the pressure test for peace of mind. My Invader always loses about 3/4 inch out of the coolant tank after a ride that gets the coolant temp. warmed up.
  My newer sleds have a coolant overflow bottle, which I like, that captures the overflow and then returns it to the system. It's always nice to pop open the radiator cap and see the coolant right up to the bottom of the cap.  I think the Auto manufacturers started using the overflow tanks in the early 70's.
  I think it is absolutely normal to find the coolant tank has dropped 3/4 inch after a ride....as long as it doesn't continue to drop. As you mentioned, as the coolant warms up, it expands and runs out of the black hose down through the belly pan.
  You still have plenty of coolant in the radiator, the heat exchanger, and the motor.
  As I said....as long as it doesn't continue to drop below that 3/4 inch low level, you should be good.