Sorry for the rambling and hope this makes sense.

This question entered my thoughts while I was putting the ball valves in to turn the heat off for the summer. I was refilling the radiator through fill tank on the side of my engine compartment and it says to fill the tank to the half way point with the car cold. Easy enough but, how full does this get the radiator? I measured the top of the radiator from the garage floor and it is around 28.5 inches or so. I measured the mid point of the fill tank and it is about two inches shy of filling the radiator. I went ahead and added enough water to fill the radiator. This left about 3/4" in the fill tank for air space. I know the car is going to puke out what it does not need. Is having too much water a problem?

I would have thought that filling the fill tank to the halfway point should have filled the radiator to the top ensuring the best performance from the radiator. Why would GM not fill the radiator all the way? Filling the radiator all the way should keep some corrosion from forming in the top part of the radiator correct? Anyone understand anything I have said so far? It makes sense to me, I was just curious about the whole thing.

Any thoughts appreciated.

 

I don't have an answer to the radiator fill dilemma..

But considering the point about keeping the top of the radiator from forming corrosion, isn't there a problem with this happening to the heater core while it is blocked off to prevent the heat in the cabin?

It was about 80-something today and I was cooking in my C3, so I was thinking about blocking off the heater core. Though I would rather cook on the few really hot days than have to replace the core because it was left in a semi-wet state that allowed it to rot.

So same thought about the corrosion here, just a different piece.

 

I am not sure what you mean.
The puke tank will rise when car is hot and shrink when cold.
Usually the radiator is filled and cap off start car and wait for thermostat to open and this lowers rad. fill too top and cap.
puke tank then filled to cold mark.
when car gets hot and pressure increases the extra rad water goes to puke tank.
when car cools rad sucks water back in from puke tank.

 

I don't have a fill tank on my 74, I have an overflow tank. When the antifreeze gets hot the radiator cap releases the pressure and the overflow tank fills up a little. When you shut the car off the radiator cap becomes a vacuum valve and sucks the antifreeze back into the radiator, doesn't the fill tank work the same way?
As far as the Heater core, originally I had a vacuum controlled shut off valve only on the intake (5/8) side when it failed I installed two ball valves (one one each heater hose) do you think that the ball valves should be opened every month for a few minutes to let fresh antifreeze in? PG.

 

The radiator in my 70 does not have a fill cap on the radiator itself. There is a tank mounted on the inner fender on the passengers side that has the pressure cap. This is where the filling is to be done. There is no overflow/recovery tank. If the car has too much coolant, it just goes to the ground. Later vettes had coolant recovery tanks.

I do like your idea about keeping some water flowing through the heater core once in a while. Good thinking. It cannot hurt any and is easy enough to do.

 

On the system you have the radiator remains completely full all the time. The smaller hose at the top right of your radiator circulates coolant all the time and is there to also purge any air that is in the system to the remote expansion tank. The pressure cap on the remote expansion tank will puke out any extra coolant that is not needed.
A very good system.
This system is still used by most European mid engined exotics.