Not sure we are on the same page. ??
Coolant expands when heated, and then contracts when again cooled. So a full radiator, with the coolant cold, absolutely will cause the coolant to expand when it is heated (the engine is running) and the pressure caused by this will force the radiator cap open (to the first stage on modern vehicles) and purge the [now] excess fluid. On all modern vehicles, there is an overflow bottle to catch this 'overflow' and hold it until the coolant in the engine and radiator again cool down (sometime after the bike is shut off). When the coolant cools and shrinks, it creates a vacuum and the radiator cap will again allow a 'leak' to the first stage, which is connected to the bottom of the overflow bottle, thereby drawing the original purged fluid back into the radiator.
I was merely responding to your statement "it really can't suck air into the radiator from an empty reservoir bottle." which is incorrect. If the coolant shrinks, creates a vacuum but there is no fluid in the overflow bottle (for whatever reason) then the cooling system cannot help but suck air into the top of the radiator. That is all I was responding to, the statement quoted above that you made in a previous post. If there were quantifiers in your post, I either did not see them or did / do not understand them. ??
Brian
i don't know how to explain it simpler than I did...
FULL radiator... NO Leaks, EMPTY bottle....
coolant expands, flows to bottle..(radiator still full of liquid...expanded, but still full)
Bottle is now containing the coolant that was pushed there... the bottle has a return line at it's BOTTOM... coolant is retained,sitting over the return lines hole in the bottle, sealing it from external air, temporarily, in this bottle...(radiator is still full....), everything begins to cool, and the coolant in bottle gets sucked back to radiator neck (via a junction in the thermo housing), once again
filling it completely full..with the now cooling rapidly, and contracting ( the opposite of expanding) juice.... if the radiator is FULL, it can't suck air in... just can't, as it is FULL.
Full make the radiator 'happy', and at that point, its done its job..
in truth, the catch bottle is a safety measure, only to prevent issues in the event of a "leakage, where fluid is dumped from the system,
externally..." like a 'massive coolant dump into the bottle, from extreme overheat, where so much coolant is spewed that it dumps out the overflow of the bottle itself...
If a failure occurs in a hose, or other flow path, where coolant is lost 'externally', even having juice in the bottle really won't help in every instance..., because the system would try to suck air from that failed part, instead of the bottle... depending on the location and severity of the failure..
we have seen this firsthand, with the 'chewing gum' seal on the C10 thermostat housing split line.. coolant bottle has juice in it, but radiator is a cup or more low... and
nobody can figure where the coolant went to...or why it didn't suck fluid from the bottle... because it puked out of that ring seal, and evaporated, and during the 'cooling vacuum stage' just sucked in air from the housing... till it all contracted, and re sealed... invisibly...
It was a dilemma that was pondered for 20 years on that bike, until Guy and I found it, and it was pondered profusely by both of us for quite a while, to close that issue.
from da book...
"The system is pressurized by the radiator cap to suppress boiling and the resultant air bubbles which can cause engine overheating. As the engine warms up, the coolant in the radiator and the water jacket expands. The excess coolant flows through the radiator cap and hose to the reserve tank to be stored there temporarily. Conversely, as the engine cools down, the coolant in the radiator and the water jacket contracts, and the stored coolant flows back to the radiator from the reserve tank.
The radiator cap has two valves. One is a pressure valve which holds the pressure in the system when the engine is running. When the pressure exceeds 93 ∼ 123 kPa (0.95 ∼ 1.25 kgf/cm², 13 ∼ 18 psi), the pressure valve opens and releases the pressure to the reserve tank. As soon as pressure escapes, the valve closes, and keeps the pressure at 93 ∼ 123 kPa (0.95 ∼ 1.25 kgf/cm², 13 ∼ 18 psi).
When the engine cools down, another small valve (vacuum valve) in the cap opens. As the coolant cools, the coolant contracts to form a vacuum in the system. The vacuum valve opens and allows the coolant from the reserve tank to enter the radiator."