maybe? the rear heater lines are at the firewall and fairly high up. so as the system leaks down, it could drop below the level of the leaky hoses and lessen the coolant loss. when my radiator had a hairline crack in the top tank cap a similar thing happened...it wouldn't leak until i topped everything up. then i had a puddle as large as yours. over days the overflow level would drop as the system self purged onto the ground...eventually stopping once it got low enough. if i took off the cap, coolant was not all the way up.hey man. thanks for the eyeballs and also the thoughtful response.
is it possible that i have a leak in the rear heater lines but that when the "system" (whatever that means) does not have the full amount of fluid in it - well it doesn't leak? but when it has a full amount of fluid in it it does?
maybe that makes no sense and you are saying there would have to be a different reason for there to be that much fluid on the ground.
i admit it is kind of weird. the overflow jug will hold coolant. but it does not stay there. the radiator system will take additional fluid when "burping it". and the valve to the overflow jig appears to work both ways.
is it possible the engine cooled after i burped it? it was full of coolant? then it ducked in the amount remaining in the overflow? then it puked it out overnight? but the leak is small enough to not lose all of it?
the flow diagram (thanks @NLXTACY) shows everything on one page. however the direction of the arrows for the PHH and heater valve are backwards; if you want to check yourself, the arrow on the valve clearly points from right to left. and therefore the main heater core arrows both flow towards the motor so that's not right. but its a great picture nonetheless!
remember that liquid expands when it heats up. so coolant is pumped into the overflow reservoir when you are driving, and is pulled back in as the engine cools off overnight via a siphon effect. the overflow is not under pressure. and the level in the radiator shouldn't change.
when i've filled up my system, i find that if i slowly add coolant it self burps. once i get the radiator completely filled, the extra will drain into the overflow if i pour VERY slowly. when i've done this it has been in my slightly sloped driveway so the nose is high.