I just replaced the lower radiator hose (the one underneath the air intake hose on the driver side) yesterday, some coolant were lost during the process, trying to refill it but I can't seem get it topped off. steps I took:

After I installed the new hose, squeezed the new hose a bunch of times to force some air out
Filled coolant in radiator up to its neck
Started engine, put a diy no-spill-funnel in the radiator neck, waited for engine to get hot. Saw bubble burping out and coolant rose up then went back down, topped it off.
Fan came on, coolant got hot and rose up into funnel, started to see a little bit of steam. shut off engine.
Coolant in funnel went down completely after a few minutes, disappeared from radiator neck
Topped it off (maybe a couple oz), then it went down from neck again. no leaks on the ground.
Repeated this a few times, same thing. wont stay topped off.

Is this normal? any idea?

vehicle is a 09 mazda 5.

 

Is there any coolant in the reservoir on the (vehicle’s) right side of the motor? It has max/min as well, and you should be able to fill through that in normal times. If it’s dry the line is likely dry as well, so that’s a not insubstantial amount of coolant it’s missing. In normal usage it should bleed air up into that reservoir and pull coolant down.

 

Yes, reserve tank was filled to the min line.

 

I’m happy to have someone smarter correct me here, but if I’m understanding you correctly you’re running the motor with the cap off so that the heated coolant expands, and for air to work it’s way up the top of the radiator neck and get out of the system. If you’re shutting off the engine and letting the coolant drop back down with the cap still off it’s just going to pull air back in as it cools. Right? I’d think you should get it good and warm up as high as you can, cap it, and shut it off. Then as the coolant cools and drops I’d hope it would pull fluid in from the reservoir instead of from the wide open neck of the radiator. If you get it to start drawing from the reservoir, then you should be able to just add new fluid there instead of having to uncap the system. Air should continue to work it’s way up and be replaced by that fluid. Just make sure to add fluid to the reservoir so it doesn’t go completely dry.

 

yeah, i think that's what I did wrong. I left the cap off and let coolant dropped off. should have put the cap back on when it reached operating temp.