quick question.. whats the upper filler neck for? i had this 2gen for a month now, and noticed that when i take the cap off, theres a gasket in there preventing fluid to be able to be added there. is it possible that the previous owner done that because it leaks? whats the PROPER way to add coolant to these vehicles assuming that the radiator and cooling system is empty? thanks fellas! Brian

 

on an s4 you add the coolant through the filler neck above the thermostat.

s5'd dont have a filler spot in that location so you use the neck on the radiator.

 

Damn, then I wonder why he had it blocked off then. Guess ill try to work that one out and make sure it doesnt leak on me. Thanks man, appreciate it.

 

It probably put it in there, because he was to cheap to buy the oem mazda radiator cap.

 

if im not mistaking the S4 filler necks with the caps use a gasket on the lower part but they use an o-ring on the top..so you should be able to just buy an o ring....

 

there is a paper gasket between the filler neck and waterpump housing. there is also an oring between the filler neck and the plastic piece that the cap screws onto.

s5's have a single oring between the filler neck and waterpump housing.

 

which radiator do you have? if you have an S5 radiator it iwll have a long neck radiator cap assembly.

You should try to correct that though because i could imagine air getting trapped in that upper neck since its the highest part of the cooling system.

 

with an s5 radiator do u need the overflow resevoir?

 

of course.

 

its an s4. but there arent any packings installed, so im assuming that is the reason that it has been blocked off just below the cap. no biggie though, i can get packings from work. ill let ya'll know how she turns out. thanks again for all the info!