Radiator hoses ballooning from pressure.
 

Hey Guys,

I have an odd issue with my S5. After running the car at operating temps for a little while, I noticed that the radiator hoses seem to get super pressurized causing them to balloon slightly. The amount of pressure in there is abnormally high when compared to other hoses. These are OEM Mazda Hoses and are just a little over a year old. The radiator cap is .9 bar. I have tried another .9 cap and the same result occurs. No coolant spews out anywhere or anything like that, but last week I did develope a small leaking crack in my waterneck. Now I am wondering if the pressure is what caused this or if it was just a coincidence. The pressure thing has been going on for quite some time now without issue, but I am concerned that this could lead to bigger problems like blown seals.

Motor is N/A and street ported. It has about 8k on it now since the rebuild. I am using an aluminum radiator that is supposedly an old Koyo unit, but it is unmarked.

Any input is greatly appreciated.

Thanks in advance.

water seal issue
needs a CO litmus test for combustion gasses in the coolant

else you can check yourself if engine is started fully cold but pressurises the hoses before its warmed much
( indicating the initial hose pressure is not a function of heat )

if both hoses hard before the temps get up much = water seal issue

if the top hose is hard and the bottom soft then it may be indicating a blocked radiator