Replacement Radiator O rings
 

I'm in the process of a cooling system refresh utilizing an ECS Tuning kit. This is the fourth time that I've done a 3 type or E53 cooling refresh but the first to include a radiator replacement. The ECS kit included 3 O rings in the radiator box. Diameter of 2 matches the upper and lower hose flanges and the third is smaller matching the expansion tank front hose flange. As far as I can remember never used any O rings connecting any hoses in the past, the rings are in the hose. No trace of any rings on the old parts apart from the ones imbeded in the hoses. Anyone know why these rings were included? Thanks

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Maybe they are thinking you might want to replace the o-ring in the hose collar if you don't replace the hoses? That's probably what I'd do if the new ones are the correct diams.

I think that's correct. My uncertainty was because the radiator was part of the ECS rebuild kit which includes new hoses. Also from searching BMW and O rings there are some post mentioning replacing the rings imbedded in the hoses can be difficult. Anyway just finished the rebuild so far no obvious leak after a short test.