My OEM rad filler cap rubbers seal was looking rotten so I went to a local shop to pick one up and I noticed that the new cap has a relief spring on it like the ast Cap. I been driving on it for two days and everything is ok but I was wondering if I should go back with one without the relief spring? Will this harm anything? The cap also shows 16Lbs. The guy from the local shop said that was the correct one.

 

I can tell you right now the guy at the shop you went to is wrong. Go here and you'll know.

https://www.rx7club.com/showthread.p...t=fd3s+cooling

 

Two cap, one has no pressure seat (just a plainc cap) this one goes on the fill neck on the thermostat housing. The second one is the pressure cap and goes on the AST. Running two pressures caps is incorrect.