As the title suggests, I can't seem to get my screw in freeze plugs to completely seal. The block is an Aluminum Pond Block with steel pipe thread plugs. No O-ring, just sealed with Permatex Aviation Sealant. I usually test my systems with compressed air (at 15psi) and spray all fittings, hoses, plugs, etc with soapy water to make sure I'm sealed up. This particular engine however is giving me fits. I was able to fix one screw in plugs by cranking the plug a bit tighter but I have two more that have a very small leak. It will not blow bubbles from around the screw plug, it only foams slowly which means it's a small, slow leak. After reading some other forums and comments, guys have stated that the leak will subside once the engine heats up and 100% Ethylene glycol will not leak as readily as the air. I'm not certain about these ideas. And, the system will leak all the way down to 0 psi air in the system if left overnight. Any ideas ? It's already in the car, so do I just fill it 100% with antifreeze and hope for the best ? I don't want to crank on these plugs any further as cracking the casting would be a tragedy.