Hi all. Hope someone can help me. I have a '94 XLT with 225k miles. Engine has been knocking terribly and I haven't been able to get it to stop. I have done the following: Replaced plugs, wires, coil pack. Run Seafoam through the intake twice, let it sit, and then ran the engine about 15 miles at 3k rpm. Check engine light went on when I did this last, but then went off. I ran the engine pretty hard. Then changed the oil. I'm running 91 octane premium because anything less knocks worse. I have been running Arco gas recently. It's the least expensive around generally, and am wondering if that may be part of the problem? Also wondering if a blown head gasket could cause knock. I am loosing some coolant, but I think it could be a slow leak from around the neck of the thermostat cover, as there is some buildup around the hose there. I can also smell coolant under the hood. How can I diagnose or rule out a bad head gasket? Any help would be appreciated! Thanks!