Replaced water pump, hoses, t-stat, fan clutch, rad cap and bled system as per the forum. Plenty of air still in the system. CEL says cyl 7 and 8 missfire. Runs normal for about 15 minutes and then gets hot. Suspect head gasket(s). Anyone tried Red Devil? Any thoughts?
Schwab

 

Are you leaking coolant externally or internally? Does your exhaust smell like coolant? Misfires in 7 and 8 could be a HG leak. If you do have a bad head gasket there is no magic juice that you can simply pour in. Not sure what you mean by plenty of air in the system, you said you bled the system correct? That should get about 95% of the air out and then a top off or 2 is all you should need. Anyhow a bad head gasket is not going to cause overheating unless you leak all your coolant out. Air in the lines or a bad radiator can.