'03 Disco SE
Join Date: Aug 2011
Location: Clearwater, FL, USA
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Cylinder misfire + overheating issues typically mean head gasket issues. Are you losing coolant? Is the cooling system bled properly?
Swap your ignition coils and plug wires from one side of the motor to the other, if the misfire jumps to the other bank then you know your problem is with the coil or the wires. If it stays on the same cylinder it's likely the gasket or a valvetrain issue.
Also, I HIGHLY recommend that you avoid throwing additives of any kind into the crank case. Seafoam is a good product to use in the induction system and gas tank (if you use it properly), but Restore has a spotty record. It's typically used in older, high mileage engines to extend useful life by a few thousand miles, but in newer vehicles like our trucks, all it does is clog the oil filter - this may be why you experienced the ticking. Modern engine oils have MORE than enough detergents in them to clean the engine. If the vehicle had regular oil changes using quality oil - the engine is clean.
What could have happened is that the Restore starved your head of oil, the lifter for cylinder 3 collapsed causing your misfire and tick. Switch over to a clean, quality oil (like Rotella T6) and a quality filter (Bosch or Mobil, Fram is JUNK) and see if the tick doesn't go away.