Misfire and Coolant Loss Dodge 4.7 – Possible Head GasketDecember 6, 2009 11:40 am Auto Specialty Tools, Chry. 4.7 Problems, DIY, Head Gasket Repl., How To Auto Repair, Jeep, Tech/Mechanic
It’s best to eliminate the simple possibilities first when diagnosing problems with any vehicle. Coolant loss? Pressure test the cooling system and see if there’s any external leaks. But what if there are no external leaks? Then there’s a possibility that the coolant may be leaking inside the engine. Due to the combustion chamber pressure being higher than the cooling system pressure, coolant can leak into the cylinder when the engine is turned off. When the motor is running the coolant that leaked into the cylinder, will be burned in the combustion chamber and in the catalytic converter, leaving little indication of a problem since tailpipe emissions may seem normal. The 2002 Dodge Durango featured in the images had not only coolant loss, but also had a history and a stored misfire code for the number three cylinder – P0303. Someone previously had replaced the #3 spark plug in hopes of curing the problem with the misfire… needless to say it wasn’t going to be that easy. With the spark plug out and pressure testing the cooling system the #3 cylinder filled with coolant quickly. So much for a simple repair.
After further inspection, a pitted area between the coolant passage and the combustion chamber was found. Pitting like this can be caused by electrolysis – an electric charge in the cooling system. A reading may actually be taken with a meter in the coolant. Over time the electrolysis can eat away at the aluminum until the gasket can no longer seal. A cylinder head like this can be machined as long as the pits are not too deep. If the damage is too deep replacing the cyl. head is the only option.
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