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06 Commander 4.7 V8, 117K miles No issues whatsoever until today. Wife came home this am after a jaunt around town and said it was running hot. I looked and gauge was pegged. Coolant reservoir is empty. We have not seen one drop of coolant on the ground and there are no signs of any leaks. Cap seems fine as well. Slowly opened the cap and let pressure out, pressure went into the reservoir and some coolant went int here as well.

Water Pump??
 

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Check the oil for signs of coolant, high level, white gunk, foamy. If it looks okay. Fill it rad with water again and check to see where its leaking from.
I agree, just make sure you allow it time to cool off or fill it with the engine running.
 

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Had same issue with my 06 4.7, was told it was water pump/thermostat, replaced both, ended up being blown head gasket. these things seem to be really finniky (sp) about overheating.
 

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I was going to say, the 4.7L and 3.7L (same motor with 2 less pistons), I've read stories about the damage they can suffer from overheating that most engines seem to survive without a problem. I guess the engineers made some decisions with the aluminum heads that don't make them as durable as other motors, and which they reversed over the years in response to the problems, so later models of these engine probably aren't as prone to the head/valve problems that the earlier ones did when they overheated.

Square Grouper, it sounds like your problem is a leak in the cooling system, a small leak allows a small amount of coolant to be lost over time and not noticed by the owner, when it eventually gets low enough, you'll start to suffer overheating.

It could be a bad water pump and the coolant lose was the result of boil over. But boil over would mean you kept driving while the motor was getting hotter and hotter and you should have seen steam coming from under the hood. Water pumps rarely fail without leaking, looks closely at the water pump and see if you can see signs of a leak around the shaft going into it, or the weep hole that is usually just below the shaft. If you've been running just water or way overdue for a coolant change, its always possible the water pump impeller is eroded/corroded away and that is causing the problem, if so your coolant would look horribley discolored with the rust from inside the engine.

It could be a bad headgasket or warped head, but you'd get signs of fluid mixing or at least some signs of contamination in the different fluids, oil and coolant.
 
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