Man that sucks. Sorry to hear about your mishap. But there are several factors that could lead to your engine locking up.
Bearing overlap: This occurs when one of the 2piece rod-to-crank shaft bearings gets worn so thin that one piece is force or wedged under the other piece. The unsmooth surface now creates heat, enough to actually allow the pieces to dig into each other and fuse together resulting in engine lock. Not to much damage caused by this. Get the crank resurfaced, new rods and bearings+ main crank bearings.
Piston lock: This occurs when there is enough heat generated by the friction between the piston rings and the cylinder wall that the piston becomes seized within the cylinder. This is usually due to low oil level, old oil which has lost all lubricating ability, an overheat condition due to coolant system.
You may be lucky enough that it cools down and is free again, but will still require a rebuild due to the stress levels that have been exerted at the point of lock-up.
Blown head gasket: This is of course the gasket that creates the seal between head and block. Both oil and water flow between the head and block. When the head gasket breaks down coolant can be forced into the oiling system leaving you with a non-lubricating milky combination of coolant and oil. This will skyrocket engine temps with there being a large decrease in coolant level and improper lubrication from the oiling system. Yet a blown head gasket can also be almost harmless and just leak externally. There are many different ways the gasket can fail, all with different outcomes and repairs.
Accessory lock: this is a good one and commonly overlooked. Simply as stated, one of the accessories belt driven by the crankshaft has locked up stopping the engine. It takes a strong belt to stop an engine but I've seen it several times, especially when at idle or in a low load level. Quick fix, cut belts off and attempt restart. If restart is not successful, attempt to turn crankshaft bolt clockwise with large breaker bar.
Timing belt jump: This is BAD! The 3.4 is dual overhead cam, meaning there are 4 camshafts controlling valve operation. They are driven by the crankshaft via the timing belt. This guy jumps a tooth or breaks and your whole day is ruined. I'm not sure if the 3.4 is an interference engine or not, but in worst case if it IS, those valves left in the down position during moment of tooth jump or belt failure are immediately crushed or bent by the piston. Pistons probably suffered damage as well.
The crunching noise, that's not as bad as long as there was no bang or loud pop (rod punching through block) Did you have a big puddle of oil under the car when it stopped? As long as you were not smashing on the throttle there's no reason to believe that anything is broken. It takes a lot of force to break a rod, you'd just about have to be at wide open throttle or towing.
It's hard to diagnose without having it in front of me, but at least now you have basic knowledge so hopefully you won't be swindled by the repair shop. They will more than likely say that it requires a complete rebuild or a new motor. This may not be a bad idea with 118K mile on it. The fastest and most cost effective way to fix your problem due to total engine failure would be to replace it with a low mileage (<40K) Japanese imported engine. Search the internet, there are lots of companies that sell these. The Japanese have their engines pulled and replaced with NEW ones at 40k by law. That's just broken in if you ask me, but oh well, send em over here.
Good luck, hope this helped. :happens:
