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[dallasdoer]

What defective seals/gaskets [besides the obvious head gasket(s)] could cause steam [super-heated water entering via normal channels (i.e., via the coolant reservoir) when the engine is not operating] to infiltrate the heads and/or settle in the crankcase?
                                                  Objective

To avoid now needless repair time and costs or to cause other unnecessary repairs.

Givens (set of facts):

2000 Cadillac Catera engine is dual overhead cams. It has a cast iron block with heads of aluminum/alloy and was been relatively problem-free since bought with 7,000 miles [lil’ old lady lease-return]. It just turned 90,000 miles. Dealer says they replaced the timing belt and tensioner around 20k; also repairing an oil cooler leak under the intake plenum [car developed a minor leak worsening and later found to be heater control].

Driving at highway speed on a very hot Dallas day [over 100 degrees] engine stopped without notice or any notice by the driver. (It appears that the radiator sprung a leak and emptied coolant sufficient to overheat the engine).

When the engine shut-down the driver attempted to restart it, while coasting in neutral on the highway. The starter motor turned but the engine would not restart. 

After coasting to a stop, the engine compartment was smoking. The driver [hoping to cool it to avoid melting rubber seals] added regular tap water to the reservoir, which produced a significant amount of steam and whistling noise when entering the engine.

After the engine cooled, driver tried to start the car - finding the starter motor turned very fast, apparently not engaging the flywheel [or suggesting a broken timing belt.]

Driver had the car towed home. The next day he added water to the reservoir which infiltrated the crankcase [suggesting busted gaskets somewhere]. He then left the car in that same state, in his garage [for few months while driving another car].

Upon recent disassembly and inspection of the timing belt, it is found in good condition i.e., it is not broken or frayed [the teeth are NOT spun down or missing at the crank balance pulley gear/sprocket]. Also, prior to releasing belt tension, it was near impossible to manually/hand-turn the crank (after draining the crankcase). However,
On removal of the intake manifold, rust on the underside of the intake valves on both sides of the engine is apparent. Obviously, water or steam entered those areas.

From these facts, it appears the car reached a sufficient temperature to cause the ECM to shut down operation [however, the starter motor turned (as if unimpeded by resistance suggesting the solenoid was not engaging the flywheel [by failsafe engineering].

[Gaffers]

I would fear that the HGs may be blown.  It can be confirmed by a cyl pressure test but what you describe and the fast turnover on trying to start suggests a lack of pressure in the cyls.  Normally the V6 heads are pretty robust but I learnt this summer from an expert that when any engine overheats after droping the coolant the worst thing you can do is add water/coolant as this cools the engine in a ununiformed manner which will most likely warp the heads.  The best thing to do is allow it to cool down naturally by opening the bonnet and leaving it.

Sorry, this is prob not the news you want to hear but DIY you can do the job over 4 days quite easily, less if you are an experienced mechanic in which case a weekend.  You will need to get the heads skimmed though and it's a good time to refurbish them at the same time

[2woody]

it sounds very much like the head gasket or gaskets have blown.

There is no ECU strategy to stop the engine if it gets too hot - it will have stopped because the excess coolant in the combustion chambers was preventing the spark doing its job.

the starter issue is one of the cranking speed being too high because there is no compression - due again to there being compromised head gasket(s)

On the plus-side, Catera head gaskets are relatively easy to change

I can offer to come and do the job for you - my rates are reasonable 

[feeutfo]

Hg fubar, unless there is a leak from throttle body (uk car, not sure on catera?) which is very unlikely.

Sorry.