[subiesailor]

The very short compact heads and the way the subaru blocks are built its pretty rare to see cracked anything given how compact and strong they are. As mentioned above you would need to cook the **** out of the engine and just beat it to death to end up with cracked heads or a block etc.

Sounds to me like the classic crappy HG job. The HG job is only as good as the skilled hands that do them which case you should never see another HG failure if its done right and your not keeping the car to 250-300,000 miles etc

 

[subiesailor]

A non OEM thermostat could cause this type of temp issues and could eventually cause HG failure or worse due to it not managing the coolant and engine temp correctly. This is pretty common experience for people who have cheap aftermarket thermostats put in their car by mechanics or them selves vs the subaru brand OEM tstat

The cycling of the temp makes me think the Cooling system and engine were healthy except for possibly the Tstat was not correct ie non OEM and so when it restricted flow car warmed up and when it finally allowed flow the otherwise healthy cooling system started to do its job in cooling the engine down.

Tstat would be the #1 suspect I would pull it and see if its OEM if it is not I would be calling the HG shop and reviewing the parts list they replaced and be pushing for some money back on the job they F-ed up.

 

[subiesailor]

Just had the after market thermostat changed today with a OEM one, so far so good.

Non oem tstats are famous for causing this sadly in many cases the issue doesn't get solved till the cars owner has nearly melted down the engine multiple times and pretty much destroyed the HGs even if they were good to start with.

Should have been the first thing to be checked and fixed right away. Fingers crossed you don't have any heat related issues caused by the hot running temps prior to the tstat replacement

Just a tip don't take any more cars to the shop that used the non OEM tstat on the subaru! Given every subaru mechanic worth half their salt knows that subarus are funky and weird about Tstats and to stick with OEM.