LS Engine building pressure

[paperchase905]

Thanks for taking the time to read my thread because I need some help -
I have a 2000 Lincoln LS V8 that I bought a couple months ago for under $1000.
Was running rough @ idle & when it was moving when I got it, since then i have replaced -
Water pump
thermostat
serpentine belt
8 coil packs & plugs
oil & fuel filters
new coolant bottle
heater core got flushed
It's still running a little rough @ idle but not when moving.
Ran hot last week (because of cracked coolant bottle) & I took it home after it cooled down plus I added a half bottle of coolant.
Now after all that the engine is building up pressure to the point it blew off a coolant hose twice (the shop had it when this happened & they replaced the hose clamps). Picked it up today from the shop & they told me to drive it home with the coolant bottle cap loosened to release pressure. Drove home about 15-20 mins from shop on freeway & the coolant bottle was smoking.
The shop is saying I need to swap motors now.
Said they did compression test & it came back ok but they can't figure out what causing the pressure build up so I should get a new engine.
Lincoln Dealership told me today to bring it in & they would diagnose problem and fix it.
But before I made my next move I wanted to create this thread for some advice.

What could be causing this engine build up?

Any answers, suggestions, advice, fixes would be greatly appreciated.

 

[R34SklnNsn]

Sounds to me like a head gasket or crack that may leak cylinder pressure into the coolant system when engine heats up.

 

[joegr]

Head gasket problems with the 3.9 are so very rare that you need not consider it.
The hoses may be popping off because the plastic parts are degraded. Basically, you need to replace every plastic cooling system part. This includes the hoses. We have all been though this. Also, it is very very important that you refill and bleed the system exactly as instructed here: http://www.lincolnvscadillac.com/tech/drain-lincoln-ls-cooling-system/

The cap on the degas bottle releases any pressure over 15 PSI. If hoses are coming off, it's not because of excess pressure. It's because of the wrong clamps used or the ribs in the plastic that the hoses go over are gone.

 

[1LoudLS]

The cap on the degas bottle releases any pressure over 15 PSI. If hoses are coming off, it's not because of excess pressure. It's because of the wrong clamps used or the ribs in the plastic that the hoses go over are gone.

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