99 s70 2.4 base , overheat / boil over at overflow

[nonturbo]

Hey guys, Overheat /overflow boil over at idle, thermostat changed, water pump new 7/16, never heat problem before with the exception the fan would come on after key off, ran for 5-6 min. Now fan issue may be point of interest, will operate with a/c on, but intermittent with a/c off. Thoughts are ECT sensor malfunction... any ideas Thanks.

[wizechatmgr]

Pressure cap

[abscate]

Pressure cap, split hose, split reservoir preventing system from pressurising.

[nonturbo]

Thanks abscate, From cold start, with cap removed, has normal temp increase and flow , then it began to boil out at a higher temp than I'm used to seeing, looked like a geyser, like almost at scald temp, about a gal of fluid, so then I shut down ...
When this issue showed up there was weak spot on lower hose at clamp that burst, thought that low fluid level was culprit for overheat, steam from reservoir, did quick repair to get home... thought that was issue, repaired tested again and reservoir hose at clamp did the same, so the pressure/temp in system has never been like this before.
New ECT on the way, and hoses. Hoping

[erikv11]

ECT wouldn't explain this behavior, unless maybe if the fan was *not* coming on enough. But you're not seeing that.

As much as you may cringe to consider it, at this point I might be doing a check for exhaust gases in the coolant. Sounds as if pressure is building higher than normal, and blowing out the web spots in your hoses. That can happen with a head gasket breach. The car has enough symptoms to warrant a test, and in this case if the test was negative then I would rule it out as a suspect. Good news is head gasket failures without overheating are rare on these cars, but I would check it.

[RigsPGT]

Change that cap, it might be culprit. Plastic inside it might be in pieces and the system is not holding pressure.