Citroen Xantia blown Head gasket?

[August]

Citroen xantia 1.8 16v 1999 manual


I've noticed my overflow cap hissing after stoping the engine and I didn't notice it before even tho i've been under the hood a lot. Firstly I tried buying a new cap - didn't fix it. Now I noticed top radiator hose getting hard when the car wasn't even close to operating temperature. Did a test of opening the cap after a day of sitting and releasing any left pressure, starting the engine, letting it run for a minute and opening the cap again. To no suprise I did hear a slight hiss.... Also when the car reaches around 60C if I try to open the cap - coolant splashes out

The car doesn't overheat...

So I'm suspecting a minor head gasket leak


What do you guys think?

[white exec]

If the HG is blown, you should be seeing bubbles in the expansion tank, and getting loss of coolant. Compression getting into the coolant will cause airlocks in the cooling system (which can interfere with the way the thermostat works, if the thermostat housing gets an airlock in it). If exhaust is getting into the cooling system, the coolant usually ends up smelling of exhaust.

If the HG leak is between the supply oil-way (in one corner of the HG) and one of the HG coolant openings, engine oil can get injected into the cooling system (it's under much higher pressure than the coolant), and you will find oil floating on top of the coolant in the header tank. It doesn't sound as if you have this.

Both of the above will cause repeated coolant loss (not to be confused with just over-filling) and erratic behavior of heater and thermostat.

[August]

So it is most likely a blown head gasket?

[xantia_v6]

On a petrol engine, the combustion pressure increases with the load on the engine, and a small gasket leak may not be obvious at idle.

You can probably buy a kit to test for combustion gasses in the coolant.

[August]

But if the pressure is building up in the coolant system from just a minute of idle, doesn't it make it quite obvious that the HG is leaking cylinder pressure in to coolant system? Because im pretty sure it shouldn't start building pressure untill it gets up to tempereture

[white exec]

Normally, pressure will not build up in the cooling system after just a minute of idling, or even a few minutes. For pressure to build, the coolant temperature will need to be quite high.
It does sound as if your HG is leaky/blown.
A workshop would be able to do a compression test on the engine (via the spark plug holes).