I bought a Peugeot 406 and discovered a leak in the radiator hose so i replaced the hose and now i find there is a build up of pressure coming from somewhere which is causing a hissing noise even when the engine is just ticking over. I have replaced the thermostat but this doesn't seem to have helped any ideas welcome??
looks like your head gaskets gone mate.
remove cap to release presure, replace cap and rev engine for a few secs.
stop engine a release cap again slowly if there any pressure your head gasket is leaking.
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