P38 Coolant Pressure

I wonder if anyone can help. I'm trying to diagnose why the coolant is sometimes blowing out of the expansion tank. How hard should the top hose be when the engine is hot? Basically i'm trying to establish if it's an engine fault or cooling system fault. I'm waiting for delivery of a new Rad after fitting a new thermostat, and viscous fan.
The car drives perfectly for aronud thirty miles then oops up goes the gauge and wonderful steam.
I've recently moved from England to Sunny Corfu where the temp is alot hotter, and i'm wondering if the increase in ambient outside temp is affecting the car. Is it possible that it could be something simple as the pressure cap.
Anyone's thoughts would be appreciated, as i'm fed up with my eyes fixed on the temp gauge instead of looking at the beautiful views of Corfu.

If you are getting an increase in pressure in your water system then there is a possiblity that you have a blown head gasket, the compression pressure from your engine is being forced into your water ststem and this is causing the blow back.
Have you tried removing your thermostat completely and allowing your engine to run cooler and have a constant flow through your rad?

Thanks for that Simon however i have had the expansion tank sniff tested and given the all clear. I realise that this test is not 100%, but the car in my experience is running to well to be the head gasket's. As far as the thermostat goes on the P38's its built into a housing that connects four pipes to it. So removing it is not an option, however I have shall we say destroyed an old one by smashing the inside with a screwdriver so the stat is open all the time and fitted that to the car with no change.

corfunightmare said:

Thanks for that Simon however i have had the expansion tank sniff tested and given the all clear. I realise that this test is not 100%, but the car in my experience is running to well to be the head gasket's. As far as the thermostat goes on the P38's its built into a housing that connects four pipes to it. So removing it is not an option, however I have shall we say destroyed an old one by smashing the inside with a screwdriver so the stat is open all the time and fitted that to the car with no change.

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a very easy check that you can do is the bleed pipe from the top of the radiator to the header tank , remove it and check for blockages , this will cause serious circulation problems if blocked , dont forget to check the nipples that the hose is attached to as these also block up this is fairly common problem on the p38 and worth checking.
rick.

Thanks Rick I have already tried this, however i didn't check the nipples. Mind you as i said i'm waiting for a new Rad so this would resolve that one. Whats your thought's on the expansion cap, could this be a problem?
I suppose really I'm thinking its a head off job and i'm trying to delay it, it's just that the car is driving so well. Any car i've had before with a head fault you knew it.
Anyway thanks for your help mate appreciate it.