Intermitant Over Heating 4.6?

Hi All,

Im Hoping this isnt going to be a cracked block, so im going to ask you all and hope there could be something im missing.

Ive just done the head gaskets on my dads 4.6 2000 p38 after it boiled up the other week. took me a day to strip then another day to put back together after getting the heads skimmed. the car was running like a dream. I took it out the other day for a long run, hot day no problems. sat in traffic no problem, then about 50 miles on the motorway and ran fine.. I got it home, sat in the house for a couple of hours popped back out, did about a 5 mile drive when i noticed steam under the bonnet. opened it to find a split in the top hose and steam coming out.. The hose wasnt the best when i put it back on so orded one but not arrived yet.
i went to pop the lid of the expansion tank and alot of steam bubbles etc. I let her cool down, topped her full of water the following morning so i could have a look in the light and nothing. running like a dream. no pressure, no steam nothing???? im at a loss. I have checked the water for exhaust gasses and nothing????
anyone any other ideas..
has anyone had this???
Is it just havin a bad day???

not sure where to go from here?
Your Thoughts Please

air lock when you fit new hose, dont forget to turn heater on full hot when you bleeding it..

have you checked rad is hot all over and so cooling effectively all hoses get hot including heater showing flow ,thermostat opening hot both side of housing,was drivers side the one you thought head had gone on ,the only way to prove,cracked block unless gone so far that it becomes obvious is to strip heads off front cover off block water ways and fill with hot water and pressurise block with air ,if cracked it will bubble up between liner and block

Pressure in the header tank and firm (but not solid) hoses are normal and are all part of making sure the water doesn't boil too easily.
Folk far wiser than me would probably be able to explain it but I think water under pressure has a higher boiling point and some pressure is actually required for a cooling system to work.

Thanks for the help..

Ive been looking aound the last couple of days and all seems to be well.. i hoping that i just missed a bit of air in the system and as a result it was just boiling it through a gap..

I ran it again with the heater on full and fingers crossed. think im still going to take the rad's off next weekend and give it a good clean out befor my old man gets it.

j the range said:

air lock when you fit new hose, dont forget to turn heater on full hot when you bleeding it..

Click to expand...

All p38a and classics are constant flow heater matrixes!
I would be inclined to take the little pipe off to the header tank from the rad and insure it has flow.
Not uncommon for the thermostat to fail or it is wax state cap stuck closed, again getting coman with age on the p38a
Was the pump ok had one do this and found the impeller had fallen off!