I'm not a mechanic but hypothetically you may have a warped head which is causing air to get into the cooling system. This air is finding it's way to the top of the system and sooner or later getting into the thermostat housing. With some air going through or remaining in the housing the thermostat will take longer to get up to temperature and activate the cooling system which would explain the delay in the fan spinning up. If the thermostat housing completely fills with air the thermostat may not get to temperature to open the cooling system at all causing the local coolant to boil and pressurise leading to it being forced out of the system, which would explain your scalded leg.
You're right though that this doesn't explain why the multiguage isn't picking up the temperature reading as it should. I would contact Christian and see if he is able to make any suggestions, he was active on these forums a while ago and is very helpful. I assume you bought the multiguage direct from Christian so can lay your hands on his contact details.
You're right though that this doesn't explain why the multiguage isn't picking up the temperature reading as it should. I would contact Christian and see if he is able to make any suggestions, he was active on these forums a while ago and is very helpful. I assume you bought the multiguage direct from Christian so can lay your hands on his contact details.