P38, 4.6 Intermittent overheating

Help Guys before I go mad!!!
Replaced the engine with a new short engine in my P38 six months ago because of a porous block. Motor ran like a dream for about 3 months then whilst stuck in traffic-temp. needle went into the red. Checked water level-no loss. drove home and car was fine for a week then got hot whilst driving. Replaced Thermostat thinking it may have stuck-same thing happened later. Replaced Viscous coupling-same thing. Replaced temp. gauge sender and ECU temp. sender-same thing. I am not losing a drop of coolant. A new water pump was fitted when the engine was rebuilt and radiator fins were pressure washed. The water passageways in the heads were spotless (I have always used 50% anti freeze mix). I never had an overtemp problem with the old engine until the block went.
One question-the Condenser fans do not seem to be cutting in either for the aircon or when the engine is hot, yet I can "Force" them on okay with Rovacomlite which confirms that the relays etc. are okay. Any advice before I go and buy a new radiator, which is the only thing left to change.
By the way-I do not have the "Cheque Book" symbol on the HEVAC display and the aircon seems to be working fine.

i had a intermittent cooling problem which was causing me headaches and seem to try everything when someone suggested bringing the engine up to temp then feeling the fins on the rad once the engines off to see if i had any cool spots which i did have (meaning i had blocked fins causing it to pressurize the system) so i replaced it with a new one and so far 3 weeks on its working fine
i know your pain stick with it

Andy

Thanks Andy
I have not managed to feel the rad. as you have done-with the aircon. condenser in front and the fan behind, it's difficult to get access. However what you say makes sense as when she's hot, the top hose is rock hard. I have felt the top and bottom tanks of the rad. and they are both the same temperature.
And Yes-I have blown through the bleed pipe from the top of the rad. to the expansion tank in case that sugestion crops up.

Cheers Guys

99.% radiator when we build these engines we have the rads flow checked if they operate at anything less than 90% we change them as we have learnt our lesson the hard way.

yes there isn't alot of room to get to feel the rad but i unclipped the cover at the top of the fan and just had enough room to get my hand in an move it about to feel the fins

Hi Guys-fitted a new Rad.-problem solved. Wouldn't have thought it,
looking into the top hose outlet on the old one it looked clean but obviously one or more of the tubes were restricted.

Great stuff!!!