Hi Roger, Thanks for the useful information, I haven’t done the hose test yet but I do have a aftermarket aluminium rad fitted, does that make a difference at all.
I have a suspicion that the more efficient aluminum rads have the potential to mess with the normal cooling dynamics on cars with thermostats on the cold side of the radiator, particularly on the smaller engined/lower powered cars that produce less heat output.
Unfortunately the Duratec has the stat on the cold side of the rad unlike older generation cars with the stat on the hot side of the engine. On older cars the the stat was opened simply by the heated coolant exiting the cylinder head. Cold side stats are opened with a combination of hot bypass coolant recirculated through the engine and the cooled coolant exiting the rad. These two coolant paths merge within the stat housing and the resultant combined coolant temp sets the stat opening point. That's fine until the balance is upset with cooler coolant from a more efficient rad. Then the combined coolant temp will be lower and the stat no longer opens at the same point as before. It's totally counter intuitive but a bigger better rad may actually make a car run hotter rather than cooler and also make a car run hotter when the ambient temp is lower on a cooler day.
I very much hope I'm wrong with this but it might be worth trying your bypass test or even just checking when you hear the fan come on by feeling the bottom hose to see if its cool indicating the stat is shut. Normally the stat should be fully opened when the ECU triggers the fan and the bottom hose hot. And yes the Duratec will actually run with the stat closed with the bigger ali rad. It appears to derive a modicum of cooling from the coolant flow through the small bore pipe that short circuits through the header tank and the rad top header. Something that I suspect might go unnoticed.
