Will mondeo st 24 2.5l 24v engine fit in same age cougar.

As Tony and Paul recently found out, the only difference is a knock sensor. The Cougar has one but the Mondeo doesn't. And the Mondeo engine doesn't have a hole with the correct thread to fit the sensor.
I think they found a workaround but I'll leave it to them to post details.

Otherwise, a Cougar sourced engine won't have this issue.
Make sure the donor engine had the same transmission as yours. ATX and MTX crankshaft splines are different. The end with the splines can be swapped but as the Mafia told me, it takes a lot of bute force to change them.
 
Its not splines Manos, its a sodding great bush lol and its a tight fit!!!!! lol if engine comes from an auto it just needs to be removed to fit a manual box ;-)

Mongy lump can be converted to take a knock sensor by tapping the M10 hole out to M12 then getting an adaptor made from M12 to M8 and threadlocking it in ;-)
 
Its not splines Manos, its a sodding great bush lol and its a tight fit!!!!! lol if engine comes from an auto it just needs to be removed to fit a manual box ;-)

Mongy lump can be converted to take a knock sensor by tapping the M10 hole out to M12 then getting an adaptor made from M12 to M8 and threadlocking it in ;-)

why cant you get an adapter made from M10 to M8 :p
 
if you have a M10 insert/adapter by the time you drill and cut a M8 thread,there would be little or no material left to be of use, due to the depth of the M8 thread that has been cut, by taken the original out to M12 the M12 insert/adapter wall is thicker to allow this to happen, if that helps or might of just confused it