Not well up on these, just suggestions.
After 10 mins, or so. It will be up to temperature, after 1/2 hr. it will be below temperature. Some have temperatur sensors/switches to change things after warmup. ie my boat diesel engine, has a temp switch. for the injectors, auto advance for after warm up, It will switch the injectors to a different setting. Also has an auto idle temp switch, which keeps the revs that bit higher while warming up, once warmed up, switches high idle off. I think you need to look for something along the same lines. Look for sensors/switches in the engine block. Maybe while doing clutch, a wire has been left off, or was loose and come adrift. 1 of my switches, is situated just above the starter. the other at the front, in the water feed sections of the block. Hope this helps
SD
May 2012