i might missed it, but all radial engines in CoD need a engine cylinder temperature (not oil !) of minimum 200° .
Than, then the Blenheim flys ok
The gauges are:
in the Blenheim right behind your right shoulder, over the fuelcock wheels
in the FIATs they are on pilotpanel, one have just to select a cylinder to get a temp reading, by default it is set to "none"...
Sidenote about the G.50 gunsight - set your gunconvergence to 200m (default is over 300m IIRC) , than the tracers fly in line