I have the same issue with this mission... the Thermal Sight is not showing the engine block... the entire vehicle glows as a hot spot. You have to practically stand on the vehicle for the Thermal Sight to differentiate and display heat variance.
I turned off all my mods crawled inside of 100m's of this vehicles... and still can't tell where the engine is... the entire vehicle is glowing white hot. It's a good premise for a mission, but it's completely irrelevent if the Thermal Sight isn't working well enough to do the job the mission is based around.
Where am I supposed to shoot this BDRM exactly?