When I operate my mini hyds, the cyls are always moving so oil flow is not deadheading thru the relief valve to return to the reservior. That trick saves on amperage consumption & helps to keep the oil temp lower.
My dozer would be the only model that the cyls are not constantly moving, oil flow would be straining thru relief valve for possibly as long as 30 sec intervals without cyl movement... however, the pump psi was never changed from factory setting (10bar) & it's still the original to the model circa 2002.
I saw in a Tower Hobbies e-flyer this infra red temp tester, it crossed my mind briefly whether to get it or not for just such a job.
http://www3.towerhobbies.com/cgi-bin...?&I=LW6004&P=E