LowNSlow, I see that many moons ago you asked about warming up big radials. The principles are the same as with any piston engine, but you do have to be very thorough with the procedures or significant mechanical damage will occur. My comments below relate to the PW R-1340 engine in the Harvard and the PW R-2800 engine in the Hellcat and Corsair. Other combinations, such as the Centaurus engine in the Sea Fury or R-2800 in the DC6, may be markedley different.
After starting with cold oil, the oil pressure will initially be very high, with a quoted maximum limit for most engines of 100 psi. With the PW R-1340 you can keep the pressure down to 100 psi by running at around 700 - 800 RPM then, as the oil temp increases, progressively increasing the RPM to maintain 100 psi until the normal warm up setting of 1200 RPM is reached. With the PW R-2800 you may see pressures as high as 200 psi after start. Pilots' Notes states that the RPM must not exceed 1000 until the oil pressure is less than 100 psi.
As with most engines, the RPM must not exceed the "warm up" setting (1200 R-1340, 1000 R-2800) until the oil temp reaches 40 deg C and the CHT reaches 120 deg C. This inevitably precludes taxying on grass but should allow you to taxy on hard surfaces if reasonably level. Also, although it may seem logical to warm up the engine with the cowl gills closed, in the Hellcat this can cause heat damage to the ignition harness so they must stay open on the ground.
Some engines have a lower maximum CHT limit on the ground than in flight, presumably due to the reduction in cooling airflow to certain cylinders without the airflow into the cowling.
Big radial engines do not like sudden large temperature changes. Therefore, you do not go straight from a display (continuous rich) setting to very low power for the approach. You always aim to spend a few minutes at a cruise power setting before an approach to land to let the engine temperatures stabilise at a lower value.
Prior to shutdown you run the engine at 800 - 1000 RPM for at least a minute to let the temperatures throughout the engine stabilise. Also, there is a maximum temperature for shutdown which is less than the normal ground maximum temperature. This is because the CHT initially rises after shutdown due to the loss of propwash over the cylinders.
So far on this thread, no-one has mentioned the problems of warming the engine in flight if the CHT cools below the minimum value. In the Harvard, this occurs easily during prolonged flight at idle (stalling, spinning, high speed dives), and I have often seen it with the IO-540 in the Beagle 206/Basset during descents and after engine shutdown during airtests and training. If you fly an aircraft that is prone to this and the POH does not tell you the power setting for warming up, you must use the minimum power that will give a CHT increase without losing too much altitude. Work it out in advance, remember it and use it!
I was somewhat alarmed when I first read this thread that minimum oil and cylinder head temperature limits were not being strictly adehered to. This comment is not a criticism of those who have posted here. In fact, it was heartening to find the interest in researching this field. However, it does raise two questions in my mind. Firstly, are POHs adequate in the promulgation of engine limits and advice on how to adhere to them? Secondly, is engine husbandry emphasised adequately during PPL training by flying instructor? I suspect that this might stimulate more debate!
Hope that this is of interest.