When does a diesel reach full operating temperature?

Reading thread 35643 made me wonder how long it takes to reach full operating temperature in a diesel. I've always used about 20 minutes as a yardstick to get everything fully stabilized to the normal operating conditions (whatever normal may be). Clearly this will vary enormously with engine size, and duty cycle. A chain saw will be fully stabilized quickly, while a 15,000HP ship engine might take a little longer. A fully loaded engine will reach a higher stabilized temperature than a lightly loaded one.

I remember doing some performance benchmarks on a Cat 789 rear dump at Ok Tedi mine in PNG. Part of the work involved measuring haul cycle times. We did several cycles in succession from the start of shift (cold engine)...and about 15 mins run to the starting point. The haul times continued to improve over the first 3 cycles (about 12 mins each) then stabilize. So, I suppose optimum operating conditions were achieved in about 50 minutes for that engine.

As far as warming up before you drive off goes, I don't see a lot of benefit in long periods of idling to pre-warm the engine. I'm happy to get the oil up (while I put on the seat belt) and drive gently for maybe 5 kms. All the running gear is still cold until you start driving anyway.

More recently I did some tests on some Cat 440HP engines powering water pumps on a cotton property. The worker helping me idled the engines until he could feel the cylinders warm up and then open up the valves to pump water, and load the engine up. About 5 minutes max probably. If they had them all running at the same time, there could have been 30-40 pumps running...and one bloke to start them all. About 8 engines per pump station, so it may have just worked out this way. Once the last engine is started the first can go to work. Not sure whether there is some compromise in this case, or not.

Be interested to hear others comments.

Regards
Brid