This will probably start something.
First of all it depends on what you are starting with. We will eliminate engines that have been torn down, cleaned and rebuilt.
An old engine that has set for a long time but is supposedly in running condition. I like to run them if possible to evaluate before restoration starts.
Drain the oil. If it has a filter, change it. Refill with a HD multi weight. (lube the cylinders and make sure it has coolant)
Run the engine until it is warm (10-25 min.)and do the evaluation.
Drain the oil as soon as the engine stops and replace the filter. Inspect the oil and determine if it is slightly dirty, very dirty or gross.
Slightly dirty - repeat the process but run for 30 min high and low RPM's and check the oil again. If it still looks good you won the lottery.
Assuming that you aren't planning to pull the engine down (or we wouldn't be having this discussion)
Any of the others- Remove the oil pan and clean. Same with valve covers or lifter covers and clean out all you can.
Reassemble, fill with new oil and run for 1/2 hr. dump oil and filter. Refill and drive for 100 mi and dump oil and filter again. Depending on how good or bad the oil looks repeat at 500 mi or 1000 mi then go the usual change schedule.
I never recommend using engine cleaners. If Hot HD oil doesn't remove it, leave it alone.
