I have been asked several times what should be done when buying a used outboard motor. Most all will tell you, compression tests, leak down tests, pull lower unit, oil samples, check lower unit oil, check exhaust ports and so on. These are good things to do. You also can pull an engine anode or two and scope the condition of these cooling areas. Pulling the thermostats and boring scoping that area of the head will tell the story of that very important part of the engine. It will tell you the story on how well that owner flushed and or did not.
Here are some pictures of thermostats. We serviced these outboards and changed the thermostats. This Set of 250 HP outboards had 600 hours of use. These should have been checked and or changed long before now but the owner stated it was a fresh water set of engines and did not need it. Supposedly these motors had 500 hours of fresh water use and 125 hours saltwater use.
Of the four thermostats pulled, two were badly saltwater corroded and one was stuck open. It was caught in time and the bore scope showed a pretty good clean surfaces inside the engine. The thermostat housing area had to be cleaned up due to saltwater allowed to rest in these areas. Better flushing would have helped. No harm, all look good but thought this blog would help others.
Check those thermostats and flush those engines after saltwater use.
I showed a new thermostat here for ref. The housings cleaned up nice and no surface area damage. If allowed to go on, you can damage the housing area and surface areas around the cylinder causing water ingestion.