The 3116 in the higher hp range was a real problem child for Cat. The 3126 seemed to escape many of the problems. As with any engine it needs to be maintained and run properly. With these two engines valve lash and timing are important and require a special set of tools to do the job properly. Due to the cost of these tools many independant techs don't have the tools to do this job. If you can do a sea trial on the boat a few things to look for before you get a good Cat guy to look things over, make sure the engine turns up to rated RPM and take note of the amount of water, fuel and gear on the boat. Look for black smoke when running. Make sure the temperature stays fairly steady form cruise to WOT and does not rise above 200 degrees. Look at the exhaust water at start up and when up to normal temp for oil in the water. Try to find out where the engine was run for most of the hours, idle, cruise or both.
I know of a few lobster boats that have them and get 5 to 7K hours no problem.
