I would agree with the posts above that this is a water/coolant issue rather than oil. What was the water temp (if there is a guage) when the alarm went off? I would determine if you are getting enough raw water flow through the exhaust and also check your coolant level. I always change thermostats if an engine overheats, and changing the impeller on the raw water pump, or at least checking it would be a good idea.
SV Laurie Anne
1988 Brewer 40 Pilothouse