inspecting mercruiser outdrive oil

Question
QUESTION: I recently bought an 84 Sea Ray with a 5.7L Mercruiser.  I am draining the outhdrive oil and am wondering how to tell if there is water in it and what color it should look like.  The oil is dark brown, not black

ANSWER: Hi Jack...Thanks for selecting the undersigned to reply to your question.

Water-contaminated oil will look grey or milky. A slight grey tinge indicates a small amount of water contamination. Milky oil suggests the possibility that bearings and shafts might be affected and begin to rust. In addition, the lower unit will heat up quite quickly and often begins to smoke.

Safe Boating
Ron

---------- FOLLOW-UP ----------

QUESTION: Thankyou for the information. Also my 5.7 Mercruiser seems to overheat at idle, but if i run at 2000 RPM or greater the temperature drops immedeatley.  Any thoughts?

Answer
Jack, best you check the condition of the impeller, located in the lower unit of the sterndrive. This is what draws in fresh water that circulates throughout the water journals of the engine block to keep it cool and prevent seizure of the pistons.

When the rmp's are increased, it suggests the impeller's rubber blades may be badly worn, and it's time for replacement. Or, there might be some foreign matter in the fresh water intake/impeller housing that is restricting the flow of fresh water to cool the block. Best you consult a qualified and reliable marine mechanic to diagnose and resolve the problem asap.

Safe Boating
Ron