I know you are a Mercury man, but I have a question about 60 HP 1997 Yamaha that you might shed some light on. I am told that this engine will not register water pressure accurately at WOT. At idle it is 3 psi, during acceleration ii is 18-20 psig and at WOT it drops to 5 psig. I'm told these engine have always done this. Engine does nor run hot. New water pump, thermostat, engine flushed thoroughly. Have you ever seen this before? Thanks for your help.
Humminbird
Honestly, I'm NOT a Yamaha man. Really not qualified to answer the question.
In general theory.... a drop in water pressure at WOT (over mid-range) is an indication that the cooling media being supplied to the water pump inlets (at the gearcase) may be AERATED (inadequate cooling media being supplied).
This can be caused by too high an engine mounting height, excessive trim angle, objects FORWARD of (within 12" side to side) of the gearcase disturbing or aerating water flow (transducers are often the cause), etc. etc.
Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
Still consider myself a "Marine Apprentice" after 48 years (learn something new every day).
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