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Ask Dominick Your Own Question
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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My 1998 60hp Johnson over heats above 4500 rpm have changed

Customer Question

my 1998 60hp Johnson over heats above 4500 rpm have changed water pump impellor and sensor removed thermostat had it in two shops.
Submitted: 2 years ago.
Category: Boat
Expert:  Jeff G. replied 2 years ago.
Hi, what did the two shops do? When the pump impeller was replaced were the gaskets replaced? The thermostat is in a carrier, are you running with the carrier. What kind of temperatures are you running? Is this a new problem or did it come after sitting or repairs?Are you getting a good solid stream of water from the tell tale when at cruising speed?
Customer: replied 2 years ago.
shop used impeller kit thermostat carrier in place problem started while returning from 10 mile run compression and leak down good water stream good carburetors set right motor temp running with hose was 160 after removing guts from thermostat 98
Expert:  Jeff G. replied 2 years ago.
So when does the engine overheat? Are you checking cylinder head temperatures at the thermostat housing when it overheats? Is the thermostat carrier diaphragm in place?On the hose in neutral even 160 is high.I think you may have a restriction. There are two common areas for restrictions, the adapter plate under the engine. There are pockets that can collect mud and debris. The other place is at the top of the water tube. There is a rubber grommet. If the engine got hot enough it could have partially melted of softened this grommet and it can block the flow of water into the engine. It won't block all of it but enough to cause a flow restriction and overheat at higher speeds.The adapter plate is #13 in the drawing and the grommet is #21.You will need to pull the powerhead to get to and examine both of these. You'll need new gaskets for the adapter plate.