Overheat WOT

"Hello Everyone,
I started to

"Hello Everyone,
I started to have a overheating problem last summer after I replace the engine. the problem started mid way in the season. when I ran the engine at the RPM 3000-3500 the engine temp stayed 150 and below. when i moved up the RPM to 4000 engine temp would shoot up to 180 - 200. as soon as lowered the RPM back down to 3000 range temp came back down to normal.

engine is mercruiser 5.0L v8 carb new drop in.
outdrive alpha 1 gen 2 hoses and water pump all replace two years ago...

Not sure where to start looking for the problem"

"Christopher,
A high speed ov

"Christopher,
A high speed over heat is usually a sign of the water pump impeller starting to wear. As the pump spins at full speed water will slip past the tips so you are not getting the full pressure."

"Start with a new impeller, st

"Start with a new impeller, standard life is 2 years, water pickup hose could be getting kinked a bit, might be sucking air from the pump, thermostat restriction,clogged riser/elbow(s), flapper in the Y pipe dislodged and sitting in the Y pipe."

Simplest and cheapest is a new

Simplest and cheapest is a new thermostat.

Change that first.

Are you cooling with raw water or closed system?

If you are cooling with raw water in salt water
you may have corrosion in the exhaust and its blocking
water flow.

Run with someone else running boat and feel where
the heat is coming from.

--cal

"My nickle's worth:

If

"My nickle's worth:

If you have access to an infrared heat gun that is a great way to tell if anything is overheating while someone else drives.

Brians advice about changing the T'stat is a great place to start. Impeller next, especially if its older than 5 years or 250 hours, or if you have ever run it dry.

Rod"