Re: 7.4 overheating
I just bought a 1991 searay cc with 7.4 mercruiser with bravo. Boat was apparently winterized last season (guy gave me receipt) Put oudtrive on and two new batteries. Fired boat up, and noticed no water coming out of the exhaust. Changed the water pump and had good flow coming out the back of boat. Boat ran about 10 min on the ear muffs and the temperature started climbing and reached 210 before I shut it off. We changed thermostat prior. The housing was cleaned out. A piece of that housing is cracked where those balls are, but does not appear to affect the flow. Prior to this when we first ran motor with no out drive on and water directly into the port the port side riser was cool to touch and left side was hot. Now after, new water pump, new thermostat both sides are running hot. Any suggestions. My buddy said that the manifold and risers look fairly new, but not 100% sure how old they or the actual maintenance of boat. Oil appears to be clean.
When you say "water pump", you talking about the "engine water pump" on the front of the engine or the "raw water pump" mounted low on stbd side with the fuel pump?
Is the temp actually 210 deg? Is temp gauge accurate? If you have good flow out back, the stat could still be kaput and water would bypassing engine and going straight to the risers. You could pull stat out and see if engine heats up at all. That engine should be running around 160 deg while cruising along, as my 7.4 does. Tends to run cooler on hose, due to the cold well water.
With the hose going to power steering cooler disconnected, that pump should move about 7.5 qts of water in 15 seconds, running at 2,000 RPM. When installing the the impeller for the raw water pump, looking at the engine from the front, the pump turns clockwise. You can disconnect pump belt and water outlet hose and with garden hose attached and charged, turn pully by hand and water will come out of discharge port of pump. Was the impeller twisted into the housing so that the vanes "lag" the impeller hub when it's turning the correct direction? Was the raw water inlet hose (from the transom) installed to the upper nipple on the pump and lower nipple (pump discharge) goes to power steering cooler.
I'm asking all these questions, because this is stuff I have seen folks do before and I had to correct.
My port riser got very hot also and it was the check ball in the housing, going to that riser, was stuck in the bore, shutting off cooling water. Cleaned it and cleaned out the scale and all was good after that. Have you had the risers off and actually looked at the water passeages in the risers / manifolds? They can look brand spanking new on the outside and still be all clogged on the inside if someone never flushed the engine after use in salt / brackish water. Or maybe someone put the wrong riser gaskets on when re-assembling. Sometimes the simple / most obvious stuff will bite you, but ya gotta start somewhere (work starting at the cheapest and work toward the expensive if troubleshooting is in-effective). Hydro-flow can be very baffling at times.
