Re: 496 Mag HO water circ. problem
 

If you have the older 496 Ho and have not had the water rails changed (recall) this might be part of the problem. There is a problem with the Brass Elbow and the water rail, unlike metals and tend to corrode. Just had this done last week.

KB

Re: 496 Mag HO water circ. problem
 

Thanks, I am almost positive the rail has not been changed (boat is new to me). The motors are real early 496 models. I plan on calling and asking about any and all recalls on my motors this week.

Thanks again,
Bill

Re: 496 Mag HO water circ. problem
 

I installed the J+P brand flush valve on my ho's. I installed them in the main inlet hose between the drive and c-pump. Installed a perko hose mount and a hose to top of the valve. When I flush my boat out on the lift (POWERQUEST 340 Vyper), 1 engine
at a time I never have a problem with circulating water. Reacts as though it was in the water.

Re: 496 Mag HO water circ. problem
 

Does this engine have the power steering pump?, 10 degrees higher would be about right.

Re: 496 Mag HO water circ. problem
 

same problem on a hose... but when the boat is in the water... works fine...
I did it on the hose this spring and shut it off about 6 times before i let it go long enough to come out the exhaust...

Don

Re: 496 Mag HO water circ. problem
 

May not be right, but here is what I have come up with. I think the drain valves (for winterizing) are letting air by. I have noticed water draining from the water pickups for a long time after putting on the lift. Also it takes a long time, sometimes it takes revving to prime the pump. Once primed everything is fine. Looking at my water pressure right after starting is near zero (not always, but usually), once the prime is caught the pressure usually runs between 3.5 and 4 pounds at idle. It is impossible for water to make it back past the water pump impeller which would also not allow water to drain unless it is getting air from somewhere. I am not interested in replacing my drain valves, so for now, I am going to rev it a little (1500 approx) to get the party started after I am comfortable with oil press, etc after starting.

Any opinions?

Bill

Re: 496 Mag HO water circ. problem
 

replaced this pump

Possible Air Actuators
 

Working on a 2003 that has the air actuators for winterizing. Vessel was brought to me after another shop replaced the impeller and still had overheating at the manifolds and no water flow. I still have yet to contact mercruiser on this issue. So far I found that if I remove the black air lines to the top of the air actuators on port and stbd side of the engine the water flows perfectly. There is a code and the engine is in guardian mode. Possibly the sensor on top of the plenum is faulty not letting the vacuum move the actuators. In this specific case this is where the problem is and why there is no water flow. I will follow up with the outcome when the job and research is complete. 2003 496 Mag HO close cooled.