496 HO water circulation issue

[PQvyper340]

Before I put my boat away for the winter I started both motors on muffs. Started w/the stbd motor then the port. Then went back and started the stbd motor again to check something and now the 2nd time I started it there was no water coming out of the exhaust. Figured, no problem, I was going to rebuild the water pumps over the winter anyway. Well, the impeller looked fine. I rebuilt both of the pumps (hardin marine sea pumps) anyways on both motors (02 Powerquest 340 w/496 Mag HO's). Went to start it on the muffs a few days ago, port side motor started pumping right away, no problem. Started starboard side motor and nothing, let it run for a minute or so and still nothing. Tried reving it up a little, nothing. I even took off the muffs and put the outdrive in a big 100 gallon trough, still nothing. Any ideas? I also cleaned out/serviced the heat exchanger over the winter, so I know there is no blockage in there.

I took the hose off of the transom assembly and ran water down through the drive to make sure there was no obstruction. I then pulled the hoses off the back of the water pump, there was water in the inlet hose, but none in the outlet hose (totally dry). I took the raw water hose off of the inlet side of the heat exchanger and tried backflushing through the system so that water would come out of the outlet hose to the water pump but couldn't get any water to come out. Not sure if I just don't have enough water pressure or if there could be an obstruction somewhere. Although, if there was an obstruction I would think that the outlet hose coming off the back of the water pump would have at least some water in it (unless if it self drains). I boat in clean fresh water.

I'm just totally stumped and I really don't want to take everything apart (I think I'd have to pull the engine to check for obstructions in the fuel cooler and oil cooler). Any suggestions?

 

[alldodge]

Before I put my boat away for the winter I started both motors on muffs. Started w/the stbd motor then the port. Then went back and started the stbd motor again to check something and now the 2nd time I started it there was no water coming out of the exhaust. Figured, no problem, I was going to rebuild the water pumps over the winter anyway. Well, the impeller looked fine. I rebuilt both of the pumps (hardin marine sea pumps) anyways on both motors (02 Powerquest 340 w/496 Mag HO's). Went to start it on the muffs a few days ago, port side motor started pumping right away, no problem. Started starboard side motor and nothing, let it run for a minute or so and still nothing. Tried reving it up a little, nothing. I even took off the muffs and put the outdrive in a big 100 gallon trough, still nothing. Any ideas? I also cleaned out/serviced the heat exchanger over the winter, so I know there is no blockage in there.

I took the hose off of the transom assembly and ran water down through the drive to make sure there was no obstruction. I then pulled the hoses off the back of the water pump, there was water in the inlet hose, but none in the outlet hose (totally dry). I took the raw water hose off of the inlet side of the heat exchanger and tried backflushing through the system so that water would come out of the outlet hose to the water pump but couldn't get any water to come out. Not sure if I just don't have enough water pressure or if there could be an obstruction somewhere. Although, if there was an obstruction I would think that the outlet hose coming off the back of the water pump would have at least some water in it (unless if it self drains). I boat in clean fresh water.

I'm just totally stumped and I really don't want to take everything apart (I think I'd have to pull the engine to check for obstructions in the fuel cooler and oil cooler). Any suggestions?

:welcome: to iboats

There are some variations to the 496 cooling system. What is your engine serial number?

 

[Bondo]

Before I put my boat away for the winter I started both motors on muffs. Started w/the stbd motor then the port. Then went back and started the stbd motor again to check something and now the 2nd time I started it there was no water coming out of the exhaust. Figured, no problem, I was going to rebuild the water pumps over the winter anyway. Well, the impeller looked fine. I rebuilt both of the pumps (hardin marine sea pumps) anyways on both motors (02 Powerquest 340 w/496 Mag HO's). Went to start it on the muffs a few days ago, port side motor started pumping right away, no problem. Started starboard side motor and nothing, let it run for a minute or so and still nothing. Tried reving it up a little, nothing. I even took off the muffs and put the outdrive in a big 100 gallon trough, still nothing. Any ideas? I also cleaned out/serviced the heat exchanger over the winter, so I know there is no blockage in there.

I took the hose off of the transom assembly and ran water down through the drive to make sure there was no obstruction. I then pulled the hoses off the back of the water pump, there was water in the inlet hose, but none in the outlet hose (totally dry). I took the raw water hose off of the inlet side of the heat exchanger and tried backflushing through the system so that water would come out of the outlet hose to the water pump but couldn't get any water to come out. Not sure if I just don't have enough water pressure or if there could be an obstruction somewhere. Although, if there was an obstruction I would think that the outlet hose coming off the back of the water pump would have at least some water in it (unless if it self drains). I boat in clean fresh water.

I'm just totally stumped and I really don't want to take everything apart (I think I'd have to pull the engine to check for obstructions in the fuel cooler and oil cooler). Any suggestions?

Ayuh,..... Disconnect the hose where you can get at it, that comes From the coolers,.....

Disconnect the hose goin' To the coolers,...

If yer hose water doesn't freely flow through from one end to the other, in both directions,.....
I guess yer gonna have to do whatever it takes to pull the coolers, 'n clean 'em out,.......

My guess is, ya got a blockage somewhere in the area I underlined in yer post,...
I also think ya oughta rebuild the pump again, as it sounds like ya ran it dry, for awhile,.....

For back-flushin' out to the drive, do that from the raw water input hose,...

 

[PQvyper340]

I will check the serial number when I get home later. I know it's one of the earlier 496 HO's. Also, I just realized that when I was trying to backflush I was using the wrong hose off of the heat exchanger. I was using the one that goes to the exhaust manifold... I will try the other one later today and see what happens.

 

[Fun Times]

Hi there, welcome to iboats!

While the water drain system is hard to see on your engine, a mirror would help. Down low on the portside behind the serpentine belt area is your water drain assembly that should have a blue plastic drain plug that you can pull to see if you are getting water down in that area. It's next to.. but way before the cool fuel pump. It's between Item numbers 12 & 13 (< scroll down to the next diagram) http://www.mercruiserparts.com/Show_...4+and+Below%29

# 1 is the drain & 5 is the blue plug, http://www.mercruiserparts.com/Show_...R+DRAIN+SYSTEM

PS, do you have a Bravo 1 or 3? If B1, you'll need to know if you have both low water and side water pickups. If you have both, you'll need to put some duck tape over the low water pickups at the nose of the lower gear housing to avoid sucking in air.

 

[PQvyper340]

Well, after all this I might just be an idiot...lol. I took the water pump apart last night and apparently I did not put in the front (toward pulley) wear plate. I haven't re-installed the pump yet but hopefully that will take care of it. I'll be installing it and firing it up later today.