Mercruiser risers

I also would pull a hose from a riser and see if it will pump into a bucket. There should be a Merc spec for that flow rate but any good stream would likely be fine. If not, look for a blockage at inside and exterior (thickly painted over?) intake strainers, oil & trans. coolers & H/ex. and maybe try backflushing each section into a bucket to check. Was there noticeable flow before the riser replacement? If you check the impeller and it looks to be intact and hose clamps upstream are tight so it's not drawing air, you might try starting the engine and at <1000rpm closing the intake seacock for maybe 5 seconds then abruptly opening the seacock . Sometimes that can build enough suction for good draw and the sudden water pressure can knock a lot of gomph out through the system that can be seen as a brief black cloud in the exhaust water.

Has any work been done on the water pump recently that could possibly have allowed hoses to be reattached to the wrong sides of the pump, inlet vs outlet?
Not sure at all , but I'd ..think... even with Merc which had 1/2 FWC systems in the past, a FWC 6.2L MPI would be full FWC so the only hole in the ss blockoff plate between manifold and riser would be for exhaust. Any water passage holes in the gaskets shouldn't matter. . But it's a good question as to whether it definitely is full-FWC or just 1/2 FWC and that was never answered when asked above. Only that it is FWC with closed cooling system which could be either.
 
In board/thru transom exhaust?

Careful, without water running out your exhaust, you can burn up exhaust components.
 
Sandy hit on something, is the RW pump installed right? On merc's I know you can put them on up side down and they won't pump. If you're not getting any flow at all I'd bet on this.
 
quote:
Originally posted by talexander38

are you sure you used the right gaskets between the manifold and risers ?

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Thanks Tony, ( and everyone else ) you hit it right on the nose. I was given gaskets with no water holes in them. I have been busy with work and this weekend was the first chance to get back to the risers to trouble shoot.
With the 2001 6.2 mpi Mercruiser motors, do I need all four holes in the gasket or should I put in the restricter gaskets. Both are sold with the riser.

Thanks

Billy K.
 
quote:
Originally posted by littlebookworm

A little trick to help save your knuckles from getting scraped and your spark plugs from being broken. Pick up two bolts about an inch longer than you manifold bolts or some threaded rod the same size and an inch or so longer than the manifold bolts. They don't have to be stainless because you won't be leaving them in. If you bought bolts, cut the heads off with a hacksaw so that you've got two long studs. As you remove the outer manifold bolts, replace them with the studs. Then remove the inner bolts. Now you have something instead of your hands holding up each manifold. Slide the manifold off the studs and clean up the block surface. When it comes time to install the new manifolds, loosely screw the studs into the outer holes. Slide the gasket and manifold on. Install the inner bolts. Then remove the studs and replace them with the outer bolts. This way you wouldn't have dropped the manifold on your fingers or on your spark plugs. I did both of those until I learned this little trick. Also, before you install the manifolds or the risers, run a draw file lightly over each of the mating surfaces to make sure they are clean and flat or else you might have some leaks. Good luck. Hy

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WOW, awesome idea.That would make a near impossible one man job fairly easy.You get all the holes lined up and a set of "hands" to hold the unreal heavy manifolds.Not to mention not buggering the gaskets.

This should be a sticky type help topic for doing manifolds.
 
We need to know if the manifolds are fresh water cooled, if they are ,block off plates are used and the holes in the riser gasket don`t matter
 
Hi Guys,

The best I can tell is the raw water pump leaves to go through the transmission cooler, then fuel pumps and into the heat exchanger. The only way out of the heat exchanger has to be through the exhaust manifolds ( plus there are blue plugs at the bottom of the manifolds for fresh water rinsing ). The only hose on the risers goes to the dripless stuffing box. At this point I'm pretty sure I need holes in my gaskets. Do I need gaskets with four full holes or two full holes and two restricter holes.
Thanks for your patience.

Billy K
 
Billy;

You need all the holes in the gasket from the manifold to the riser open. Raw water doesn't hit the system until the very last moment.
 
It's sounding more like you have the 1/2 FWC cooled system, with coolant only in the block, not in the manifold, and no SS block-off plate between manifold & risers. If so, RW flows all the way through the manifolds ,gaskets & risers to the exhaust RW injection point by the end of the riser/elbow. No gasket holes, no RW flow. When you removed the old risers did you see any evidence of A/F coolant in the manifold passages you inspected or when you drained the manifold, or was it just RW? No original block-off plate, right?

Do you recall what the hole pattern the old gaskets had? Some mfgrs or exhaust systems use all 4 holes open for most total flow , others opt for just 2 gasket holes on side of the outside larger curve of the riser for greater RW pressure & cooling on the upper/hotter part of the riser. Recommendation for one or the other seemed to change back & forth, with 4 holes taking the edge I believe-not sure.
 
Thanks Guys,

I picked up the four hole gaskets and will get back to everyone after install. Thanks for all the help. Sandy, I don't remember but I'm pretty sure all the holes were open. I didn't think to look or even check the new ones because I didn't know there were three different types. I also was told it was a closed system which it isn't. It is available but I don't have it. Live and learn.

Thanks,

Billy K.
 
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