Pulled risers to check, glad I did

SCORPIO

SCORPIO

Well-Known Member
Apr 7, 2008
2,742
Delaware
Boat Info
1989 300 DA
Engines
Twin 5.7 Merc Alpha I
I pulled the risers off my boat last night. These engines are both new crate motors. The port was replaced spring 2015 and the starboard in August of 2016. They both have closed cooling half systems, meaning the risers and manifolds see salt water. The port engine has Mercruiser manifolds and risers and the starboard has Barr units. I found quite a bit of surface rust in three of the exhaust manifolds! No valve damage and no bore damage confirmed using a bore scope in all the spark plug holes and exhaust ports. Looks like the riser gaskets must have leaked and let some water into the exhaust manifolds. The gaskets all looked intact and the water passages all appeared to be in decent shape, only surface corrosion, no scale or clogging or flaking rust. If I had run those another season without inspecting, I could have lost one or both engines. Since I cannot confirm the riser gasket seeping, I ordered all new Mercruiser manifolds and risers for both engines. The piece of mind is worth the cost. I'll scrap the old units and move on. My plan going forward is to pull the risers EVERY YEAR and inspect and replace gaskets. I thought I was well withing spec pulling after two and three years respectively but that doesn't seem to be the case. BTW I did retorque the risers and manifolds after the first hour and then again at ten hours so that wasn't an issue.
 
I’m going through a similar situation here.
I found a crack in the port side exhaust manifold which dripped water externally when running.

Pulled the risers and manifolds, manifolds were blocked with debris and I found rust stains inside the starboard manifold right below the riser. Also had rust stains around the elevated lip of the starboard side riser gasket (dry joint manifolds). No evidence that the water made its way into the cylinders.

I can’t see where the riser is leaking, but small amounts of water are obviously getting into the exhaust manifold.

New parts on order and I should be back on the water in a few days.

11 seasons and 300 hours.
 
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Have you looked into converting the system to full? Only getting 2-3 years out of your manifolds will cover that upgrade in a hurry.
 
I think it was a riser issue not manifolds but I'm going to start with a clean slate. I was told my Alpha 1. Pumps won't supply a full system and I'll have overheating issues if I went that route. I wanted a full system when I went with the new engines.
 
You can run a full system using the Bravo style engine mounted pump and just cut the hose for the Alpha . It still needs a impeller to cool the drive
 
SCORPIO said:
I think it was a riser issue not manifolds but I'm going to start with a clean slate. I was told my Alpha 1. Pumps won't supply a full system and I'll have overheating issues if I went that route. I wanted a full system when I went with the new engines.
Click to expand...
I was faced with the same situation when I repowered my old 87 300 Sundancer and like you, I went with the half systems. It was just too tight on the front of those motors for a raw water pump. Swapping out the impellers would,have been tough.
 
Other than extending manifold life, a leaky riser gasket would still put water into the manifold even with a full system as would a failed riser. I don't think there were any casting issues but looking down into the manifolds and seeing rust and signs of water, I couldn't feel comfortable reusing those units so I went new just for peace of mind. I will pull the risers each year from now on and inspect and replace the gaskets to hopefully prevent any future damage.
 
I got mine buttoned up yesterday.
Here’s the starboard side riser gasket with the rust stain around the lip. The port side gasket only had carbon, no rust stains.
EF0F3560-38E9-40B2-9099-80CD96E6220B.jpeg



Here’s the rust stain inside the manifold from the same side as the gasket shown above

32405A27-ABA2-4D1A-B928-8273FFAE35F5.jpeg

8DDA9A1E-EFAA-4A7A-B055-551C07059860.jpeg

I pulled the plugs and checked the cylinders. No evidence of water getting inside.

Using the threaded rods with the heads cut off is a life saver. I also cut a slot on the end of the rod for a flathead screw driver.
 
Bt Doctur said:
You can run a full system using the Bravo style engine mounted pump and just cut the hose for the Alpha . It still needs a impeller to cool the drive
Click to expand...
Which hose are you referring to? Isn't the one in the outdrive above waterline while on step. My tub came with a thru hull t'd into hose from the pre alpha near the inlet of the engine mounted pump. There is a ball valve at the thru hull for running on the muffs.
 
Espos4 said:
I got mine buttoned up yesterday.
Here’s the starboard side riser gasket with the rust stain around the lip. The port side gasket only had carbon, no rust stains.
View attachment 55854



Here’s the rust stain inside the manifold from the same side as the gasket shown above

View attachment 55855

View attachment 55856

I pulled the plugs and checked the cylinders. No evidence of water getting inside.

Using the threaded rods with the heads cut off is a life saver. I also cut a slot on the end of the rod for a flathead screw driver.
Click to expand...
What you have in the manifold looks like what I found inside mine.
I cut slots in my rods too, and you are right about them being a life saver, don't know how I'd install the outboard manifolds without them.
 
They way the dry joint should work is no water mixing with exhaus until it exits the riser elbow into the exhaust hose. The rust on the tubilator lip should only be condensation dripping down the inside riser and pooling around the tubilator lip hence the rust. In otherwords, its doing its job
It appears you my have had excessive condensation where water went over the lip.

Once the engine fires up any condensation left is burned off in a matter of seconds.

Why I start my engines and run 15 min weekly during the winter and early Spring.
 
Thornton69 said:
Which hose are you referring to? Isn't the one in the outdrive above waterline while on step. My tub came with a thru hull t'd into hose from the pre alpha near the inlet of the engine mounted pump. There is a ball valve at the thru hull for running on the muffs.
Click to expand...
The hose from the gimbal to the transom. Most cap it inside the boat when they convert but the drive uses that water flow to cool the oil in the drive .
A full system needs a thru hull and engine mounted pump. The impeller in the drive is now only used to cool the drive. Some have removed the impeller entirely and depend only on flow from the inlet holes while under way but thats not the brightest solution either.
 
the turbulater lips should face upwards to trap the moisture
"I found quite a bit of surface rust in three of the exhaust manifolds! No valve damage and no bore damage
Looks like the riser gaskets must have leaked and let some water into the exhaust manifolds. "

there is no water jacket on the dry joint manifolds , water goes thru the 2 ports and uses a rubber ring seal. Are you sure the rust is not reversion?
 
Bt Doctur said:
the turbulater lips should face upwards to trap the moisture
"I found quite a bit of surface rust in three of the exhaust manifolds! No valve damage and no bore damage
Looks like the riser gaskets must have leaked and let some water into the exhaust manifolds. "

there is no water jacket on the dry joint manifolds , water goes thru the 2 ports and uses a rubber ring seal. Are you sure the rust is not reversion?
Click to expand...

I think you have melded 2 different responses into one.
Scorpio, the original poster, had water in 3 of the manifolds. Judging by his info, I'd assume he has non dry joint manifolds.

I had the rust stains on the turbulator lip on starboard side only. I understand the lip is there to catch and trap condensation, but my port side gasket had no such rust stains. I also had rust stains from water pooling inside the exhaust manifold starboard side only.

My model boat doesn't have a "bad" history of water reversion problems, the exhaust flappers are in perfect condition, I always come off plane in a manner as to prevent reversion, so I am not concerned about this being caused by water reversion.

That, coupled with the 11 years being wet slipped in salt water, made it an easy decision to replace the manifolds and risers.
 
I do not have dry joint exhaust. Some of what I saw in the manifolds could have been condensation caused but one of them had a tiny pool of pink antifreeze so that would be consitient with seepage at the gasket as anti freeze was the last thing put thru the manifolds prior to winter.
 
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