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Mercruiser 5.7 exhaust Manifold options

O

outobie

Regular Contributor
I'm planning to replace my exhaust manifolds when I pull my boat for the winter and am looking for recommendations on type and brand.

I have a new to me 27' Tiara with twin 2001 5.7 alpha 1 gen 2 drives

The exhaust manifolds are the original raw water cooled wet joint cast iron mercruiser ones that came with the motors 16 years ago. Motors had 450 hours on them when I bought the boat in April. I've put just about 90 hours so far this season and will probably do another 20 before I pull the boat for the winter.

Boat is kept wetslipped on the Magothy river north of the Chesapeake bay bridge in fresh...ish water. At least not salty like the ocean. (I'd love if someone could tell me what to call the water I live on)

Anyhow here's my questions.
Should I stick with OEM manifolds?
Should I replace risers?
Should I replace elbows?
Anything else? How about the "Y" in the back?

what do people think about going with aluminum manifolds? Besides being lighter what are the other pros or cons?

If I stick with OEM should I consider changing to the dry joint system? If so what other parts need to be changed for the conversion?

Any brands people recommend or suggest I avoid?
Amy tips and tricks you can suggest to someone doing this for the first time?

Thanks
John
 
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Your boat lives on "brackish" waters....

I would stick with OEM manifolds, etc.
If you in fact have separate risers and elbows, I'd replace them both.
As long as you have it apart I'd at least inspect the "Y". While a failure of the "Y" won't be as catastrophic to the engine as an manifold, riser or elbow failure for example, it could result in a sunken boat. Furthermore, you can't "find" either the labor or parts cost in this project's cost.
Weight savings IMHO not worth the money... and... aluminum reacts badly to hot salt water.

I have a center rise dry joint system on my engine. It works as advertised and well worth the money. I ran across a technical paper about exhaust elbow design and its impact on "exhaust reversion", i.e. sea water getting back into the cylinders while running. Recent production OEM Merc elbows do not have this problem... anyone else's elbows is a big ????????.

Tips.... heat, i.e. a torch may be your best friend...
"chase" all threaded holes with a tap and make sure they are clean.
Use a torque wrench.
Follow mfg's instructions to the "t".
Make sure you have the correct gaskets between the manifolds and any down stream parts for your application.
Use all new OEM bolts for the manifolds and elbows.
Cut the heads off of two of the old bolts and insert them loosely into the block as alignment pins to make sure gaskets stay aligned as well as an aid in aligning the manifold. Then use these same two cut off bolts to align the gaskets and elbows.
Make sure there is no crap on the old surfaces before reassembly.
Replace cooling water hoses while you are at it.
Further... chasing tapped holes....MERC seems to have gotten cost conscious to a ridiculous degree and does not protect the hole that you will need to plug with the provided brass plugs or thread hose nipples into, with tape before painting. As a result, you will need the clean out the threads in the holes on the elbows ( and likely the manifolds) with a tap before inserting plugs or plumbing fittings in order to get a good seat. Its a big tap (sorry forgot size) and not always easy to find at your local H/W store and almost never a part of an inexpensive tap set.
Aviation Form-a-gasket.... the dark brown goop in a plastic bottle is a good sealer to use instead of the MERC recommended stuff.
 
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If you're chasing threads in the mani, you'll need NPT pipe taps. I think the one you want is 1/2".
Do not buy aluminum manifolds, the Bay water will react with the metal and form hard white "fluff" inside the water passages. This will eventually clog up the passages and the engines will overheat and die.
Original is best, even tho quite a bit more expensive than aftermarket.

When you put the boat up for the winter, be sure to drain the engines of all water. DO NOT fill with antifreeze.
Do an oil change. relieve belt tension, take batteries ashore. In spring, tighten belts, new water pump impellers, new fuel filters, tune up parts, and fresh gas.
 
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Thanks for the tips
sounds like going back stock is the way to go
a few follow on questions...

both outdrives were fully serviced July 4th week. (Water pumps, bellows, oil and gaskets).
i wouldn't expect to need another new impeller just yet should I? I was thinking the new one would be replaced again in fall 2018.

whats the current thinking on fuel for the winter?
pre ethanol I was told it's best to keep the fuel tanks filled for the winter .

more recently I've heard that with ethanol fuel it's best to drain the tanks for the winter

thoughtz on which is best?
 
Oh boy! That's a subject that has been heavily debated, and the answer is: Both. If you leave the tanks full, less moisture will be drawn in (do to temp cycles). If you thoroughly drain the tanks, both now and BEFORE refueling (to get the moisture out), the gas will obviously be fresh. The problem with draining them is that most marinas won't allow it for safety reasons--a tank full of fumes is a massive bomb. (If you trailer home, then that's not a problem.)

I've put up with Evil-Nol fuel for a decade now and, to be honest, I've never had a problem. That said, I use Startron additive every lay up (tanks roughly half full) and I run my outboards dry after every run. It's your choice.

Jeff
 
outobie said:
whats the current thinking on fuel for the winter?
pre ethanol I was told it's best to keep the fuel tanks filled for the winter .

more recently I've heard that with ethanol fuel it's best to drain the tanks for the winter

thoughtz on which is best?
Click to expand...

Top off the tank and use the appropriate amount of fuel Stabilizer. I prefer to use Stabil 360: https://www.goldeagle.com/product/sta-bil-360-marine
I use that on every fill up and for winterizing. It helps to disperse any moisture in the fuel and keep you from sucking up globs of water.

KJ
 
I've been adding Startron with every fill up and sea foam to every 3rd fill up.

Sounds like leave it full is the way to go. Maybe I can find real gas to leave over winter
 
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