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I have completed my engine swap on my B31. Thanks to all who responded, Information was quite helpful.

Now I'm trying to decide how I want to plumb the exhaust and coolant ines on my replacement engine.
Original engine was raw water cooled all the way, never had an issue just flushed when I came back in.
Replacement has a heat ex-changer, I'm putting on new risers and exhaust manifolds, I can either run coolant in the exhaust manifolds and just raw out the riser or
run the raw through both the exhaust manifolds and out the riser.

I'm leaning towards running the raw through both the exhaust manifolds and out the riser. Concerned that the engine encased in that box that their could be heating problems.

Just wondering what other boaters experience has been and recommendations before I hook everything up.

Thanks

The two different sets of engines I've had on my B28 are FWC. Both used kits to FWC manifolds with block-off plates between manifolds and risers. Risers are raw water cooled. Expect to get ~3 years (maybe 4) of use out of risers. May get more years out of them depending on how often you use the boat and dilligence in flushing. If you use raw water in the exhaust manifolds, I would expect that they would not last long either, but I don't have direct expience in that. If they are FWC, then the exhaust manifolds should last as long as the base engine. Expense of replacing my risers is ~$160 each x 4 = $640 every ~3 years and only takes about 1 hour per engine. Expense of replacing exhuast manifolds is ~$200 each x 4 = $800 every ???? years.

I have no issue with heat. They work as advertised. I check both risers and manifolds (and everything else) with IR temp gun a couple of times a year. When risers get above 104 deg F at idle and engine temp runs ~10 deg warmer on cruise, I know it's time to replace risers. Another good check is to take temp of exhaust hose right behind risers. Temp should be about equal all around the hose. If the hose has severe hot spots (like >50 deg temp changes) then you know your getting some clogging in your risers.

My $0.02 - FWC the exhaust manifolds.

PaulJ
1973 B28 - PALADIN

Much Thanks

Keep as much fresh water in that engine as you can. They don't get hot enough to worry about that.

While I would have preferred to have Manifolds FWC...I bought boat with them raw water cooled. Original owner had at least 6 years on them and I put about 8 more on them before I decided to "Just change them". They looked fine with lots of meat left.

Risers on the other hand have smaller intricate passages that corrode and clog up quickly and need to be replaced pretty often. An option I went with is a Copper Riser setup...they just last and last...pinholes that do occur can be brazed and back in service again for years...much better flow too. That is unless you are in a rush, do not braze well and destroy it trying to fix...cough cough.

Side Story-
One of the old timers here had a Chris Craft named the Enchantress. She had Chris Craft engines with Copper manifolds/risers. They were leaking terribly... A good friend worked for Gorham Silver at the time. The manifolds/risers were smuggled in to the Gorham Design/Private Client shop for major surgery. Three German fellas went to work on them. The boss just happened to be walking through on a Friday afternoon (never happened I'm told) and was interested in checking up on a piece that had been commissioned...He was appalled at what he was looking at until he realized that it wasn't a Gorham piece.
They got back to work on stuff like this:

FWC the manifolds!!!! My 440 Chryslers have the same log type manifolds that came on them back in the 80's as well as the Bertram copper double walled Y.

Hey Rawleigh, You knocking on wood??

Thanks to all I am convinced that FWC the manifolds is the way to go.

One more plumbing issue, the boat I believe has the original Y where the two exhaust lines come together. It looks really rusty and corroded from the outside but seems solid all the way around.

Since that Y sits below the water line it just looks a little risky, or am I just paranoid? Is there an fiberglass replacement part for that piece of pipe?

Thanks

gcreas1 wrote:Is there an fiberglass replacement part for that piece of pipe?

http://centekindustries.com/fittings.html

Thank you!

Mikey wrote:Hey Rawleigh, You knocking on wood??

Yep!!!!

Here is my theory. My previous boat had FWC manifolds and raw water cooled risers, and my 31 Bahia Mar has raw water cooled manifolds and risers, but the engines are FWC. I prefer the raw water cooled manifolds over fresh water cooled manifolds. When the manifolds are FWC, there is a blocking plate gasket between manifolds and risers. That blocking plate gasket is under pressure on the manifold side, and probably always has raw water resting at the bottom of the riser sitting on top of the gasket which will increase the possibility of rust and corrosion on the bottom of the riser. By having both raw water cooled, the water flows right from the manifold through the riser which does not put pressure on the gasket and won't allow water to sit in the riser water jacket near the machined mounting surface. My engines are 1995s, and I changed the manifolds about 4 years ago but have no idea if the previous manifolds were original or not. I believe my risers are original, but they are Mercruiser cast stainless and they are like bran new. I installed those on my previous boat back in the early to mid 90s, and inspected them and changed the gaskets before I sold it in 2001, and the stainless risers were like new then. Mercury doesn't make them any more, but if you look hard enough, they can be found in the used market. I have seen them on more than one occasion at the marine flea market for about $80 each. I was told that the reason they stopped making them is because they heat and cool down differently than the regular cast manifolds which causes leaks on the blocking plate gasket. I raise the B.S. flag on that because with fresh water cooled manifolds, they will be much hotter than the risers anyway which along with the cooling system pressure will be likely to cause gasket failures and leakage. With the raw water cooled manifolds, the temperatures of the manifolds and risers are much closer where they are joined together and the water flows from the manifolds through the risers with no trapped water sitting on top of the blocking gasket as with FWC manifolds. That is just my opinion based on my 20 years of experience owning both type of cooling systems.

Thanks much, your experience echoes my concern about the difference in operating temperature. Since the engine was already plumbed for FWC manifolds I have decided to at least set it up initially that way and run it for a while to see how it performs. Easy enough to convert it back to raw water if I don't line the performance.