I also like to know that.

 

On my boat, (6.2 horizons) the manifolds had antifreeze running through them. The risers had raw water. There is a gasket between the 2 that keep the systems separate. When my risers failed I was told by a mercruiser dealer that I needed to replace the manifolds as well and ordered everything. Only after placing the order did I realize that he was wrong. I did not need to replace the manifolds. He wanted 20% restocking fee plus shipping to ship them back to Mercruiser. I ended up buying them and selling on ebay. Still took a few $hundred dollar loss because of his mistake :smt013. Anyway.. if you are raw water cooled replacing the manifolds with the risers is standard procedure, but not with fresh water/closed cooling. I am sure the next thing to go will be the heat exchanger that is exposed to salt water. I would wait for a few other responses before taking what I say as accurate, but this is my understanding.

 

Call mercs customer sevice # with your engine ser. #. They will tell you. You could loosen a couple of hoses going to the manifolds and risers and figure it out yourself. The elbow to riser gasket would also tell the story, you can look that up on mercs website.

 

Generally, only the block is in antifreeze. The rest is raw water. The only other area would be the manifolds. Some newer systems have antifreeze cooling the manifolds and raw exiting the riser. Ie. Dry joint non raw water manifold. Most engines run at 160 degrees with raw water manifolds. Add 10 to 15 degrees if no raw water and antifreeze only. At that point that's a true closed system. Most though are 50/50, open closed.

 

You should contact Sea Ray or whoever installed your system there are 2 types of FWC systems Full & 1/2 systems, here is an explanation our boat has a full FWC system.

https://www.perfprotech.com/blog/articles/fresh-water-cooling#

Topic: Fresh Water Cooling – What are the differences between Fresh Water Cooling Systems and Raw Water Cooling Systems, and what is the Difference Between a Full & Half System?

Half Systems vs. Full Systems:
The 1/2 systems circulate glycol thru the engine block only, where as full systems circulate glycol thru the engine and exhaust manifolds. Generally speaking the advantage in a half system versus a full system is with performance applications. The reason for this being that performance engines generally reject more heat load to the heat exchanger and therefore the system functions better without the additional load of the exhaust. The other item to consider is that even with Fresh Water Cooling most boaters still choose to flush their system and drive unit and therefore the corrosion protection issues really aren’t as relevant between the two systems as most consumers suspect. If you operate in corrosive water conditions and choose not to flush at all, your risers and sterndrive will experience corrosion even with the full system. Half systems do allow for easier installation as well as allowing for an overall more efficient system, while still protecting the main investment (the engine). The real issue to consider with a full system is the advantage of running warm exhaust manifolds. The newer engines being produced today are built with engine management systems that stabilize the idle rpm of the engine. This is done by varying the ignition timing of the engine. The problem with this involves the issue that having these ignition timing spikes tends to allow certain engine configurations to be more prevalent at drawing water back up through the exhaust system. This problem in combination with the condensation created by running “cold” exhaust manifolds sets up a situation that the full system is very good at preventing, this because the exhaust manifolds run at a temperature high enough to evaporate any collected moisture.

 

Follow the hoses from the manifold back to source. You will then see if it is raw or anti freeze as noted above best way is to just loosen one clamp.
Our manifolds are cooled by anti freeze and the only salt water is in the riser.

 

I'll give this a stab as I've worked on enough of them but I am not an expert.

Most marine engine exhaust manifolds will work for both closed (fresh water cooled) and open (raw water cooling) engine cooling. There are plugs at different places to allow water in or out of the manifold. The 2 other main components are the raw water pump and the heat exchanger. With a fully closed system, engine coolant is pumped through the engine with the recirculating pump on the front of the motor and that also includes the exhaust manifolds. Raw water is introduced through the raw, or sea, water pump, through the heat exchanger and out with the exhaust.

There are variations.... I've seen raw water also cool the manifolds but I can't see the advantage of that.

Anyway that's what I know and I'm sure others with jump in.

Shawn

 

Eblows and risers are 2 different things. So you have manifolds, risers (on some engines, depends on water line) and elbows. On my boat which was equipped with FWC from Searay, my black, manifolds and risers are FWC with the risers, fuel cooler, p/s cooler and of course heat exchanger being raw water cooled.

 

The easy way to tell if you have a half system or a full system is look at the hoses to the manifolds and elbows.

On a half system there will be one hose to the bottom of each manifold. This is raw water and it goes through the manifold up the riser (if you have one) then into the elbow and out the exhaust.

On a full system there will be 3 hoses per side. One at the bottom of the manifold, one at the top of the manifold (or possibly from the riser, again if you have a riser). The bottom hose is coolant to the manifold and the top one is coolant return.
A third hose carrying raw water will go to the elbow.

 

Thanks for the replies guys. I did speak to Merc and they confirmed that my engines are "1/2 Loop" closed cooled, meaning just the block. Manifolds and risers are sea water.