Question about 1999 Mercuriser 350 FWC system:

[Defender]

What part of this system uses fresh water for cooling and what part uses raw water. Specifically are the manifolds cooled using fresh and the risers / elbows with raw?

My last 454 Mercuriser was raw water cooled and understood that system.

Thanks

 

[mwph]

Im suprised at the lack of replys to your question. There are a thousand more qualified guys on this board to answer than I but.... I thought that with a FWC system, the engine is cooled by the fresh water/coolant, and the water/coolant is then cooled using raw water.

 

[Defender]

Thanks, I was suprised as well. There are usually lots of feedback on these questions.

Well back to the question, I thought there were two types of these FWC systems, short loop which just the engine block is cooled using Fresh water and long loop which the engine and exhaust manifold only is cooled with fresh water. With both systems the exhaust risers and elbows are still cooled using raw water. I tried to look and follow the hoses to see but, well there are alot to the system.

Thanks again

 

[Westie]

I'm not familiar with the exact system that you have but I just installed a full fresh water cooling system on my boat so I might be able to give you some help.

First of all how many hoses go to each manifold?
Mine had one hose to each manifold before the installation, two after.
How warm do your manifolds get? On a full system the manifolds will run warmer because they are cooled from the fresh water side which will always be warmer than the raw water side.

 

[Tail Chaser 661]

There is 1/2 system and a full system
You could do a search and check out the hose routing.
I'm thinking 1/2 fwc runs raw water through the exhaust manifolds. Full fwc runs engine coolant through the exhaust manifolds. I have never completely researched how the hoses are routed though.
Something else to add on my things to do list.

 

[Defender]

Thanks, well after looking at the cooling hoses I found each manifold has 2 hoses, 1 at the bottom and another at the mid point of the 3" riser block. Then there is another that goes into the top of the riser elbow as well. definitley more going on here than my last boat. I remember having only 1 hose going to the bottom of each manifold and that engine was raw water cooled.

Thanks

 

[fc3]

Thanks, well after looking at the cooling hoses I found each manifold has 2 hoses, 1 at the bottom and another at the mid point of the 3" riser block. Then there is another that goes into the top of the riser elbow as well. definitley more going on here than my last boat. I remember having only 1 hose going to the bottom of each manifold and that engine was raw water cooled.

Thanks

That makes sense. The lowest hose is coolant entering the manifold. The hose on the riser is coolant going from the exhaust system to the heat exchanger. The hose on the elbow is raw water out to the exhaust. Only the elbow is raw water cooled on your engines.

Best regards,
Frank

 

[Nehalennia]

Here is a great site illustrating both 1/2 and full systems.
http://www.orcamarine.com/faq_and_tips.html#what2

 

[Defender]

Wow great info, thank you all.

Nehalennia that link had some great information. I'll be looking into some of the inspections mentioned in that link this week.