Mercruiser Warm Riser vs Cold Riser Configuration?

[Greg_E]

2003 Mercruiser 6.2L MPI Horizon MIE. I will be replacing the manifolds, 3" risers, and elbows over the winter.
The engine is currently in the cold riser configuration. The obvious benefit of going with the warm riser is the risers should last much longer with coolant running through them vs salt water.
It is a mystery to me why the cold riser configuration would be used when all that is required is moving a couple fittings and gaskets around and changing a couple hoses that may be a little short after the change but that is how I found it.
I was just wondering if there is some reason or situation where the warm riser configuration should not be used?

 

[alldodge]

Reading the title I first thought this was an old motor and wanting to go to warm mans, but your wanting to go to closed cooling or full closed cooling.

Does your motor have a heat exchanger (HE) now?

 

[Greg_E]

The engine is already full closed cooled with dry joint manifold, 3" spacer, and riser. When those items were installed, the person that did it put the block off gasket between the manifold and 3" spacer. so coolant flows only through the manifold, and the spacer and elbow are cooled with raw water. By putting the block off gasket between the spacer and elbow. and repositioning the hoses so coolant flows through the spacer and manifold. and feeding the raw water just to the elbow, the spacer should last much longer. The manual shows both configurations, but does not state if or when one configuration should be used. The warm riser seem to be a better way to go. I'm sure Mercury Marine doesn't see it that way. They will sell a lot more spacers with the cold riser setup.

 

[alldodge]

Ok, thanks, so many folks mix terms so I wanted to make sure.

Manual 37 list closed cooling to be done the way it is now. Manual does use the terms cold and warm risers to understand if its raw water or antifreeze cooled.

The manual doesn't state the actual why, but if the riser was coolant filled then for the most part very little coolant would be exchanged. Also the riser could get an air pocket form and there is no way for the air to escape, so it would need to be bleed off when coolant was added.

 

[Greg_E]

My Dry Joint Exhaust Manual is down on the boat but the way I think it worked, was this. The block off gasket is placed between the elbow and spacer. The full flow gasket is placed between the spacer and manifold. The plug in the elbow is replaced with a hose barb and the raw water hose is connected to the elbow. The hose barb that goes to the top of the manifold is removed and plugged and that hose barb is placed in the spacer. The spacer is installed with the hose barb at the top of the spacer so that the coolant flows though it on its way to the manifold.
I'll check the manual next time down. I think one of the benefits was that any condensate that dripped down the inner wall would be caught on the upturned lip of the gasket and the spacer, warmed by the coolant, would help evaporate that water as the engine cooled. The diagram you posted would be the cold riser and what I just described is what was referred to as the warm riser.

 

[alldodge]

The diagram you posted would be the cold riser

Yes its the cold one, for closed cool
The warm one is used for open cool

 

[Greg_E]

I was able to find Manual 37 online and have attached the assembly drawing and flow diagram for closed cooling with warm riser configuration. Hopefully this clears up what I'm trying to do.
One correction to my post #5 is that the coolant flow enters the bottom of the manifold and out of the top of the riser.
This configuration can only be used if your engine has risers (spacers) between the manifold and elbow. Older versions of the riser could only be used for cold riser. I think all the newer risers from Mercruiser or Barr can be used in the cold or warm configuration, but don't quote me on that. If there is a notch for the water to drain from the bolt holes top and bottom the spacer can be used for cold or warm riser.
Back to my original question, Why wouldn't you use the closed cooling, warm riser configuration and greatly extend the service life of the risers? I don't see any advantage to using the closed cooling, cold riser configuration.

 

[alldodge]

Why wouldn't you use the closed cooling, warm riser configuration and greatly extend the service life of the risers? I don't see any advantage to using the closed cooling, cold riser configuration.

Got it
I see your point and only thing is the risers will place more heat in the engine room, other then that I would agree.

But manual shows layout for the inboard but not the I/O. Don't have the answer, and maybe someone else might. or maybe ask the question to Merc

 

[Greg_E]

I have twin inline inboard engines so I'm all set. The flow diagram I uploaded says it's for "Close Cooled Bravo and Inline Inboard Engines With Warm Risers" Isn't the Bravo I/O? I always had outboards so I'm not up on that stuff and still have a lot to learn about the inboards.There even was another diagram for inboards with V drives for those that have them.

AD Thank you again. You have helped me numerous times since I bought this boat about a year and a half ago.

While I'm at it I need to make a correction to my post #3. The first sentence should read "The engine is already full closed cooled with dry joint manifold, 3" riser, and elbow. I have seen the term riser and elbow used interchangeably, especially when no riser (spacer) is used and I guess it stuck. If we all just use the terms manifold, riser (spacer), and elbow. it would make it less confusing to the people here that help us.

 

[alldodge]

"Close Cooled Bravo and Inline Inboard Engines With Warm Risers" Isn't the Bravo I/O?

Your right