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2004 Crusader 8.1 Heated Riser

R

readyforescape

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My 2004 Crusader 8.1L has two exhaust options: heated and unheated 4" riser (spacer). One option passes sea water through the 4" riser up to the exhaust elbow and out with the exhaust. The other option passes sea water directly to the exhaust elbow and out with the exhaust. I can plumb for either option. Why are there two options? Is one better than the other? It would seem that not passing sea water through the 4" riser would reduce corrosion potential. Thank you for your response.
 
I don't know that there is a definitive answer. Pascoe suggests that the 'warm' configuration will ensure the riser lasts a long time, compared to the elbow.
Two options - straight forward answer is cost...some people are really cheap...
FWIW, the main risk tied to corrosion is at the elbow...and the best mitigator is replacement...depending on where and how the boat is used figure 4-7 years...
 
FWIW, i checked my mercruiser manuals...for all of their center riser configurations, they want the riser cooled with raw water. they provide a note stating that plumbing the riser is a 'warm' configuration could lead to a steam pocket forming inside of the riser...
 
Thank you for the additional information. My 2004 8.1L Crusader manual shows both configs without discussion of application. Does the Mercrusier manual confirm or conflict with Pascoe?
 
i would say they do not conflict.
I'd say mercruiser's concern is for an air pocket forming in the riser with the 'warm' configuration. Looking at the risers shown in the manual, it makes sense at the water fitting is in the middle (of the veritcal extent) of the riser...
 
Crusader's claim to fame is the ability to use "fresh water" to cool much of the the elbows (and risers) . If you engine does not have a heat exchanger and is therefore "raw water cooled", you may as well run sea water thru the riser. If it has a heat exchanger and is therefore "freshwater cooled" , include the riser in the engine's jacket "freshwater loop" and inject ( or dump) the sea water out directly into the exhaust elbow.
 
Thank you for your response. This seems to be the majority opinion including Crusader Engine technical direction. Crusader offers both options and states that non-salt water applications can use freshwater for the riser and elbow but salt water applications should run freshwater only to the elbow. Crusader also offers a non-riser option.
 
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