Exhaust Riser Information

Updated:4/23/09 Printer Version

Bob Cephas the owner of a 4100 SCA with Cummins 330B's had a "hot spot" in his boats exhaust tube. The hot spot caused the exhaust tube to fail bringing the engines HOT exhaust gasses and engines cooling water into the engine compartment.

Engine Cooling, Exhaust Risers, Possible 4100 SCA problem. We advise and inform the Maxum Family, of Maxum Owners, Maxum Dealers and Maxum / US Marine when we have received information from either impeccable or multiple sources that a potentially serious condition may exist on their boats. I believe this is the MOST important thing that we do. If what is discussed is unique to a single boat, so be it. The Fleet needs to be aware of and to pay particular attention to this item. If it is indicative of a problem common to the fleet we all need to know. The only way to do this is openly. To that end, our thanks to Robert Cephas, robertcephas@snip.net one of our 4100 SCA owners, I request our 4100 SCA owners, our Dealers and our service managers to contact him directly to fully understand what he has found regarding the exhaust tube failure in his 4100 SCA. robertcephas@snip.net (302) 368-1467---home

This information applies to all of us. The exhaust tube in Robert's 4100 SCA is rated for 250 degrees operations. There are many possible causes of the failure of the tube, one the tube was improperly made and/or improperly cured, (it is fiberglass). Possible, but not the most likely. Another is that the exhaust riser and exhaust configuration may be the culprit, this is more likely to hold the answer. An explanation here is required to get you up to speed. Engines are sold to Maxum without exhaust risers. The boat builder can choose to make them dry exhausts, like a car. Or wet exhausts by adding water to the exhaust gas. Maxum makes wet exhausts, and therefore must add an exhaust riser to the engine, in Roberts case on his Cummins Diesels just after the turbo. The Cummins Diesel produces test cell exhaust gasses temperatures of 898 degrees f for the 370B and 830 degrees f for the 450C, (source Cummins Marine SC.) The purpose of the riser is to spray engine cooling water through a "spray head" pattern of holes inside of the riser to cool the engines exhaust gasses. This spray pattern "ideally" blasts a perfect spray pattern of water hitting all of the exhaust gas, thus lowering the temperature of the exhaust gas under the 250 degree rating of the exhaust elbows and exhaust tube. Exhaust risers are a maintenance item, and they only last so long because of their extreme exposure to corrosive raw water and extreme temperatures. This riser is only a few years old and has under 200 hour of engine time. Therefore wear and deterioration should not be the cause. Cummins points out that in salt water, if your engines coolant flow is low and you raw water temperature exceeds 130 degrees you will get the salt in the water transfer to solids and build up on the riser spray head clogging it. Cummins points out that this is a maintenance item. The exhaust tube failures most likely cause is that the exhaust gas did not get completely cooled and there were voids in the spray pattern of the exhaust riser. The cause could be inadequate water flow through the engine to the exhaust riser due to anything from clogged engine water scoops to clogged sea strainers, blocked heat exchanger, to poor impellers, a broken piece of the impeller blocking flow inside of the engine, to kinked tubes and piping. It is suspected that the problem is exhaust risers spray pattern in combination with the swirl of the exhaust gas, in combination with the geometry of the inside of the tube and its elbows produces could have caused a void in the spray pattern. The cause of the failure could be a combination of many of these factors leading to an inadequate spray pattern. Changing the components after the riser to 350 degree components will only mask the problem, it should be cured. This is not to say the upgrading to 350 degree fiberglass exhaust tubes and 350 degree silicon elbows is a bad thing, it just would not have shown the base problem to the owners as quickly. 350 degree components will not harm the installation. The changing the exhaust tube from the original fiberglass exhaust tubes to metals is NOT an option. A metal exhaust pipe transfers heat too well and can exasperate an acceptable design, into a dangerous design with the use of metal. Robert is in the process of disassembling the risers and replacing them. Maxum is monitoring and supplying guidance to Robert in this. Additional information as it becomes available will be available through either Robert or on the website. It should be noted that running the engines with the engines raw water seacock's closed will send 800+ degree f exhaust gas into the 250 degree f rated exhaust system. The results, well you can imagine as well as I. If you’re a second owner, this is an area surveyors ALWAYS inspect thoroughly, just because it is a common point of failure. 2/2001

FYI, common exhaust materials are high quality 316L Stainless Steel., SMO, Inconel, Monel, Aluminum, Fiberglass / Composite Tubes. High Temperature Rubber, Silicone Hose is used as couplers, elbows and at times as exhaust tubes depending upon the application, 2/2001

Sources:

DeAngelo Marine Exhaust, Ft. Lauderdale, FL 800-952-8555 http://www.deangelomarine.com

National Marine Exhaust, Marysville, WA 360-659-2983 http://www.nationalmarineexhaust.com/

Marine Exhaust Elbows: I would have suspected that these were stock items. I just finished speaking to Delangelo Marine exhaust here in Florida, 3/2001, they do not stock Marine Exhaust elbows, they are all custom made to order. They do a "build to match" from your old unit and it takes about 2 weeks to get your new marine exhaust back. James

Robert W. Cephas
2801Ambler Court
Wilmington, DE 19808

April 04, 2001

Mr. Scott Conahan
National Marine Exhaust
14428 Smokey Pt Blvd
Marysville WA 98271-9916

Mr. Charlie Life
Maxum Marine Corporation
17817 59th Avenue NE
Arlington WA 98223

Mr. James Clausen
Maxum Owners Group
7067 Villa Estelle Drive
Orlando FL 32819

Dear Gentlemen

Your combined efforts that have culminated in solving a very serious problem with my 1998 4100 SCA 330 Cummins diesel port engine exhaust system is greatly appreciated.

The enclosed photos and sketches that show a before and after exhaust cooling water flow pattern, demonstrates a significant improvement in lowering exhaust temperature and equalizing the cooling effect through out the exhaust flow path as a result of the modified riser.

It is enlightening to know that in addition to owning one of the finest boats in its class, I also have a manufacture and support organization that stands behind the product as you have done.

Sincerely,

Robert W. Cephas