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- Cummins Marine Forum Topics
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Intermittent not reaching high cruise RPM
This topic has 2 replies, has 2 voices, and was last updated by
4 months ago
July 13, 2023 at 9:14 pm Something odd happens today. CAT 3126 MUI normal cruise about 2400 rpm max is 2850. Trolling speed for about 6 hours then time to run for home. STBD engine was at the throttle stop and only reached 2350. Ran fine at that RPM. So I throttled down ran it up and went right up to 2850 throttled back to cruise RPM 2400 and slowly had to keep pushing the STBD throttle forward until it was at the stop again holding only 2350. Port throttle was in its n…
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in: All Other Marine Diesels
2 RepliesDecember 31, 2023 at 2:16 pm No one yet? Did you get it sorted out?Last Post by:
posted: 4 months ago
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Fuel burn says Iām over loading the motors..
This topic has 15 replies, has 6 voices, and was last updated by
7 months ago
February 28, 2021 at 8:41 am CAT 3126 420 HP 2800 WOT. Purchased new 3 blade ACME props 2 seasons ago and it made a big performance difference and the boat is running great. But… hereās the rest of the story. Finally got fuel flow info. RPM CAT spec. GPH My burn 2850. 23.0 23.1 2500. 15.0 15.5 2400. 13.2. …
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in: General Discussion
15 RepliesSeptember 21, 2023 at 6:18 am The standard power requirement curve says that the power (and fuel burn) needed is directly related to the RPM raised to some exponential factor. Cummins uses 2.7 for the exponential factor. I analyzed the Cat specs in your first post, and it is clear in that case the exponential factor is 3.0. So, yes, the factory specs are different. The Cat spec is a bit more restrictive at mid-range RPMs. However, that is irrelevant for either Cummins or Cat…Last Post by:
posted: 7 months ago
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Impeller quality vs price
This topic has 3 replies, has 4 voices, and was last updated by
1 year ago
April 3, 2023 at 6:24 am I see the Sherwood 17000 series for sale on line from around $35 to $70 a piece I ended up buying a 2 pack from sherwood $105 thinking the cheaper ones are probably inferior. Anyone know for sure?
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in: General Discussion
3 RepliesApril 3, 2023 at 5:14 pm Ya don’t say, LoL. This one had me looking at the entire HX system before getting to it since it was relatively new I didn’t even think about it. But once I tried to remove it and saw just the hub coming out….I knew it was the issue.Last Post by:
posted: 1 year ago
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Prop speed, worth doing?
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This topic has 28 replies, has 16 voices, and was last updated by
2 years ago March 1, 2019 at 12:30 pm Thinking of trying some new ACME props and wondering while Iām at it if I should put prop speed on the running gear. Has anyone had experience with this product?
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in: General Discussion
March 7, 2022 at 1:22 pm I’ve had good results with prop-speed.Ā Basically extended cleaning the running gear for 12 months and not having to pull the boat last season.Ā Ā Prop-speed applied May, 2020 No running gear cleaned in 2020 1st cleaning Labor day weekend 2021 (had lost 2 knots), one side was fine the other had a barnacle strikeĀ Had diver clean running gear again in Nov B4 the water got to cold as a pre-cautionĀ Once its scape it’s lost it’s ef…
28 Replies
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posted: 2 years ago
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Exhaust pipe min diameter for 420 HP
This topic has 7 replies, has 2 voices, and was last updated by
2 years ago June 10, 2021 at 2:27 pm Had new exhaust riser built. Sent them old one. New one came back with 3 inch pipe from flange to bolt on turbo. Old one was 3 1/2 inches, they want me to do a back pressure test to see if itās ok as is. I looked at a chart that says 3 inch too small for 420 hp. I want a new part. What do you guys think?
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in: General Discussion
7 RepliesJune 11, 2021 at 10:32 am Spoke with the owner today. He said they will fix it. So Iām gonna hope for the best and see what happens next. Hard to understand how this got missed but it did.Last Post by:
posted: 2 years ago
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Over Propped
This topic has 12 replies, has 7 voices, and was last updated by
3 years ago December 21, 2020 at 7:58 am I have twin 6bta’s Cummins Diesel 370HP about 700 hours on each. My current max rpm is 2850 and I have read on this forum that the ideal rpm should be 3150 at WOT. What would be the benefit of getting my props properly pitched?
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in: General Discussion
12 RepliesMarch 30, 2021 at 3:29 am Harry, yes a percentage delta vs. a fixed delta can be expected. Easy enough to verify at the dock with a fully warmed up engine.Last Post by:
posted: 3 years ago
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Qsb-380 Coolant loss
This topic has 8 replies, has 6 voices, and was last updated by
3 years ago January 2, 2019 at 3:40 am I am on my second full year of ownership of a 390 sundancer. I’ve noticed a small loss of coolant on the expansion bottle with no visible leaks, oil clean without any moisture. I remember reading that it could be a problem with the turbo gaskets or cracks. I am ordering parts for my after coolers now and would like to address this issue now. The after coolers were never serviced, one a total loss, one rebuildable
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in: Cummins Marine Engines
8 RepliesNovember 20, 2020 at 5:53 am Iāve been told to run engines with cap not fully locked down for a while to allow air to escape.Last Post by:
posted: 3 years ago
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CAT 3126 MUI. Leaking injector?
This topic has 2 replies, has 2 voices, and was last updated by
4 years ago January 18, 2020 at 9:25 pm I started the motors after having sat about 6 weeks and I noticed a small splattering of what I think was diesel fuel rainbow drops in the water from starboard exhaust. They cleared up/stopped after about 3 minutes at dock idle. Next day I started the motor again and no rainbow splatters. No unusual smoke at cruise and both motors seems to be running fine. I did notice this past summer that only after several hours or trolling Iād get a bit m…
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in: All Other Marine Diesels
2 RepliesJanuary 19, 2020 at 5:44 pm Yikes! Iāll wait and see. Iām Curious what the cold temperatures relationship to this problem might be? Are Injectors more prone to leaking when itās cold?Last Post by:
posted: 4 years ago
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QSB fuel burn/ load
This topic has 9 replies, has 5 voices, and was last updated by
4 years ago July 14, 2019 at 5:52 pm Can someone review my data sheet. I almost always run my boat at 2000RPM . But it is burning more fuel then the Cummins graph shows it should. I donāt care as it it very efficient but I do not want to do any long term damage. I donāt know if you can actually get an engine to burn the exact amount across the board. My data is very accurate and hardly changes with load and Sea condition. Is this typical ? 450 hour engine, all gauges are within s…
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in: Cummins Marine Engines
9 RepliesJuly 26, 2019 at 2:58 am Got to be realistic as he is running so far below the top, the engine wonāt care.. Look at the 300 MCD curve.. Same exact engine.Last Post by:
posted: 4 years ago
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When getting over the hump to planing speed smoke question.
This topic has 2 replies, has 2 voices, and was last updated by
4 years ago July 15, 2019 at 7:22 pm I recently changed props (I posted before after the info on this forum) and Iām wondering about the smoke getting on plan. Old props 4 blade 20×24 The new props are 3 blade 22×23. I think Iām getting more black and some noticeable white smoke coming onto plane (after trolling a few hours @ 850rpm) than I did with the old props. Would this be expected/normal because of the 2 inch increase in prop diameter? The motors are CATS rated 420…
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in: General Discussion
2 RepliesJuly 15, 2019 at 9:52 pm I worked with Jim @ ACME props. I was looking for better performance and range and thought my 2002 boatās stock props were not performing based on what I was reading about similar boatās with less HP motors running ACME props. The boat has 420HP 3126 MUI motors. Youāre right I need to get fuel flow numbers and see where I am on the HP curve at my cruise power setting. I picked up about 50 NM range on a 350 gal tank, which is significant and t…Last Post by:
posted: 4 years ago
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What size are my fuel hoses?
This topic has 2 replies, has 2 voices, and was last updated by
4 years ago June 10, 2019 at 9:01 am Iāve got CAT 3126 420 HP motors. The CAT part fuel hose on the governor is 3/8 inch. Would CABO put the same size line for the fuel hoses to the engine or would they up it to 1/2 inch? Iām adding a fuel flow sensor and trying to figure out what size barb setup to order. The hoses have numbers on them but no sizing info. Thanks for any help.
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in: General Discussion
2 RepliesJune 10, 2019 at 1:24 pm Thanks Rob! I was hoping those numbers would mean something to someone. Obviously I didnāt even notice the one that mattered. Great catch!Last Post by:
posted: 4 years ago
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Stack EGT drops at higher RPM?
This topic has 9 replies, has 4 voices, and was last updated by
5 years ago
May 3, 2019 at 9:11 pm Looking at the below chart I noticed the exhaust manifold temps increase steadily with engine RPM but exhaust stack temperatures decreases from 2400 rpm to 2600 rpm in the 420 And 385 HP version. All 3 HP ratings have this drop. On other boards folks comment they ādiscoveredā with EGT gauges that their motors are āworking lessā at higher RPMs due to a drop in the stack EGT. They increase RPMs at cruise to get this EGT drop thinking this is be…
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in: General Discussion
9 RepliesMay 13, 2019 at 5:03 pm The sea conditions I was in were honest 4ā seas with the odd 6 footer mixed in coming from about 8 oāclock. I could not run my normal 20 knot plane without burying the bow so I dropped down to the speed where the boat was barely in plane at about 15-16 knots to stay behind the seas. I was really going uphill on th backs of waves the entire way home. This put me in the max. Torque and heat range for the QSM for those 6 hours which combined wit…Last Post by:
posted: 5 years ago
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Prop load vs fuel burn vs overloaded.
This topic has 5 replies, has 4 voices, and was last updated by
5 years ago April 30, 2019 at 11:37 am I was rereading props move boats engines just turn them. I understand itās possible to load an engine rated at say 500 HP @ 2800 WOT rpm to produce 500 HP at say 2000 WOT RPM (overpropped) and the fuel burn in both cases should be the same as published on the manufacturers charts, correct? There is damage being done even if the engine is maintaining a proper temperature, I get that. Iām trying to understand what actually is damaging the engine…
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in: General Discussion
5 RepliesMay 3, 2019 at 9:25 am Anybody ever here of this company and itās fuel flow options? https://shop.interactio.co/collections/frontpage/products/4-optio-fuel-wireless-flow-sensors-twin-diesel-bundleLast Post by:
posted: 5 years ago
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Alternator Overheating
This topic has 10 replies, has 4 voices, and was last updated by
5 years ago April 19, 2019 at 12:08 am G’day Out cruising today and smelt a weird smell on my Cummins 6BTA 5.9, had closer look and it was coming from the alternator. Took a temp reading and it was 109c the port was 87c………. Any ideas or am I in for a new alternator Thanks
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in: Cummins Marine Engines
10 RepliesApril 24, 2019 at 3:52 am Pierre, DVM = digital voltage meters. Here’s the article I was referencing. Looks like you have a nice setup. Just need to be 100% aware as to how it works, how’s it’s wired in and what it can (and cannot tell you). https://www.sbmar.com/articles/installing-digital-volt-meters-dvm-boat/ How about some more pics and info on the boat …. it looks like a beauty.Last Post by:
posted: 5 years ago
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Let\'s all take a moment
This topic has 1 reply, has 2 voices, and was last updated by
5 years ago April 15, 2019 at 7:24 pm Seaboard Forums, I spent the entire afternoon watching in disbelief as Notre Dame in Paris France burned. As I reflect on life, I am struck by the simple fact that everyone here on the forum are able to enjoy one of the most amazing joys of life. A day on the water. No mater how much we lament a particular challenge we should all take stock and appreciate what we have. The ability to spend time with our families and loved ones on the water. To…
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in: General Discussion
1 ReplyApril 16, 2019 at 7:25 am Well said Steve. Thanks.Last Post by:
posted: 5 years ago
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Is an EGT alarm a better overheat indicator than coolent temp.
This topic has 14 replies, has 7 voices, and was last updated by
5 years ago January 28, 2018 at 5:10 pm Iām considering installing EGT gauges with alarms to augment my coolent temp gauges/alarms. Iām thinking this is an overall better heads up that things are heating up. Iāve read that if you lost all coolant (blown hose) you may not get an alarm due to sensors no longer submerged in coolant. Am I thinking corectly? Is it worth installing these? Any strong opinions? Thanks! Joe
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in: Instrumentation & Electronics
14 RepliesApril 13, 2019 at 10:23 am IMO, in a Marine application using Cummins mid-range engines ( and probably most others) , the most import alarms you have can would be redundant coolant temp ( a tad below 200F) and seawater flow. How you do that is totally up to you but this site shows may options/pics.. Tony..Last Post by:
posted: 5 years ago
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Update: ACME prop swap and performance results.
This topic has 2 replies, has 2 voices, and was last updated by
5 years ago April 11, 2019 at 8:24 am I have CAT 420 HP @ 2800 rpm. 1 3/4 inch shaft, 1:48 trans. I had 4 blade stock props, 20 x 24. Not sure of cup. Old props WOT 2850 with laser tac. I included my low tec test results below. Sea trialed props on the same day, old props and bottom cleaned day before. Looked great when hauled. Boat was loaded with full fuel and water but just me, probably up to 1500lbs missing from normal trip weight, crew, ice and bait tank water etc. Jim @ ACM…
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in: General Discussion
2 RepliesApril 12, 2019 at 7:09 am Interesting results to say the least. When I bought this boat 4 years ago I had the original props pulled and sent to prop shop, class 1. I monitored the performance of the boat over these past few years and my mileage has been about .85 NMPG. I wonāt know for sure until I do several trips what eal world burn now is. If I use CATs GPH burn numbers at 2200-2300 rpm and the new props boat speed Iām looking at 1 NMPG. Pretty impressive range in…Last Post by:
posted: 5 years ago
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Testing a generator siphon Break
This topic has 9 replies, has 3 voices, and was last updated by
5 years ago February 18, 2019 at 9:51 pm Saw a sticker saying I need to test the syphin every 6 months. How do I do this and do people really check their syphins every 6 month? How do they stop working?
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in: General Discussion
9 RepliesMarch 6, 2019 at 6:44 pm Thanks Rob! I put a copy in my boat file.Last Post by:
posted: 5 years ago
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Cleaning crankcase breather
This topic has 1 reply, has 2 voices, and was last updated by
5 years ago February 18, 2019 at 9:57 pm My motor manual says I need to clean the crankcase breather element with a non flammable liquid. What would that be, simple green? Any other suggestions? Manual says oil seal can leak if it isnāt cleaned. Is this due to over pressure if the breather canāt breath?
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in: General Discussion
1 ReplyFebruary 27, 2019 at 7:42 pm Simple green would work well… or Dawn… something like that… then let the breather element “sun dry”…Last Post by:
posted: 5 years ago
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QSD4.2 – Low RPM WOT
This topic has 10 replies, has 5 voices, and was last updated by
5 years ago February 20, 2019 at 2:35 pm Hi All, We have a Back Cove 30′ powered by a single Cummins QSD4.2 (350HP). RPM at WOT is 400 revs below factory spec, and we’ve seen progressively lower WOT RPM over the past six months. I’ve done a sea trial with a mechanic, and we don’t have a clear path about what to do next. I’m interested in your advice, and I’ve read the great low power troubleshooting article. Some details: Factory WOT is 3850 RPM Ac…
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in: Cummins Marine Engines
10 RepliesFebruary 22, 2019 at 8:05 pm Adam, I’ll give you two answers, but both are really the same.. 1) You either have not read the “Propeller moves boat” article, or you did, and you do not understand the base principle in it.. and / or 2) You are in denial Don’t worry, you are not alone.. As I said, this is your call from here fwd and the numbers you posted do not lie… Do you believe 1+1=2 ? Think about it…. TonyLast Post by:
posted: 5 years ago
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Intermittent not reaching high cruise RPM
