Official Cummins 6cta 450C thread

FeLizDream

Active Member
Jun 28, 2015
253
Marco Island Marina Yacht Club, FL
Boat Info
2001 Sea Ray 400 Sedan Bridge, with engine synchronizer.
Engines
Cummins 6cta 450 HP, prop 22 Lx 22" L cup.
I couldn't find any thread for the Cummins 6cta 8.3, 450 C also known as Diamond so I,d like to start a new thread for this beautiful engines. I found information in this fantastic page all over, but with this thread I would like to have it all together in one simple thread. Hope you like it and help this thread start going on...

To start I would like to put all the information regarding maintenance,
This is a Marine Maintenance Part List from Cummins engine manuals, I am going to list parts and serial numbers:

Drive belt: 3911587
oil filter: LF 9009
Fuel Filter: FF5285
Air Filter: AH19002
Coolant Filter*: WF2071
Raw Water Impeler: 3897337
Zinc Plug: 68241

Engine rating 450 hp@ 2600rpm fuel pump: 3866799

Oil Engine:
use a high quality Multi-Viscosity SAE 15W40 (Cummins Premium Blue)
in Cold Climates: 10W30

Engine Coolant: use high quality Ethylene Glycol mix in ratio 50/50 water to glycol solution

The oil pan capacity is: 13.2 liters or 14 quarters ( always check level)

Basic engine Data is:
450C rpm 2600 fuel pump Bosch 23.3 fuel consumption

 
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FeLiz, Nice thread. I do not have Cummins but this thread is a good idea. 450 hp on the 400 SD sounds like a very sweet match. JC
 
Great idea!....I've had a pair of these for 5 years and they have been awesome. Absolutely no issues, best boat engines I have ever had. 1,550 hours and growing. Would love to hear other's experiences and learning. What is the recommended transmission fluid change interval? First few times, I changed it with engine old (100 hrs), but oil looked brand new. Last few times, was 200 hours. Still looks like new.

I 've been pulling the aftercoolers every 2 years per BD recommendation, but they have looked great in the past. Should have pulled them this year, but I'm going to wait one more year. Strb engine is extremely difficult to do. Comments?
 
My Cummins engines have the ZF280A transmission, ZF recommends SAE 30, I went last week to the ZF Dealer in Miramar, FL and the engineer told me, if I have the Boat all the time in South Florida (tropical climate) I should use motor oil SAE 40 instead. So in my next oil change I will start using SAE 40.
 
Here are a few things I've learned:

- Air separators are made by Walker Engineering. Clean big filter every 250 hours. Replace after 1000 hours. I proved this because at right on 1000 hours mine were still clogged after cleaning and starved the engines from enough air to shoot black smoke out the exhaust. Factory install is 8" filters, but my last chat with Walker they recommended 9" now for the 6CTA to ensure enough air even when filter is dirty. I replaced my 8" with 8", though.

- Seaboard Marine (sbmar.com) specializes in Cummins Marine engines. I buy most all my maintenance items from them and they have many "how to" articles. I also replaced my factory Sherwood seawater pumps with their SMX pumps. I also bought an alternator from them (and a starter, which it turns out I didn't need afterall). Factory alternator is 135amp. I replaced with 160amp alternator. If your air intake grid heater is in working order (neither of mine are. I disconnected them since I live in the coastal south - ha!) then you will definitely want the 160amp alternators. The grid heaters draw a lot of current and can contribute to early alternator failure.

- I have settled on 2100rpm as the ideal cruise rpm for these engines. That's just a hair over the 80% of the rated 2600rpm max. I know some that run them as high as 2250rpm at cruise and a few that run at 2000rpm. 2200+ scares me as too high for continuous cruising. When I want to save fuel and enjoy the ride trawler style, I sit right on 1000rpm.

- I had to do a lot of painting touch-up on my engines. If you can't find Cummins White, I found that Rustoleum Canvas White in the spray can is virtually a perfect match. I also have mixed up the Rustoleum white and almond 50-50 to get the brush on version of the same Canvas White.
 
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Here are a few things I've learned:

- I have settled on 2100rpm as the ideal cruise rpm for these engines. That's just a hair over the 80% of the rated 2600rpm max. I know some that run them as high as 2250rpm at cruise and a few that run at 2000rpm. 2200+ scares me as too high for continuous cruising. When I want to save fuel and enjoy the ride trawler style, I sit right on 1000rpm.
ZZ13, I've only had my 6CTA Cummins one season and I've been cruising at 2,300rpm. I've done this based on some info in SeaRay literature and this notation at the bottom of my Performance Curve spec sheet. I hope I'm not abusing anything.

Intermittent Rating: This power rating is intended for Intermittent use in variable load application where full power is limited to two (2) hours out of every eight (8) hours of operation. Also, reduced power operation must be at or below 200 RPM of the maximum rated RPM. This rating is an ISO 3046 fuel stop power rating and is for applications that operate less than 1500 hours per year.
 
If you can't find Cummins White, I found that Rustoleum Canvas White in the spray can is virtually a perfect match
I'll try that paint. I sprayed my last can of Cummins White: 3885912

ZZ13, I've only had my 6CTA Cummins one season and I've been cruising at 2,300rpm. I've done this based on some info in SeaRay literature and this notation at the bottom of my Performance Curve spec sheet. I hope I'm not abusing anything.

The critical number is that you can spin the engines beyond the minimum spec 2600. If not, you're overloaded and running the exhaust too hot. My fast cruise is 2200 / 24 kts
 
You guys with Cummins Power should visit and join BoatDiesel.com. This will be the best $25 you ever spent on you boat. From the conversation and questions, I'm guessing that the majority of you are over propped. Please do yourself a favor and do this. The results of too much pitch can be more costly than you ever could believe. We Cummins owners have the advantage of a VERY knowledgeable gang at Seaboard Marine in Oxnard, California that has what we need. Helped me keep mine running great for 20 years.
 
You guys with Cummins Power should visit and join BoatDiesel.com. This will be the best $25 you ever spent on you boat. From the conversation and questions, I'm guessing that the majority of you are over propped. Please do yourself a favor and do this. The results of too much pitch can be more costly than you ever could believe. We Cummins owners have the advantage of a VERY knowledgeable gang at Seaboard Marine in Oxnard, California that has what we need. Helped me keep mine running great for 20 years.


Agreed 100% - its a no nonsense site, with great information. My engines are much happier after reducing pitch.....I took 1.5" out
 
Agreed 100% - its a no nonsense site, with great information. My engines are much happier after reducing pitch.....I took 1.5" out
Are you down to 22.5? Mine are still at factory level of 24 pitch. I go 2650rpm at WOT. What are the indicators that your engines are "happier"?

bigcam, why do you think the majority of us are overpropped? By the way I concur on boatdiesel and Seaboard Marine. I am actively involved with both.
 
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Before change, I'd start off the season turning 2580, and the minimal growth at the end would reduce me to 2550. I wanted 2700, and reduced the prop to 22.5" This put me close @2680 WOT - I can live with it. I'm very comfortable cruising at 2200/24kts now.
 
Before change, I'd start off the season turning 2580, and the minimal growth at the end would reduce me to 2550. I wanted 2700, and reduced the prop to 22.5" This put me close @2680 WOT - I can live with it. I'm very comfortable cruising at 2200/24kts now.
That's good. So 1.5" got you 100rpm. I take it that's with full fuel tanks.
 
I have always wondered this and never looked into it. Why are there two t-stats on each engine? Is it redundancy or are there two separate cooling jackets on the engine?
 
Great thread! I have the 480CE which is really the same engine with the first attempt at computer control. I have gone through the overprop issue from Sea Ray. my factory props were 23x27 4 blade hytorq. After a dropped valve seat in the stbd. engine I was advised via boat diesel to take out two inches of pitch. I did that but found I was then under propped. Ultimately I switched to new Acme's. During this process I found out that Sea Ray used a large amount of cupping. .130 I was told that each .030 of cup would result in 45 rpm. So if anyone is looking at a re-pitch have your prop guy check the cupping as well.
 
So is it trying to be said here that Sea Ray knowingly designed and delivered boats that would eventually burn up your engines if you didn't immediately go change the factory configuration???

They have an article on this on their website. They say boats are equipped for "general use under normal conditions and load". So filling up all your tanks isn't considered "normal load". They also then in all caps scream not to use propellers that operate engine at rpm lower or higher than recommended WOT rpm by engine manufacturer.

So, are there any stats on percentage of delivered boats that have broke due to factory "incorrect" props?
 
I have always wondered this and never looked into it. Why are there two t-stats on each engine? Is it redundancy or are there two separate cooling jackets on the engine?
I just replaced my t stats, and the are in the same water jacket.
 
I cannot completely answer your questions. Sea Ray says the dry weight for my boat is 28,000 lbs. I have no idea what the test weight is for their prop selection. My boat is closer to 35,000 lbs with the hard top and fluids. Even more when loaded for a long trip. I would suggest that Sea Ray like any builder would want to put out the best numbers for their products. Yes, I think that that may be less than ideal for the engine longevity.
 
Has anyone replaced their t-stats? Sure looks like I have to remove the belt to remove the alternator bracket before I can go at the four bolts holding the t-stat housing down. Is that correct?
 
Has anyone replaced their t-stats? Sure looks like I have to remove the belt to remove the alternator bracket before I can go at the four bolts holding the t-stat housing down. Is that correct?
Yes. Expansion tank, alternator bracket, and idler pulley (torx) all need to be removed. Youll find one bolt is tricky, and needs to come out with the alt bracket. I was able to lose and swing the alternative away without removing wires.
 

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