Official Cummins QSC-500 Thread

Just returned from maiden voyage with 2006 44DA QSC 500's purchased last fall. During the winter, had all maintenance performed (aftercoolers, heat xchangers, etc.) to bring engines in line with Cummins requirements. All readings seemed fine except GPH burn. Stbd reading was approx 3-4 GPH higher than Port during most of the trip. I have researched and read many of the posts on this thread which are quite helpful. I am only speculating, but could the issue be a faulty sensor? If this could be indicative of something else, then I will promptly arrange for visit from local engine tech. The boat ran fine otherwise. Thanks. Frank C.

My port engine is always 1 gph more. Throttle and load are exact .
 
Anyone know what this is? Located just after the turbo on the exhaust.
 

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Exhaust outlet temperature switch.
 

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Exactly. Mine looked similar to yours when we purchased our boat. Cost me $245, and found it online down in Louisiana
 
Thank's prkeyes and TNT8808. Accidentally broke the lead off while servicing the port engine and generator Raycors. So much for saving a few bucks by not paying the marina to do the service.
 
Mine has been broken for two years. The stb side takes a beating during service … (ive replaced it 2 x already )

So ill just be extra cautious

Rob
 
I soldered one of the terminals back on that had broke off and has worked fine ever since. However this summer I had the port side go bad, it sends a high temp warning to the Smart Craft unit. Replacement cost was $260 for that little sensor.
 
Anyone know where the turbo boost sensor is located. IDK how often u guys scroll tru the Smart craft display while under way.. im pretty on top of it ... looks like i got a sensor issue . its ready 46 Psi .. normal is 26..also the dead give away is at idle its reading 10

Thanx

Rob
 
Air Filter cleaner. Just curious if everyone replaces their air filters with Cummins or go with something else? Also is there a cleaner to clean or do they always need a new replacement? Wondering about my options.
 
Has anyone replaced their sea water pump inlet elbow with a 90 degree fitting? On the 44DB, the port engine pump's inlet hose is oriented aft with the hose itself approaching the engine from the front which requires the hose to make a 180 degree ridiculously tight turn to connect to the pump. The hose I was able to find will not make the turn in the available space. The 45 degree fitting interferes with the engine mount stringer if it is turned to meet the hose directly. The simple remedy would be to install a 90 degree fitting and orient it forward. I've tried SB Marine but they don't offer it and foe some reason can't order one. I've scoured the web and have not found a source yet.
Any ideas would be greatly appreciated.
Rusty
 
All
I will be surveying my first potential diesel boat in a couple weeks. I have been trying to read everything I can to get a better comfort level with diesels as I have only owned gas. I have had many comments from diesel owners on here telling me they are great and once I get them I won't regret it. So, with all that said, and after reading many posts, it appears that there is always something going wrong with diesel engines! Bad sensors, fuel issues, belt issues, etc. When I owned gas boats, it was pretty much set it and forget it. I did the normal maintenance, but never once had an engine fail on me or even an erratic gauge reading. So I am a little confused about why, outside of fuel economy and torque, that diesels are so much better than gas. Are they that temperamental? Do they require constant repairs and monitoring and maintenance? I am fine with doing normal maintenance and understand that they use more oil and the filters are more expensive and all that, but I don't want a boat that i have to worry more about working on it than enjoying it! Would appreciate comments on the above.
Thank you,
Rob
 
Rob, I'm sure I see far more MX related issues posted on the forum with gassers than diesels. You see a lot of posts here with folks sharing their issues but I don't think its even close when compared to the problems there are with gas engines. There does seem to be more of a cloak of fear that is cast over the diesel engines due to the fact that there are fewer diesel mechanics out there and the factory service guys are expensive. If you are mechanically inclined and educate yourself you will have no problem keeping your engines in good operating condition. I know I enjoy having the diesels way more than my last gas boat. I was apprehensive at first like you but it did not take long to fall in love and sleep soundly having gone the diesel route.
Relax and enjoy
Carpe Diem
 
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To me the scary part of moving to the Diesel is the initial unknowns vs what many people take for granted on the gas engines because they are used to them.

In the 35-40 foot boat range there are many pro's and con's to gas vs Diesel. Once you go over 40' to about 45' the pro's of Diesel really start to shine, once over 45' you have virtually no choice but Diesel.

As it appears your looking at a 44DB that boat would not be a good boat as a gas, I think they put gas in the 37DB and the fuel consumption on that was massive.

Diesel's cost slightly more to maintain than gas but mostly because the size. A QSC takes 4.5 gallons of oil on an oil change - heck the filter takes 3/4 gallon on it own to prefill. The oil filter is 3-4 times bigger than the average gas oil filter. There are multiple fuel filters, again all much bigger than a gas engine.

The fuel savings will make up for that difference.

The scary part of Diesel's is when something goes boom. The parts are very expensive and can have many hours of labor to remove/replace. The good news is a well cared for Diesel is very unlikely to go boom. Prop it correctly, feed it clean fuel and keep up with recommended maintenance and it will run forever in a cruising boat.

The sensor issues you mention are more common on the QSC (which is probably what is in the 2006 44DB). Cummins made three variants of the 450 to 500hp engines that are in the 42 and 44 Sedan Bridges and Sundancers from 2003ish and later.

The 450 "C" is the oldest, all mechanical systems. Basically once its running it just needs fuel and air.

The 480 "CE" is the bridge between the 450 C and QSC-500, its the same block as the 450 C but uses an electronic controller to meter the fuel delivery. These are the most prone to failure as they should never have rated these at 480hp, it is suggested to prop them the same as the 450 C for long life. This engine is still mostly mechanical except for the fuel system so its easy to fix and does not have as many sensors to break.

The QSC-500 is a totally different engine, to the 450C/480CE. Every aspect of the engine is controlled electronically from the throttles, to fuel and air. Because of that it uses a bunch of sensors to control it and they can and will fail. When one does the motor goes into "guardian" mode and you will limp home. Failure happens but its not common.

The advantage of the QSC is it is nearly smokeless in operation, only on 45 degree and lower days will you get a faint whiff of smoke (but not see it) for the initial startup. Other than that no smoke at all. For me that is ultra important as my wife hates the smell of diesel smoke, to the point it makes her sick.


Knock on wood we have had 5 trouble free years, over 500 hours with only a failed alternator in all that time.
 
Thank you both! It is scary, but I hope I am one of those that can be chiming in as you are in a few years to the next perspective diesel owner!
Rob
 
I own CAT's, but similar parts on both.

AirSep recaptures oily blow by air off the crankcase, and recycles the air/oil back into the air intake and oil sump. On my CAT's the hoses are about 2' long and I just replaced them at about $16/foot. Easy DIY job. They dont wear out very often, but can crack due to age, or in my case, become oil logged.

The boost hose is likely a piece of hose that carries the heated and pressurized air from your turbo outlet to the after cooler. If they rupture, you don't get your turbo boost and lose power. Those also can and should be replaced. I'd have to defer to a Cummins owner to see if thats a DIY job or not.

Here's the Walker Air Sep Page https://www.walkerairsep.com/product_detail.asp?id=613

Dave, which hoses did you replace and where did you get them?
We’re they the ones that run between the vacuum regulator element and airsep.
 

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