44 DB QSC Engines
- Thread starter Greg Peck
- Start date
- Jun 30, 2023
- 368
- Boat Info
- 2007 44 Sedan Bridge, Raymarine chart plotter x 2, radar, sounder, auto pilot, Starlink.
- Engines
- Cummins QSC-500's
I have an ‘07. The QSC-500’S haven’t let me down. They are electronic controls so it’s not like old days where you could McGyver a temp fix to get home. I keep some spare sensors on board just in case but haven’t needed them. My only real complaint is that the zincs in the port side fuel/oil cooler are a real chore to replace.
I have a QSC 600 in my boat. Can confirm that aft fuel cooler zinc is a dog to replace. The way my engine is mounted on the stringers, it requires a VERY specific sequence of motions to get the wrench on the bolt so it can be turned.
Other than that, its been relatively easy to work on and reliable. The aftercooler is a bit more cumbersome to work on vs. a QSB because its in the middle of the loop vs. right off the water pump outlet, and needs multiple gaskets and O-rings to be replaced when servicing. I do kinda wish the oil filter was a more convenient location, like next to the fuel filter like on the QSB. It's not hard to change it but you have to be careful to not spill the 3 liters of oil it holds.
Because its its an electronic common rail, bleeding the fuel system is dead simple making fuel filter changes a breeze. Just key on the engine a bunch of times an it automatically primes the filter.
bmac
Well-Known Member
- Jan 11, 2008
- 1,845
- Boat Info
- 2006 58 Sedan Bridge, Walker Bay Generation 390 RIB w/40hp Yamaha, 2014 Wellcraft 232 CC w/Yamaha
- Engines
- MAN 900 CRM
I thought my 44DB with the QSC500 was underpowered but I only thought that after having a 52DB and 58DB; those boats flew compared to the 44 with QSC. I would characterize the hull/engine combo as adequate, it certainly doesn't suck.
I would just strongly suggest you to get the engine RPM vs. fuel burn data during the sea trial so you can compare that actual fuel burn to the Cummins published performance chart.
For the long-term health of the engine it's important to not overprop the boat, and thereby prevent excess load on the engine. From what I've read here from other owners, Sea Ray had a tendency to overprop some models in order to hit desired speed targets for a particular engine. If the boat hits a speed you like but is over propped it will damage the engine. If you take some pitch out of the prop to get the fuel burn under the spec curve it will slow the boat down, possibly to a level you won't like.
Here's a link to the performance curve for a QSC 500.
And an excerpt from the file.
In a nutshell, you want to be sure that your fuel consumption for a given RPM does not exceed what Cummins has published in this chart. If it does, the boat is over propped. The idea way to check is on the sea trial have the captain step to each RPM level and then note the fuel burn rate (usually in gallons per hour).
This is a chart I made of of my boat's performance against the builder and the Cummins specs. It has a single QSC 600. You can see that in the middle of the curve it burns slightly more fuel than the Cummins spec (green vs. purple lines), but at cruise RPM of 2800 I'm 2 gph below. I'm not too concerned about the slight gpm excess burn in the middle because at those RPMs I'm going between 14-19 mph and I hardly every travel at those speeds.
For the long-term health of the engine it's important to not overprop the boat, and thereby prevent excess load on the engine. From what I've read here from other owners, Sea Ray had a tendency to overprop some models in order to hit desired speed targets for a particular engine. If the boat hits a speed you like but is over propped it will damage the engine. If you take some pitch out of the prop to get the fuel burn under the spec curve it will slow the boat down, possibly to a level you won't like.
Here's a link to the performance curve for a QSC 500.
And an excerpt from the file.
In a nutshell, you want to be sure that your fuel consumption for a given RPM does not exceed what Cummins has published in this chart. If it does, the boat is over propped. The idea way to check is on the sea trial have the captain step to each RPM level and then note the fuel burn rate (usually in gallons per hour).
This is a chart I made of of my boat's performance against the builder and the Cummins specs. It has a single QSC 600. You can see that in the middle of the curve it burns slightly more fuel than the Cummins spec (green vs. purple lines), but at cruise RPM of 2800 I'm 2 gph below. I'm not too concerned about the slight gpm excess burn in the middle because at those RPMs I'm going between 14-19 mph and I hardly every travel at those speeds.
