Cummins QSM11 engines. Anyone have them? How easy to reach/change the impellers?

[MV Wanderlust]

We're considering a larger boat. The model often comes with the Cummins QSM11 635 hp engines as standard equipment. Have found a few things online, such as the location of the zincs (easy to get to) and that it has a dry exhaust and dry turbo. Does anyone have experience with this engine? How accessible is the water pump">raw water pump and how easy it is to change impellers without removing the pump? Any pros/cons/tips/thoughts that I should be aware of?

Thanks.

John

[MV Wanderlust]

...and a follow up question, for anyone who has or has had these engines:

Our routine is to run at about 8.6 knots or 10 mph for good fuel economy for most of a trip. We'll get out into open water (wide river, bay, Gulf or ocean) and crank it up to about 2000 RPM for five or ten minutes to blow out the turbos and get up on plane, then slowly ease down to hull speed for the remainder of the day. How would QSMs do under such conditions? Would that kind of treatment be harmful to them?

[MV Wanderlust]

Any thoughts? Anyone have experience with QSM11 engines?

[ranger58sb]

I have not seen QSM11s...

But I'd expect the water pump is likely on one side... so changing the impeller on the side where the water pump is inboard is likely easy, changing on the other (outboard) side maybe more difficult. Probably depends more on the boat and engine room access (especially on the outboard side) than on the engines themselves.

Ditto zincs, maybe some on either side... so changing may be easier on one than on the other... again depending on engine room access.

You can maybe get service manuals from Cummins in advance, to review (although when I got manuals for ours I had to provide serial numbers). Maybe Tony Athens has info on his site (sbmar.com), or maybe there's stuff on boatdiesel.com -- both good resources for Cummins info anyway.

-Chris

[spearfish3]

We had a QSC 8.3 and it was an awesome engine. I have always admired the filter placement on the QSM 11s. Great design.

Diesel like to have a load on them to prevent issues from chronic underloading. That said, it is my understanding that the new common rail engines are more tolerant than the older mechanical engines to low RPM light loads. I would definitely bring the engines up and let them run every few hours.

[Captsteve53]

Regarding your request , actually there is a bit of an issue due to the dry exhaust system some are not aware of and more important than the location/service of the water pump:

The dry manifolds and turbos Cummins uses on the “DRY” QSM 11 do not hold up well at all if the engine if loaded much above the “535” QSM 11 performance curve (no more than 400 HP or 20 g/h at 2100 RPM) there’s just too much heat with no place to go.

1) Look at this picture below of the RED-HOT manifold. This is what is happening under your “tin-foil wrapped” exhaust manifold & turbo… excessive load = excessive heat. Just because your local “Cummins Tech” says all is good and is propped right as long as your 635 or 670 QSM is reaches its rated RPM or 2300 or a tad more, IMO, it is far from OK if you want to help prevent early exhaust manifold leaks or worse… The damage to the turbo’s and manifolds do not happen at WOT, it all happens in the 1800-2000 RPM range where most boats burn over 20 GPH, with 22-24 GPH all too common at around 1900 RPM. This is where the issue is that warps the manifolds and turbo bases.

2)All diesel engines, by design, lose about 33% of all the energy made (heat) burning fuel out the exhaust… So if you are burning 20 gallons per hour, that means the crankshaft is putting about 400 HP into the prop to move your boat forward, and about 400 HP thru the exhaust.

3)Given the high horsepower nature of the DRY QSM11 engine, it’s easy to see why engines can and usually are grossly overloaded in the 1800-2000 RPM range. It’s the high HP and/or high fuel burn at the lower RPM’s that does the manifolds & turbos in. Other that a good engine!

Reduce the load at CRUISE RPM (1900-2000 RPM) to under 20GPH (400 HP). Period

Cheers Steve

[David M]

I have a pair of Cummins B-series turbo Diesels. They are wet exhaust engines. They are rated at 315 horsepower each.

After reading what CaptSteve had to say, it makes me wonder if they can be changed out to a wet exhaust system?

Cummins says to run the engines up to full speed for half an hour once every ten hours to burn the carbon out of the combustion chambers. I have just over 5000 hours on this set of engines. They have been very reliable and I would not choose any other brand of Diesels for a larger sized power boat.

[MV Wanderlust]

Thanks for the input, everyone.

Chris, I joined sbmar.com. A wealth of Cummins information over there.

[Cheechako]

I know when we built boats with the QSB series, Cummins was VERY picky about exhaust temp, pressures and sizing in development.

[ranger58sb]

Originally Posted by spearfish3

We had a QSC 8.3 and it was an awesome engine. I have always admired the filter placement on the QSM 11s. Great design.

What's different about filter placement on the QSM11s, compared to the QSCs and the earlier 6CTAs?

-Chris

[spearfish3]

All of the filters on the QSM 11 are in the front of the engine. The QSC had them on the side.

[willpower1]

QSM are good engines. I would take one over a volvo any day of the week.

Check boat diesel dot com more marine diesel info than you could ever need.

[ranger58sb]

Originally Posted by spearfish3

All of the filters on the QSM 11 are in the front of the engine. The QSC had them on the side.

Thanks, useful info. Sounds like a good location if access to the front of each engine is easy.

Ours are on the port side of each engine. That location by itself doesn't make it difficult to change impellers. The fact there's very little space between the port water tank and the port engine (and raw water pump) is what makes it more of a challenge to change.

-Chris

[MV Wanderlust]

Originally Posted by ranger42c

I have not seen QSM11s...

But I'd expect the water pump is likely on one side... so changing the impeller on the side where the water pump is inboard is likely easy, changing on the other (outboard) side maybe more difficult. Probably depends more on the boat and engine room access (especially on the outboard side) than on the engines themselves.

Ditto zincs, maybe some on either side... so changing may be easier on one than on the other... again depending on engine room access.

You can maybe get service manuals from Cummins in advance, to review (although when I got manuals for ours I had to provide serial numbers). Maybe Tony Athens has info on his site (sbmar.com), or maybe there's stuff on boatdiesel.com -- both good resources for Cummins info anyway.

-Chris

I joined Tony Athens site (sbmar.com) and posted the same question. He not only answered, he also supplied photos of both the 6CTA and QSM11 engines and close ups of the raw water pumps. Helpful guy and great site. Link to post and photos You have to be registered and logged in to see the photos.

The short version is that the QSM11 provides fairly easy access to the back of the raw water pump. The dipstick tube and the oil filler tube are in fairly close proximity but it looks like it might be possible to work a short puller in there. Good to know.