Cummins 5.9L 370hp B Series Mechanical vs QSB electronic

IanBat

IanBat

New Member
Nov 19, 2011
2,297
Sydney, Australia
Boat Info
Pro Tournament 36' 1999
Engines
Twin Cummins 5.9L 370hp B Series
Hi Guys,

In the search as your aware for a new boat. Looked at one two weeks ago had 5.9L 425hp QSB's dropped in, in 2006. Inspecting a boat on Tuesday, has 5.9 370hp, B series, dropped in, in 2011.

JUst want some thoughts, experiences on the older mechanical series motors compared to electronic motors.

Both are Riviera flybridges, same hull and configuration, both sets have done approx 1,000 hours.

As a diesel mechanic, but not working on the tools now for nearly 30 years, and being out of service management for just on 20. I have my thoughts and preference, which is non-electronic.

As i said though, would just like some thoughts..............oh and before anyone asks, difference in the price of the boats is 60K....both same year manufacture


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I have owned Mechanical "C" series engines for 6 years years and now i am on to the electronic version of the same motors, QSC8.3. Both variants have been very reliable motors. Ofcourse the electronic versions burn cleaner and give you a full digital picture of what is going on with the motors if they have the Vessel View. So if you have good cummins support, i would favor the electronic QSB version.
 
You can't go wrong with the mechanical b series. That engine will stay running even with a total electrical loss. I have the 330hp version and love them. At 370hp I would not worry as your not going to run them at max power anyway.
 
Last edited:
kevin27 said:
At 370hp I would not worry as your not going to run them at max power anyway.
Click to expand...

Im figuring that, as on cruise, i would be sitting at around 21-2200RPM, particularly after discussing the prop set ups, and cruising speed with the maintenance engineer in charge of the boat


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I've run both in different hulls. I really couldn't tell a lot of difference in the rpm ranges where you would normally run the engines. I"m in a large marina owned by the Sea Ray dealer and every owner of a QSB or QSC has at one time or another had to make a run home with the engines in guardian or "get home" mode. In nearly every case, the issue was easily solved by resetting the ECM, sometimes by just turning off the battery switches, other times it required a Cumins tech and a computer access to the Cummins system. This became a big enough issue that the marina sent one of the more experienced mechanics to Cummins school and got the Cummins diagnostic software for one of their laptops so they don't have to wait for Cummins any more. In 2-3 cases there was just a bad sensor that needed to be replaced.

My personal opinion is that even though Cummins engines are very dependable, the way Cummins gets the high horsepower ratings out of the old B series block is to just burn more fuel. They do that by increasing the max RPMs and precise control of fuel injection. I think the jury is still out on longevity when you turn a B series engine over 3000 rpm. Besides, as Kevin said, you will very seldom use the added horsepower in a QSB because you will cruise the engines at a lower RPM than where the QSB adds hp to the old 6BTA configuration.

True, the QSB starts more cleanly and with less smoke, but the 6BTA isn't known to be a "dirty engine" anyway. If one smokes, there is usually a reason for it that requires diagnosis and repair.

Finally, I admit that I am old school, but I don't relish the thought of chugging home from 75 miles out at 1000 rpm in guardian mode, just because the computer need to be reset or a sensor gives out of tolerance readings. With a mechanical engine, you can verify the oil pressure and temperature on the engine mounted gauges and keep on with your trip. With an electronic engine, the ECM makes that decision for you because you can't run faster than the computer will let the engine run. Generally, if a mechanical engine will start and run up to full power, there is better than "ivory soap" (99 and 44/100%) chance that you are going to get home under full power. The only reason you won't would be because of a broken part, poor maintenance or dirty fuel.

Given the choice between the 6BTA and QSB in this situation (Australia) I pick the 6BTA.
 
The 6BTA is a great engine, but beware the well known piston problem with the 370 HP version. Cummins went through 3 piston designs before getting it right on that engine. Early production engines, when run at WOT, had a habit of the #1 or #6 piston "grabbing the wall", followed by a loss of power and a lot on black smoke. Naturally a major rebuild is the outcome. Apparently the early pistons resulted in a "cooling system/lubrication problem". I should add that not all 6BTA-370's from the factory had this problem. So I would check the engine history and serial numbers with Cummins prior to purchasing this boat.
 
Thanks Frank, confirming my thoughts. As an Army apprentice, I spent 3 Months in the Cummins Workshop in Sydney on detachment. For some reason the engine shop liked me, and hung onto me as long as they could, I think they finally sent me to the Truck shop for a couple of days......
But i spent nearly 3 months, rebuilding Turbo's, cylinder heads, and a good month in the fuel room, on Injectors and fuel pumps. So I have a strong affinity with the cummins motors.
The ECM's of the new motors was part of my concern, as your probably aware I do a bit of cruising and a lot of fishing, our trips take us 40Nm Plus, off shore, and I regulalry seem to run this back in the dark.....the risk if running back with a motor down is something I like to minimse.
I also not an interview here recently with Bill Barry Cotter, one of the most respected names in Australia in building crusiers, he commented on wanting to fit non-electronic motors for reliability.
Also recently in Port Douglass, we went out on a Cat to the reef, to go diving, My brother in law and myself ended up in the Bridge chatting with Skipper and the Engineer. They mentioned they were building a couple of new boats into the Quicksilver fleet, and they were going Caterpillar engines, as it was the only motors they could source that were still mechanical, and they wanted the reliability.

Thanks, Jacob, I will check engine block numbers, I am presuming these will be right, they were installed in 2011


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I cruise my engines most of the time at 2275 rpm. That gives me about 21kts. Only a few times have I ever cruised over 2400 rpm only to outrun a storm. 2475 rpm gave me almost 25kts and at a loaded weight of 26k lbs I figure that's not bad. Fastest enough for me. What is also good is they run great at 1900rpm and gives me about 17.5kts when its rough. I have I think about 1475 hrs on mine. After cooler maintenance is not difficult or very expensive but extremely important. Mine get taken apart cleaned,tested,and new o rings every 2 years. I had to replace both after I bought the boat due to lack of proper mtc. Cost $6k. Also the factory seawater pumps are crap. Get the Seamax pumps. That is another $1500.
 
fwebster said:
I've run both in different hulls. I really couldn't tell a lot of difference in the rpm ranges where you would normally run the engines. I"m in a large marina owned by the Sea Ray dealer and every owner of a QSB or QSC has at one time or another had to make a run home with the engines in guardian or "get home" mode. In nearly every case, the issue was easily solved by resetting the ECM, sometimes by just turning off the battery switches, other times it required a Cumins tech and a computer access to the Cummins system. This became a big enough issue that the marina sent one of the more experienced mechanics to Cummins school and got the Cummins diagnostic software for one of their laptops so they don't have to wait for Cummins any more. In 2-3 cases there was just a bad sensor that needed to be replaced.

My personal opinion is that even though Cummins engines are very dependable, the way Cummins gets the high horsepower ratings out of the old B series block is to just burn more fuel. They do that by increasing the max RPMs and precise control of fuel injection. I think the jury is still out on longevity when you turn a B series engine over 3000 rpm. Besides, as Kevin said, you will very seldom use the added horsepower in a QSB because you will cruise the engines at a lower RPM than where the QSB adds hp to the old 6BTA configuration.

True, the QSB starts more cleanly and with less smoke, but the 6BTA isn't known to be a "dirty engine" anyway. If one smokes, there is usually a reason for it that requires diagnosis and repair.

Finally, I admit that I am old school, but I don't relish the thought of chugging home from 75 miles out at 1000 rpm in guardian mode, just because the computer need to be reset or a sensor gives out of tolerance readings. With a mechanical engine, you can verify the oil pressure and temperature on the engine mounted gauges and keep on with your trip. With an electronic engine, the ECM makes that decision for you because you can't run faster than the computer will let the engine run. Generally, if a mechanical engine will start and run up to full power, there is better than "ivory soap" (99 and 44/100%) chance that you are going to get home under full power. The only reason you won't would be because of a broken part, poor maintenance or dirty fuel.

Given the choice between the 6BTA and QSB in this situation (Australia) I pick the 6BTA.
Click to expand...

Frank

In my case since I own the QSB 425's. What can be done from a preventative maintenance stand point to reduce issues with these motors.
 
The issues with having the engine derate its rpms/power where you end up in limp home mode is not a maintenance related issue. It seems to only occur in newer engines that are not yet broken in and most owners don't experience significant problems with derating more than about once a year and the problem is usually not much more than a bad sensor. Mechanically both the QSB and QSC seem to be very reliable. Keep an eye on your engine temperatures and if you see any unexpected rise, figure out why and fix it (usually fouled after coolers or heat exchangers). Other than that, keep the coolant checked for SCA's and follow Cummins maintenance recommendations.
 
B series engines do not need to run SCA's in the coolant as they are parent bore engines and don't have the same issue with cavitation of coolant on the liners like the C series or any engine that has wet liners. You can run it, but it is not necessary. As on any boat engine, salt water side should be cleaned and watched closely. Aftercoolers should be removed and cleaned every 2-3 years depending on the water you boat in normally. AS Frank stated above, watch the temps and make sure you are not overloading the engine. Overloading will lead to an early death. I know Frank has discussed this many times on here so I'm sure you all have heard this before. Clean fuel, clean fuel, clean fuel.
 
Could you define "overloading" the engines? I run 70-80% load max. Maybe ran full throttle for 15 min out of 82 running hours this year.
 
fwebster said:
The issues with having the engine derate its rpms/power where you end up in limp home mode is not a maintenance related issue. It seems to only occur in newer engines that are not yet broken in and most owners don't experience significant problems with derating more than about once a year and the problem is usually not much more than a bad sensor. Mechanically both the QSB and QSC seem to be very reliable. Keep an eye on your engine temperatures and if you see any unexpected rise, figure out why and fix it (usually fouled after coolers or heat exchangers). Other than that, keep the coolant checked for SCA's and follow Cummins maintenance recommendations.
Click to expand...

Frank, I sent you a related question in a PM


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trit21 said:
B series engines do not need to run SCA's in the coolant as they are parent bore engines and don't have the same issue with cavitation of coolant on the liners like the C series or any engine that has wet liners. You can run it, but it is not necessary. As on any boat engine, salt water side should be cleaned and watched closely. Aftercoolers should be removed and cleaned every 2-3 years depending on the water you boat in normally. AS Frank stated above, watch the temps and make sure you are not overloading the engine. Overloading will lead to an early death. I know Frank has discussed this many times on here so I'm sure you all have heard this before. Clean fuel, clean fuel, clean fuel.
Click to expand...


Also what are SCA's?
 
Supplemental Coolant Additives. When coolant analysis shows your coolant is loosing its effectiveness, it may call for the addition of SCAs to restore the coolant's effectiveness.
 
SCA is just an additive that is obviously added to the coolant. The purpose of the additive is not to cool the engine or make it more efficient but the purpose is to stop the coolant from cavitating when it is in contact with the very hot liners of the pistons. When the coolant cavitates when in contact with the lines, a small air bubble is formed which can then damage the liner. Overtime, this could lead to premature failure. If you don't have liners, you don't have to worry about this problem. B series engines are parents bore, C series engines have liners. Uness they have changed something in the B series when the newer QSB was introduced but I don't think that is true.

Overloading an engine has to do with reaching over max RPM and allowing the engine to breath without laboring. Load the boat down like you would for a long distance cruise, full everything, fuel water, food people, gear etc etc. Take boat out and ensure it can reach over rated RPM. Lets say your engines are rated at 3000 RPM, you should be able to reach over rated RPM loaded for bear, 3070-3150 or so. If when loaded heavy, you cannot reach over rated RPM, then you are overloaded and all RPM you are overloaded since you will be drawing more fuel at specified RPM than the published fuel demand curve, published by Cummins, Cats etc for every motor. I'm trying to make this quick as I know Frank has discussed this but if you need a longer slower explanation I can provide that OR you can visit boat diesel and get the same information by reading the forum over there OR even on SBMAR.com website.
 
trit21 said:
SCA is just an additive that is obviously added to the coolant. The purpose of the additive is not to cool the engine or make it more efficient but the purpose is to stop the coolant from cavitating when it is in contact with the very hot liners of the pistons. When the coolant cavitates when in contact with the lines, a small air bubble is formed which can then damage the liner. Overtime, this could lead to premature failure. If you don't have liners, you don't have to worry about this problem. B series engines are parents bore, C series engines have liners. Uness they have changed something in the B series when the newer QSB was introduced but I don't think that is true.

Overloading an engine has to do with reaching over max RPM and allowing the engine to breath without laboring. Load the boat down like you would for a long distance cruise, full everything, fuel water, food people, gear etc etc. Take boat out and ensure it can reach over rated RPM. Lets say your engines are rated at 3000 RPM, you should be able to reach over rated RPM loaded for bear, 3070-3150 or so. If when loaded heavy, you cannot reach over rated RPM, then you are overloaded and all RPM you are overloaded since you will be drawing more fuel at specified RPM than the published fuel demand curve, published by Cummins, Cats etc for every motor. I'm trying to make this quick as I know Frank has discussed this but if you need a longer slower explanation I can provide that OR you can visit boat diesel and get the same information by reading the forum over there OR even on SBMAR.com website.
Click to expand...

Thanks for the great info. I will take the longest explanation you have time to provide. I am new to diesel power
 
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