Very slow cranking 450C Cummins

Larry

Larry

Well-Known Member
Oct 19, 2006
1,284
Oakland, NJ
Boat Info
2004 42 Sundancer
Hydraulic platform
Cockpit air
KVH M3
Engines
450hp Cummins
I have had since I bought the boat last year an issue that both my engines cranked a little slow. I replaced ALL my batteries, I have 3 Group 31 on each engine. When I used the parallel switch they cranked fast and would start right up. At the end of the season I replaced both starters just to eliminate them being an issue. This year, my Starboard motor will not crank fast enough to start even when using the parallel switch?? I guess I will start checking all connections and verify I don’t have a bad battery in the mix... Anyone have anything else to add?
 
Problems like these are a pita because it can be many things or combinations of things. You just have to go through them one at a time. Is the port cranking better this year? If so maybe you got a bad starter, but guessing that’s not the case. Check the output of your battery charger if the boat engines charge them up enough to crank good and it’s only after setting at the dock that you have trouble.
Check all the connections, and don’t forget the grounds on the engine blocks, and don’t rule out the bad battery idea, load test them or check with a hydrometer.
Continue to use the emergency start crossover until you get it sorted out as the slow cranking isn’t good for your starters or your motors. Good luck
 
I'm surprised to see group 31s being used on 450 Cummins but 3 of them should work if all 3 are in good condition and all the connections are also good. Check the cranking voltage at the starter with a digital volt meter and at the battery terminals. Have you checked the water levels in the batteries? I suspect you had the starboard batteriesz freeze over the winter and if so they are junk.
 
Larry do you know the CCA or MCA rating on the new batteries?

The previous owner replaced the port batteries on my boat before I surveyed, I replaced the starboard right after I purchased. My port always cranked slower than starboard (but not so slow as to cause concern). Didn't think all that much of it until this year when I replaced all my batteries and started looking at CCA/MCA ratings. My port batteries were right at minimum specs, my starboard batteries were 50% greater.

Looks like the 450C needs 1250 CCA or 1560 MCA, so your batteries need to be at least half that rating.

Either way sounds like your worse off this year so its either bad connection, bad battery or bad starter (unlikely).
 
My starboard QSM11 was and still is slower cranking than the port and it bothers me to no end; they always start however. Both engines' starters as well as both start relays were replaced. Still starboard cranked a bit slower. It helped a bit when the emergency start solenoid was activated but not significantly to isolate a battery problem. I swapped the batteries (8D's in my case) and the slow cranking remained with the starboard engine. It goes without saying that all of the electrical connections were removed cleaned and reinstalled with a dab of di-electric grease. I then removed the starboard main disconnect solenoid and took it apart for inspection thinking it had arcing and other issues but none were evident; the only thing I did was change the contact spring tension (which is adjustable). The mechanic then swapped the two starters and relays between the engines and still the slow cranking remained on the starboard engine. So, I pulled all of the electrical cables out of the boat (the 4/0 cables) and reterminated the ends with new lugs including new lugs for the batteries as well as inspected the cables. And still that starboard engine cranks slower than the port; albeit, it's all a bit better, actually both engines crank better. So, it ends up the positive and negative cables on the starboard motor are about ten feet longer than the port motor; that voltage drop is enough to make a difference...… So, if I was to keep batteries for starting the boat I would probably double up that positive cable to the starboard starter but towards the end of the year I moving away from batteries to start the engines.
 
I've gotten into the habit of using the ALL switch whenever I start them, figuring more power is better. Anybody see a downside to this?
 
Perform voltage drop tests on both the positive and negative circuits. Hook your volt meter to the battery post and main starter terminals while cranking. The meter should read close to zero. If showing voltage then that will be your loss. Move your leads closer together to pin point the problem.
 
ttmott said:
My starboard QSM11 was and still is slower cranking than the port and it bothers me to no end; they always start however. Both engines' starters as well as both start relays were replaced. Still starboard cranked a bit slower. It helped a bit when the emergency start solenoid was activated but not significantly to isolate a battery problem. I swapped the batteries (8D's in my case) and the slow cranking remained with the starboard engine. It goes without saying that all of the electrical connections were removed cleaned and reinstalled with a dab of di-electric grease. I then removed the starboard main disconnect solenoid and took it apart for inspection thinking it had arcing and other issues but none were evident; the only thing I did was change the contact spring tension (which is adjustable). The mechanic then swapped the two starters and relays between the engines and still the slow cranking remained on the starboard engine. So, I pulled all of the electrical cables out of the boat (the 4/0 cables) and reterminated the ends with new lugs including new lugs for the batteries as well as inspected the cables. And still that starboard engine cranks slower than the port; albeit, it's all a bit better, actually both engines crank better. So, it ends up the positive and negative cables on the starboard motor are about ten feet longer than the port motor; that voltage drop is enough to make a difference...… So, if I was to keep batteries for starting the boat I would probably double up that positive cable to the starboard starter but towards the end of the year I moving away from batteries to start the engines.
Click to expand...

Have to ask about moving away from batteries to start the boat. How will you start the boat without batteries?
 
hottoddie said:
I'm surprised to see group 31s being used on 450 Cummins but 3 of them should work if all 3 are in good condition and all the connections are also good. Check the cranking voltage at the starter with a digital volt meter and at the battery terminals. Have you checked the water levels in the batteries? I suspect you had the starboard batteriesz freeze over the winter and if so they are junk.
Click to expand...

I've never seen that either on a boat of your size. I would have expected you'd have 8D's. I wonder if the previous owner swapped them out and went to the group 31's.
 
FootballFan said:
Have to ask about moving away from batteries to start the boat. How will you start the boat without batteries?
Click to expand...
using ultracapacitors - specifically Maxwell Starting Modules. They are the size of a single Group 31 battery but have greater cranking capacity than 8D batteries and are good for over a million start cycles.
Before Sea Ray stopped yacht production they were working towards engine starting using this technology and the batteries proper were to be solely dedicated for house loads.
 
Last edited:
Very interesting.

Knowing at a distance a little bit about what you do when not boating - I know this is well thought out.

Is this start only? Will they power the thruster(s) and anchor windlass also?

Sorry if I am hijacking thread. Just learning something new and has my interest peaked.
 
Our dock neighbor has QSM-11s that the starters were slow. He replaced 1, and it made all the difference, so he replaced the other. Now all is good
 
swaterhouse said:
Larry do you know the CCA or MCA rating on the new batteries?

The previous owner replaced the port batteries on my boat before I surveyed, I replaced the starboard right after I purchased. My port always cranked slower than starboard (but not so slow as to cause concern). Didn't think all that much of it until this year when I replaced all my batteries and started looking at CCA/MCA ratings. My port batteries were right at minimum specs, my starboard batteries were 50% greater.

Looks like the 450C needs 1250 CCA or 1560 MCA, so your batteries need to be at least half that rating.

Either way sounds like your worse off this year so its either bad connection, bad battery or bad starter (unlikely).
Click to expand...


Update:
Tested for voltage drop at Stbd side solenoid in engine room (inside the big black box on fire wall), found voltage droped at the solenoid on both sides, this indicates to me that there is a bad connection before the solenoid. I ran a test cable (3/0) from batteries to the solenoid (primary), motor starts! Still need parallel switch to start (this is how they both were last year) but at least she starts. Will be working on routing new positive cable from battery bank to solenoid
 
Larry said:
Update:
Tested for voltage drop at Stbd side solenoid in engine room (inside the big black box on fire wall), found voltage droped at the solenoid on both sides, this indicates to me that there is a bad connection before the solenoid. I ran a test cable (3/0) from batteries to the solenoid (primary), motor starts! Still need parallel switch to start (this is how they both were last year) but at least she starts. Will be working on routing new positive cable from battery bank to solenoid
Click to expand...
Larry - first try and move the battery cable from the solenoid interface stud on the box to the engine starter cable stud (the other side of the solenoid) on the box and completely bypass the solenoid and see what happens. In my case I had thought someone cycled the solenoid when cranking the engine and damaged it.
 
Larry said:
Update:
Tested for voltage drop at Stbd side solenoid in engine room (inside the big black box on fire wall), found voltage droped at the solenoid on both sides, this indicates to me that there is a bad connection before the solenoid. I ran a test cable (3/0) from batteries to the solenoid (primary), motor starts! Still need parallel switch to start (this is how they both were last year) but at least she starts. Will be working on routing new positive cable from battery bank to solenoid
Click to expand...

This is a fairly common problem with cables and connections. Make sure the lugs/terminals on the ends of your cables are clean and tight.
 
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