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Old 04-22-2021, 08:33 AM   #1
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Starting a diesel

Hi,
We have a relatively new to me Nordic tugs 37 with a cummins 6BTA and I know that you should not crank the starter for very long so that water doesn't back up into the turbocharger and cylinders. My question is what is too long and how long do you have to wait after before reattempting? A secondary question would be the same thing for the generator. The gen actually can be a little stubborn to start and I will be addressing that in the next while.

Thanks ahaid of time,

Jim
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Old 04-22-2021, 08:35 AM   #2
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How long is too long really depends on the exhaust system design. On my generator, for example, I can crank as long as I want without flooding it. Even with a water lift muffler, the geometry is such that it'll push water out the exhaust while cranking, so the muffler doesn't over-fill and lead to flooding. I don't know if that's the case for my engines, but in 35 years, nobody has ever flooded them from too much cranking.


If the system is prone to filling up while cranking, it's not just a "wait before trying again", you'd need a way to drain the water out of the muffler before the next attempt.
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Old 04-22-2021, 08:38 AM   #3
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I would suggest asking your question of the boat's manufacturer. The answer might even be in the owner's manual, but you should be able to call or email them.
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Old 04-22-2021, 08:44 AM   #4
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I would suggest asking your question of the boat's manufacturer. The answer might even be in the owner's manual, but you should be able to call or email them.
Good suggestion. Please correct me if I am wrong! Only they can answer that because they know the engine and muffler setup. Yes?
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Old 04-22-2021, 09:02 AM   #5
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Well, either the manufacturer or a legit mechanic who can inspect the system and look at the rise in the exhaust, etc, and help you estimate the risk, teach you to drain it, and advise you how it can be retrofitted to make it easier for you to drain when needed.
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Old 04-22-2021, 09:34 AM   #6
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Should not really need to worry about it unless something is wrong.

A healthy diesel should start within a few revolutions, and this is a non-issue. If it does not start, like from air loading or whatever, just go close the sea cock before cranking it a lot. Then DO remember to reopen it once it starts!!

It all depends on how the exhaust is laid out, the various elevations. If highest point of the muffler outlet is higher than the mixing elbow, you need to be careful. If mixing elbow is the highest part of the exhaust system, no worries at all.
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Old 04-22-2021, 04:47 PM   #7
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If you're going to maintenance that requires a lot of cranking, shut the seacock.
A diesel needs 3 things to start. Fuel, compression, and enough heat generated in the cylinders to auto ignite the fuel. That means the rings/cylinders have to have enough compression to raise the internal temps to above 500F. As air is compressed, the temperature rises. In really cold weather, you may need to use a block/pan warmer, or preheat the incoming air with a hair dryer.
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Old 04-22-2021, 04:51 PM   #8
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We don’t have water lift mufflers on our mains so the water drains right out instead of backing up into the engine. So it depends on your muffler.
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Old 04-22-2021, 06:13 PM   #9
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Ski's answer is exactly dead on. You're asking the wrong question. Also what kind of generator do you have? Many require you to hold the start button even after it has started. Many have a preheat function that is on the bottom side of the rocker switch.

Your 6BTA should fire right up unless you are in a really cold area. They do have intake gride heaters. Some don't like them but I do believe they help when working properly. You can turn the "ignition" on and let it sit for a bit with the alarms blaring. You will note a significant draw on the ammeter indicating the grid heater has activated. My current CTAs actually have a light that comes on when the heaters activate so it all depends on the panel setup. Let it warm for a little bit. It really isn't like glow plugs but it will help a bit to warm the intake air and will help a bit in starting.

Also, an issue I had on one of my 6BTAs was that there was not enough current reaching the start stop solenoid so it was slow to open. I thought I was having serious compression issues. But it was totally random and inconsistent and would even happen on a warm engine. So you may want to check that if the symptoms are "irregular". If so, all I did was clean the connections on everything related to that and never had an issue again. Fired right up. Dead of summer?....immediately at starter engagement. Completely cold soaked in dead of (Texas) winter, 3 seconds cranking max....and smokey as hell.
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Old 04-22-2021, 08:39 PM   #10
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My John Deere starts instantly if it receives fuel. I always fuel-prime the engine if not used recently.
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Old 04-23-2021, 02:07 AM   #11
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My waterlift muffler is below the waterline so I could easily fill it and the cylinders with constant cranking. I disconnect the water hose at the exhaust elbow and spill it into the bilge if I have a problem. If I close the seacock and it starts the impeller disintegrates. Not doing that again.

The wait between attempts is to allow the starter to cool off and not overheat. If your engine hasn't started coughing after three 5 second attempts you might want to bleed the secondary.
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Old 04-23-2021, 10:41 AM   #12
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I would like to thank all of you for your reply.

I called Nordic tugs as suggested in one of the posts and they said that it is BS that there exhaust will fill with too much water if cranked for a long time. Maybe others would have a problem. It kind of makes sense because the air coming out of the engine along with the water should push out the water already in the exhaust.

The mention of the startup procedure for the generator is also well taken. I will be studying the manual for it to make sure I'm starting it properly.

Thanks again
Jim
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Old 04-24-2021, 06:42 AM   #13
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"I called Nordic tugs as suggested in one of the posts and they said that it is BS that there exhaust will fill with too much water if cranked for a long time. Maybe others would have a problem. It kind of makes sense because the air coming out of the engine along with the water should push out the water already in the exhaust."

Call again , speak to a different expert.

The combustion of the fuel heats and expands the air and fuel in the cylinder , which is the source of the energy required to lift water from the lift muffler into the exhaust pipe .

Folks would no be offering advice about lift mufflers unless there was bad experience with their operation.
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Old 04-24-2021, 08:03 AM   #14
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"I called Nordic tugs as suggested in one of the posts and they said that it is BS that there exhaust will fill with too much water if cranked for a long time. Maybe others would have a problem. It kind of makes sense because the air coming out of the engine along with the water should push out the water already in the exhaust."

Call again , speak to a different expert.

The combustion of the fuel heats and expands the air and fuel in the cylinder , which is the source of the energy required to lift water from the lift muffler into the exhaust pipe .

Folks would no be offering advice about lift mufflers unless there was bad experience with their operation.

It all depends on the system layout and as a result, how much force it takes to push the water up over the top. In some cases (like my generator), the airflow from cranking is enough to do it and avoid the muffler filling up. In other cases, you won't get water all the way through until the engine actually starts and exhaust gas volume increases.
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Old 04-24-2021, 08:24 AM   #15
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NL gen-set has a limit of 60 seconds. After that, the water in the muffler will back up and you will be sorry.

But as ski said, if it takes 60 seconds, you have other problems.
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Old 04-24-2021, 09:17 AM   #16
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Hi Jim,
I recently sold my NT 37 with Cummins 6BTA. They are, in my opinion, great boats with great engines. Ski gave you a good answer. The info I remember is generally don't crank longer than 60 seconds. Both my generator (Onan) and engine always started within a few seconds. I installed an oil pan heater (250 watts) on the Cummins, and except when at anchor leave it plugged in. This makes for easy starts and keeps the smoke at startup way down.
The air preheat system can be an issue. On many boats, the system stops working (no actual preheat) because the magnetic switches can overheat and fail, connections can work loose overtime, etc. Also, this heat system is designed to operate in an "off and on" manner until the engine reaches either a set rpm or temperature (as a "pollution control" measure). When cycled on, the draw can put a huge load on your alternator which can be problematic especially if operating other high draw items at the same time (like bow thruster or anchor windlass). This system operates "automatically". So I installed a control switch so I could "shut off" the air preheater after the engine started.

For starting, turn on the key and watch your voltage guage on the dash. It will dip down quite low. Wait for the needle to "jump" to the right indicating that the preheat just shut off, and then push the start button. The engine should fire in a couple of seconds.
If your generator has glow plugs like mine did (Onan), push the start button and hold it down until the engine starts. The starter will not engage until the glow cycle is complete and the engine should start within a few seconds of the starter engaging.

For much more info on your Cummins engine check our Tony Athens' website for his business Seaboard Marine in California. He is a well respected diesel expert and freely shares lots of information under "Tony's Tips" and in the various "forums" on his site. sbmar.com
Hope that helps. PM me if you have any specific questions.
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Old 04-24-2021, 11:58 AM   #17
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What FF is trying to say is just because they are from Nordic Tug and answers the phone does not make them an expert. Especially if their tone was “that doesn’t happen on our boats”. It’s a very common “issue”. One most boats can suffer given the wrong circumstances. I don’t care who told me what. I would never indiscriminately crank my engine for long periods of time without addressing this issue. Obviously there are other issues to be addressed if you have this issue.
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Old 04-24-2021, 01:24 PM   #18
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I have two NL 8kw units with glow plugs. They start easily with a cold engine with 15 seconds of preheat before cranking. If you don't pre heat it takes lots of cranking. Check if you have glow plugs to see if they are operational.

On the cummings use the grid heater for about 15 seconds and they keep it on while cranking if you can. Stop after about 10 seconds max and let the heat soaking the pistons and surrounding walls and repeat the process after about 30 seconds waiting. Check to see if the grid heater is functional.

Flooding as noted in the past posts is design dependent on the installation.
My old volvo MD11 was slow to start in the winter. It took about 15 seconds of cranking then you waited about 30 seconds and then would start on the second cranking. It had about a 17 to 1 compression ratio and needed the extra to get it going. No grid heater or glow plugs. It would start immediately with some warmth in the block. Key if you have a grid heater or glow plugs use them for a preheat if the engine is cold. The NL generators start best when using the glow plugs for each start.
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Old 04-24-2021, 01:27 PM   #19
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it should start after 1 turn unless in arctic, then use preheat.
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Fix the engine starting problems, not the effects.
Apologies to be abrupt but its better to be abrupt than confused by BS.
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Old 04-25-2021, 06:52 AM   #20
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"I have two NL 8kw units with glow plugs. They start easily with a cold engine with 15 seconds of preheat before cranking. If you don't pre heat it takes lots of cranking. Check if you have glow plugs to see if they are operational."


This is common on engines fitted with pre combustion chambers.
The combustion pressure in the chamber seldom gets hot enough to fire the fuel , so starting assistance is needed almost 100% of the time.


Either a preheat glow plug or a tiny squirt of ether does the job.
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