Discussion in 'Ask All Sailors' started by John R, Feb 11, 2018.
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Sounds like a clogged fuel filter to me.
It's the exhaust that blows the raw water out of the muffler. If you crank with the raw water intake open and without the boat starting, then the raw water will build up in the muffler and ultimately back up through the exhaust hose into the manifold and from there into the engine's cylinders. From there, when the piston comes down and tries to compress the "air" that has been replaced by water... Well, as you know, air compresses but water doesn't. So you will basically destroy your engine.
That's why it says on my motor "Caution! Do not crank for over 30 seconds. etc."
So the point is that I'd been cranking for some time before, trying to start the engine so I was worried about the raw water backing up in the muffler. So, I had the raw water through hull closed while I fooled around with the engine. But if you aren't experiencing starting problems, then of course don't keep it closed.
It is called hydrolocking. It is really bad if the engine is running and water enters the cylinders, it is only bad if the starter turning fills the cylinders.
If the motor hydrolocks, the fix is to remove the injectors, close the water intake, and turn the engine over. If you are lucky nothing bad has happened and the engine will run again and all you need to do is replace the water pump impeller. If you are unlucky, the piston rods are bent and salt water is doing a job on your piston walls, and you need to replace your impeller.
Shutting off the raw water is intended to prevent over filling the water-lift muffler if it does not start right away.
I was having cranking problems an it turned out to be the starter selonoid push terminal to the key switch. I was almost going to pull the starter but decided to check one last thing.
Good call Les. It is usually the last place you look. I find that true for keys.
the trick is trying to make the first place you look the last place too.
I've never been able to pull that trick off, unless I don't really want to find it.
- Will (Dragonfly)
I would NEVER start my boat diesel without the raw water valved on.
At least on my boat, the Muffler/Quench system works the same way , engine running or starting up.
My sea water pump and the Diesel engine are...
Positive Displacement Pumps
Simply put, the volume pumping rates are constant at a given RPM.
1) Sea Water = Flex vane
2) Diesel = Pistons
My Diesel drives my Seawater pump. If your Seawater pump is not driven by your diesel, then I would be surprised.
Tip: Since I shut off most seacock when leaving the boat, I put my engine keys on the raw water seacock handle.
PS: My Ford Expedition doesn't have a radiator shut off valve either.
I'm not an engine guy, but I do know there are some fundamental differences between diesel and gasoline engines as well as cooling methods for engines mounted in automobiles and boats. James, your point sounds good, though. I especially like your method for storing your keys. That is just smart thinking.
- Will (Dragonfly)
It was a bit of "tongue in cheek" about my gasoline engine radiator.
The quickest way to burn up the rubber flex vane seawater impeller is Dry running.
At least on my boat, the seawater pump stays flooded, seacock open or shut.
When I change that rubber impeller, I bump my engine starter a few times to assure the seawater pump is flooded again.
PS: My Expedition water pump is Centrifugal type, but it is located at the lowest point on the cooling system and is engine belt driven, so it stays flooded all the time too.
Your right that the engine and water raw water pump are both positive displacement devices. The problem is that the exhaust system is designed so that fast moving exhaust air producing high pressure is required to push the water out of the muffler and up and over the loop in the exhaust hose. While cranking, there is not enough air pressure to expel the water. The air will have time to bubble out of the muffler without expelling the water.
Perhaps on other boat designs, but not on mine.
The diameter of the exhaust line and the exhaust port diameter is sized to prevent gas bypassing or bubbling through. Typically it is the exhaust port diameter that controls the exhaust system.
If those lines are too big and the seal loop too high, then it might be possible.
However, Hunter did a dang good hydraulic design.
I am still a bit worried about high seas and fore/aft wave action. If your engine is down and your seal loop has water, it can "slosh" back into the open valve on my engine, when the boat pitches forward.
My last estimate for my H430 is 8 foot seas. Higher than 8', I will start my engine. It is probably a good idea anyway to gave better wave control.
BTW the seawater volume flow rate is a pittance when compared to the exhaust gas flow volume.
PS: These systems are designed for and not guessed at.
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