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 From there, when the piston comes down and tries to compress the "air" that has been replaced by water...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.Can someone explain why shutting off the raw water intake while cranking is important, is this something that applies just to this motor.
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the starter turning fills the cylinders.From there, when the piston comes down and tries to compress the "air" that has been replaced by water...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.
the trick is trying to make the first place you look the last place too.Good call Les. It is usually the last place you look. I find that true for keys.
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.PS: My Ford Expedition doesn't have a radiator shut off valve either.
It was a bit of "tongue in cheek" about my gasoline engine radiator.fundamental differences between diesel and gasoline
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.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.
Why?
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.
Jim...
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.
Perhaps on other boat designs, but not on mine.The air will have time to bubble out of the muffler without expelling the water.