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Old 30-07-2010, 09:23   #1
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Question Perkins Engine - Raw Water in Crankcase

Trying to help a friend of mine solve an engine flooding problem (water in the crankcase). This is what we have looked at to date:
1. There is an anti-siphon loop in place - top of loop is 34" above waterline. Checked the siphon and it works properly.
2. Exhaust loop is at the same height, 34" above waterline, exhaust thruhull is above waterline.
3. The heat exchanger / exhaust manifold are both slightly lower (~3-4") than waterline.
4. Muffler is 60" below top of the exhaust loop (i.e. ~26" below the exhaust manifold).
5. Coolant level is ok - we know for sure its salt water in the crankcase.
6. Engine is 20+ years old - this is something that has happened only within the last couple of years. He was unable to figure out why water was coming in so he has installed a gate valve on the exhaust (~16" below waterline). He has to close the gate valve and raw water after shutting the engine down to prevent water coming in). This last time, they had an issue and forgot to close the valves which stayed open overnight - flooded the next morning.

The only thing I can think is the exhaust pipe is filling with water (or has a certain amount of water in it when the engine is shut down) and creating a pressure head in the exhaust manifold - this pressure head could potentially be up to ~38" (distance from manifold to top of the exhaust loop). So is the water leaking in through the exhaust valves? A diesel mechanic is suggesting he have new exhaust manifold (outlet) manufactured that includes a vertical loop going up before coming back down, connecting the siphon loop and then down to the muffler. Not sure if this will solve the problem?

If its not coming in from the exhaust then is is possible to come in from inside the heat exchanger - just wondering know if we should try pressure testing that? If there was a leak there this would be a continual problem - his issue only happens with engine off.
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Old 30-07-2010, 09:48   #2
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Mine has a loop from the maniflod that raises it about 12-14" above the water line. This keeps any water that is in the exhaust line from backing into the engine. You could also put a valve here to relive any back preassure after you shut down. 38" is alot, but not uncommon.

I think that you have water in the exhaust line that is giving you problems, I don't think you are sucking water from the outside.

If water was coming in from the heat exchanger you would see it in your coolant, not the crankcase.

Check you raw water pump, water could be getting pass your seal here, remote possibility.

I also close my through hull into the engine. It just removes any preassure from the front of the pump.

All this advice is worth what you paid for it, I could be full of crap.

Good luck, let us know.
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Old 30-07-2010, 09:55   #3
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This one has me stumped...You would/should be getting a hydraulic lock on the engine if it was comming through the exhaust valves and some serious rusting as quickly as over the week end it being salt water...

Water is not usually going to flow by your piston rings that easily and most will remain in the cylinder.

Are you getting any excess steam out the exhaust while running at normal temp?

If the inline exhaust valve cures the problem 100% all the time, then it dose point to that issue but this will be a new one on me as far as it ending up straight into the crankcase with out signs of hydraulic lock.

Re: your question on if it could becoming straight into the crankcase from the heat exchanger... my answer is no...as the only place it mates with the block is at the exhaust ports on the head...more common would be raw water/ coolent contamination in that case...I supose its possibal to have a crack in an exhaust port alowing water into the head and block but I would think you would have exccisive back pressure out the crank case breather if that was the case as well.

Plain raw sea water in the crankcase could come from several places if you were raw water cooled but is really isolated to down flooding as you summized already with a fresh watewr cooled system.

How does this engine Start?....and run?

Is there blue smoke?

Its possible to have say enough scoring/dammaged piston and rings on one cylinder or its wall to allow some water past the rings but we are talking rebuild ready condition here for that to be the case..blue smoke, oil consumption all that jazz...Water is less solvent then oil so it really doesn't seep past rings that readily.

Like I sad this one stumps me a bit from all my past experiences.

Engines are always teaching.... Im always learning..
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Old 30-07-2010, 10:07   #4
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I your raw water pump is gear driven check it out.

Do you have an oil cooler? If so that is a prime suspect.
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Old 30-07-2010, 16:04   #5
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I would suspect a siphon is being set up with the raw water valve. Then it's leaking by the raw water pump seal.
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Old 31-07-2010, 07:24   #6
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Originally Posted by never monday View Post
I would suspect a siphon is being set up with the raw water valve. Then it's leaking by the raw water pump seal.
Is this seal accessible from the impellor side or is this a big deal to replace?
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Old 31-07-2010, 07:46   #7
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Based on my Perkins (4-236) install, I would say that if it's water in the cylinders, that the volume of water in the exhaust hose when it is shut down is greater than the volume the water lift muffler will hold, so it backs up the exhaust manifold and into the cylinders through the exhaust valves. The loop in the exhaust hose should be near the engine so that most of the water runs downhill to the thruhull; alas, it is usually near the thruhull so it runs back to the engine. This assumes that you are confident the vented loop is working properly.

If it is in the crankcase/oil sump, I would agree with DeepFrz that the oil cooler is suspect. I doubt that a diesel that could get water in the sump from the cylinders via the rings, without noticing water in the cylinders or bending a rod, would have enough compression to start normally.

Good luck!
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Old 31-07-2010, 08:46   #8
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Only problem with that theory is the Oil cooler is in the fresh water loop on a fresh water cooled engine not the raw water loop.
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Old 31-07-2010, 09:48   #9
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are you needing to crank the engine much in starting it?? that can bring water into engine. friend had that happen repeatedly--his risers werent high enough. both are prime suspects. good luck.
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Old 31-07-2010, 11:35   #10
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Quote:
Originally Posted by DeepFrz View Post
I your raw water pump is gear driven check it out.

Do you have an oil cooler? If so that is a prime suspect.
I'll place a bet on the seals of the raw water pump.

My first Perkins was a 4-107 and I now have a 4-108
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Old 31-07-2010, 11:36   #11
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Is this seal accessible from the impellor side or is this a big deal to replace?
The pump needs to be removed and the seals pressed in.
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Old 31-07-2010, 11:50   #12
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Is this seal accessible from the impellor side or is this a big deal to replace?
To address the 2nd part if it's a big deal....well, it's nothing money won't solve.

Depending on who you know, for me, a rebuild was about 80 bucks for the Sherwood. YMMV. A new pump, as I recall, was $360-80. Again, someone will always tell that you paid w-a-y too much.

If that's the source of the problem it is an easy fix. It just cost money.

If that is not the source of the problem, it will cost more money...but the good news is you have a new/rebuilt pump.
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Old 31-07-2010, 11:52   #13
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I'll place a bet on the seals of the raw water pump.

My first Perkins was a 4-107 and I now have a 4-108 .
The part that stumps me is he said it only happens if they forget to close the valve on the exhaust line....If it were the water pump seals ( gear driven pump only ) it would happen all the time.
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Old 31-07-2010, 12:08   #14
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The part that stumps me is he said it only happens if they forget to close the valve on the exhaust line....If it were the water pump seals ( gear driven pump only ) it would happen all the time.
I'm scratching my head as well, and this is where I start unfounded speculation.

When the exhaust gate is open without the engine running there is a static 3' (or whatever it comes out to be) water column just wanting to slip by the pump seal. When the gate is closed (the 16" one) there is not the pressure from the water column exerted on the seal. (1- it's shorter; 2- the vacuum created by the closed value would limit the pressure.)

...but this brings up the question why is doesn't leak through the intake side.

So, I think this clearly means...I don't know.
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Old 31-07-2010, 12:19   #15
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The part that stumps me is he said it only happens if they forget to close the valve on the exhaust line....If it were the water pump seals ( gear driven pump only ) it would happen all the time.
read all of the original post

Quote:
He has to close the gate valve and raw water after shutting the engine down to prevent water coming in). This last time, they had an issue and forgot to close the valves which stayed open overnight - flooded the next morning.
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