PDA

View Full Version : sea water in cylinder from exhaust, how to avoid repeat...



bikedaft
29-09-10, 06:50
hi, 3gm30f yanmar sea water cooled, cooling water enters exhaust at elbow about 12" beneath waterline. the exhaust then dips about 6" to a vetus waterlock, then exhaust runs about 10feet up to transom. there is a high loop just before transom about 12" above hul opening. there is no seacock on transom exhaust port.

twice have tried to start engine after a storm where the boat has been bouncing about, to find it would turn over half a turn then stop dead. first time thought was duff battery and got it going by using decompression levers and started one cylinder at a time, 2nd time realised what had happened, and started it same way. engine seems fine, no bent con rods, compression fine (phew!)

main problem (i think) is that there will always be some water in the loop immediately after engine elbow, before vetus waterlock. compounded by the antisyphon loop emptying itself into the same bit of exhaust hose when engine stops. can't make the waterlock lower, hull gets in the way. could fit a valve in exhaust immediately after engine, but would be hard to stabilise it while opening/shutting it, and dissimilar metals etc (s/s exhaust elbow).

have taken exhaust hose off exhaust elbow as short term measure. have drained vetus waterlock and will see if any water getting into it from stern when next visit. fairly easy to fit seacock on transom, but don't think thats the main problem.

i could make exhaust hose rise up high immediately after engine? but then what do i do about the antisyphon device on the cooling water that's fitted after the engine (and enters at elbow)

hope this is making some sense, thanks for reading so far. :-)

earlybird
29-09-10, 08:05
Can a high-rise exhaust elbow be fitted? This would eliminate the loop before the waterlock, which seems to be the reason for your problem. The antisyphon device would discharge into the new elbow.
I think you've been lucky not to damage the engine so far!

30boat
29-09-10, 09:05
What type of anti siphon device do you have?Is it one of those with valves in them?These tend to stick with salt and become useless.The valveless ones are much more reliable.

Juggler7823
29-09-10, 09:07
Have you cranked the engine over for a long time with the cooling water turned on. Don't know about yanmars but VP 200x series was always prone to sucking water from the exhaust hose into cylinder during difficult starting with inlet seacockon.

rob2
29-09-10, 09:12
It rather sounds as though the water lock doesn't have sufficient reserve capacity to hold all the water present in the system when the engine stops. Check out the recommendations in the Vetus catalogue and calculate the internal volumes. Do not raise the exhaust between the engine and water seperator! One other thing - are you sure the anti-syphon valve is working? Just try blowing into it with the engine stopped, it should allow this. Sucking should cause it to close...

Rob.

Tranona
29-09-10, 09:19
You have identified the key problem. There is not enough fall to the waterlock - Vetus recommend 30cm and you only have half that. Possible solutions are to fit the Yanmar high rise manifold or one of the newer type horizontal waterlock/silencers from either Vetus or Halyard. However, I suspect the shape of the hull will limit their use. Details in the latest Vetus catalogue p61 or on the Halyard website.

bikedaft
29-09-10, 09:25
earlybird - yes i think that this is what i have to do, i can't see any other way of doing it properly.

30boat, i don't think the vetus ones have a valve in them?

juggler 7823, no its after the boats been left a while. also the compression is sufficient to push the coolant out the exhaust at stern even just on cranking.

rob2, i think the problem is the section of exhaust between engine and waterlock (tho the waterlock could also be insufficient!)

if i raise the exhaust immediatley after engine it will have to be of s/s, and will run hot as the cooling water cannot be added until after the exhaust is descending again. and there really is no space to do it other than go sideways into a cockpit locker...

thanks for the replies

noelex
29-09-10, 10:35
I think you are the right track to fix the problem.
However, one other source of the water, at least on some engines, is from corrosion inside the mixing elbow. When the boat is pitching is also when this causes a problem. Water can enter the last cylinder from this route.
I doubt its the cause, but check.
Water in the engine is very bad and your temporary steps of removing the exhaust hose would not fix the problem if it is water entering from the elbow.

Bilgediver
29-09-10, 11:37
h
i could make exhaust hose rise up high immediately after engine? but then what do i do about the antisyphon device on the cooling water that's fitted after the engine (and enters at elbow)

hope this is making some sense, thanks for reading so far. :-)


Yes it will be interesting to see if water flows into the system when the boat is at rest as you are doing. This is a frequent problem in boats with low lying engines and either no anti syphon or one which is faulty as in these cases water can syphon into the exhaust through the water pump if the sea cock is left open.

My first suggestion if you go sailing before this is fixed is that you evacuate all water from the exhaust before stopping the engine IE close the sea cock 20 seconds before stopping the engine. A short burst will blow the water out.
If your anti syphon is working then you can then leave the sea cock open ready for the next start.

Your problem could be that the water lock is too small for the hose length/ volume and one way to employ a larger water lock and avoid the uphill rise from the exhaust elbow is as others have said fit a High Rise exhaust elbow. This is a common feature and further reduces the chance of back flow and often needed where a small engine such as Beta is installed instead of an old Volvo MD rock crusher. I believe Yanmar can supply one. Then make sure your water lock can accept the volume of water from the exhaust hose.


If you have a problem with water volume can you re run a shorter hose from the water lock to a side outlet? You say that your exhaust hose rises to 12" above the outlet but you do not say how high the outlet is above the waterline! Is the hose level rising well above the level the sea reaches when your boat pitches in a seaway??? Might have to take this loop to almost deck level.

It might be worth speaking to Vetus about fitting a second waterlock in the event there is not room for a bigger one close to the engine though this might increase back pressure slightly.

TamarMike
29-09-10, 12:16
Do you worry about a small amount of seawater in your bilge? You could fit a valve to the drain on the water box and leave it open when the engine is not running (I did that on my previous boat in conjunction with a gate valve at the transom as it had no swan neck).

bikedaft
29-09-10, 12:54
tranona, will check with vetus.

noelex, good point, but its fine. i check this about 6 monthly. apparently the yanmar ones do fail semi irregularly.

bilge diver/tranona - will get measurements for a yanmar high rise exhaust elbow, but don't think there is space for this under cockpit sole. the exhaust hull outlet is 6" above w/l, tho probably underwater above 4-5 knots... (overhanging stern). it sounds as tho the high rise exhaust elbow should have been fitted 10 years ago at installation, but wasn't due to space? will running the engine without cooling water thru it not trash the impellor? ok better than replacing piston liners/compression rings etc!

tamarmike - think that's what i am going to do short term. easy to fit hose from drain of waterlock, with a valve on end of it, lift up with piece of string to open/shut it, and then return to bilge. it takes 5-10mins to drain waterlock as its a small dia drain. then pump bilges.

i got a pm from someone who had the same problem, it turned out to be his water cooled stern gland, thanks, but we are not that advanced, its an old grease stuffing box. :-)

thanks to everyone for your helpful replies.

bikedaft
01-10-10, 19:23
been thinking again (ok i'll stop soon!)

do i really need the anti siphon loop in engine sea water system between engine and exhaust elbow? there is effectively already one on the inlet side, a coarse filter, just above the sea water inlet seacock, well above waterline. the sea water bubbles up thru a pipe, then falls down thru a coarse filter. so when suction from impellor ceases, the water drains back down to sea level in seacock pipe. so if i got rid of the antisyphon loop at outlet side of engine it would reduce amount of water in this problematic part of the exhaust before the vetus waterlock, after engine shut off.

or instead of running impellor dry, fit a 3 way tap to sea water hose after engine, before it enters exhaust elbow, and dry out the exhaust before stopping engine. been doing this for 37 years on dad's sabb engine. as long as vetus waterlock is sufficient, but will be testing this...

earlybird
01-10-10, 19:32
You say in your OP that the mixer elbow is 12" below the water-line. In that case, an anti-syphon device is absolutely essential. The filter won't do that job.
The tap idea might work up until the day you forget it!

bikedaft
01-10-10, 19:40
ok, but there is a vetus waterlock in the exhaust between exhaust elbow, and transom. if water routinely came down this way the engine woud have died a long time ago, the anti syphon loop is only for the cooling water, not the exhaust hose itself?

the main problem is that after shut off there is not enough drop between exhaust elbow and top of water in waterlock. certainly less than recommended tho.

noelex
01-10-10, 19:45
been thinking again (ok i'll stop soon!)

do i really need the anti siphon loop in engine sea water system between engine and exhaust elbow? there is effectively already one on the inlet side, a coarse filter, just above the sea water inlet seacock, well above waterline. the sea water bubbles up thru a pipe, then falls down thru a coarse filter. so when suction from impellor ceases, the water drains back down to sea level in seacock pipe.

You need to let air into the system when the engine stops. If you don’t the water would not drain from the coarse filter even when it is above the waterline.
I think you will find without the anti siphon loop water would stay in the inlet pipe

Courageous
01-10-10, 20:08
I thought 3gm30f was fresh water cooled? Isn't that what the "f" stands for at the end?

noelex
01-10-10, 20:17
I thought 3gm30f was fresh water cooled? Isn't that what the "f" stands for at the end?

In a freshwater cooled engine seawater is still used to cool the freshwater inside the engine. The seawater exits via the exhaust and can enter the cylinders from here.
It’s a rare problem, but serious when it occurs, with a risk of destroying the engine.

earlybird
01-10-10, 20:27
ok, but there is a vetus waterlock in the exhaust between exhaust elbow, and transom. if water routinely came down this way the engine woud have died a long time ago, the anti syphon loop is only for the cooling water, not the exhaust hose itself?

the main problem is that after shut off there is not enough drop between exhaust elbow and top of water in waterlock. certainly less than recommended tho.

Yes, the waterlock catches the water that runs back from the exhaust pipe after shutdown, but that's not the point. The pipe between the cooling water intake and the mixer elbow will be full of water, with the exit below the water-line. This will form a syphon past the pump, and, in time will fill the whole exhaust system, and the engine, up to level of the water-line.
The reason that you are now seeing water run back from the filter is because the anti-syphon device is letting in air to allow this.
However, I read your original problem as being residual water in the exhaust between the elbow and the water-lock being splashed into the exhaust manifold by boat movement. This can be cured by avoiding the loop that you seem to have in this pipe-run. But the anti-syphon device is still essential in the cooling water line.

Courageous
01-10-10, 20:35
Quite right Noelex - the OP stated at the beginning though "hi, 3gm30f yanmar sea water cooled" which immediately took me down the seawater cooled route........

The words need to be correct to make sense no?

noelex
01-10-10, 20:49
Quite right Noelex - the OP stated at the beginning though "hi, 3gm30f yanmar sea water cooled" which immediately took me down the seawater cooled route........

The words need to be correct to make sense no?

Yes agreed it was confusing terminology that I missed in the OP
I understand now.
Hopefully my basic explanation was still useful to some people.

Courageous
01-10-10, 21:14
Sure it will be. Thanx for picking up on it though.

bikedaft
01-10-10, 22:00
You need to let air into the system when the engine stops. If you donít the water would not drain from the coarse filter even when it is above the waterline.
I think you will find without the anti siphon loop water would stay in the inlet pipe

think that's the nail in the coffin of one idea.

thanks for the replies folks.

will fit a sea cock to the transom exhaust outlet, and drain the exhaust somehow whether intermittently with bits of hose from waterlock, or by drying exhaust with "T" valve in sea water outlet side somewhere

cheers!