Interesting.
I had mine hydro-lock last weekend and come to think of it - my outdrive was up 3/4 of the way, too...
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| Author: | soggydawg [ Fri Dec 05, 2014 10:41 am ] |
| Post subject: | hydra lock |
I have a 4winns vista 268 with a Volvo penta 5.7 l Gs engine and a Volvo penta smtd dual prop outdrive. I have had this boat 4 years. I have experienced hydra lock on the engine twice. The 1st time I did not know why the engine would not start as it would not turn over and then the starter gear broke a cog off the ring gear on the flywheel. Got towed back to the marina where I learned all about hydra lock which is simply water that has come up through the exhaust pipes to the top of the pistons. Engine had to be pulled and the starter rebuilt and the flywheel ring gear replaced. Total bill $ 6000. THat was in year one. Happened again in year 4 but I was able to start by pulling the plugs, turning the engine over, to pump the water out, and then replace the plugs . In each instance I was front and rear anchored with the stern into shore , outdrive up and in shallow water. In both instances the wake from larger boats would rock my boat up and down . Volvo penta told me that they stopped installing exhaust flappers in the year 2000 and elongated the manifolds up and installed 8 inch risers so water would have a harder time getting to the engine. They also cautioned boat manufacturers to install the engines so that there was at least 14 inches between the outside water level and the top of the risers at dead calm and level. I measure mine to be 15 inches. I have since been double anchoring the same way but have left the outdrive down and have not had the problem. Since my exhaust bellows is in good shape and is a clamped fit not a loose fit, I cannot figure out why water gets in when the outdrive is up. I like to raise the out drive when in shallow water to protect that dual prop. I understand that the rocking motion of the boat compresses the water between the boat and the bottom and can pump it up the exhaust but I don,t understand what difference the inclination of the out drive makes. Any body have any ideas ? |
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| Author: | LouC [ Fri Dec 05, 2014 1:42 pm ] |
| Post subject: | Re: hydra lock |
1) given the problems you have had, I would not anchor from the stern, because it can pull the stern down and if you get waves against the stern that makes it easier for water to get up the exhaust 2) I disagree with Volvo removing the flappers, in some installations this may be OK but obviously not in others. 3) You need to have the static water level measured in that boat and it may need riser extensions. I have the OMC one piece manifold/riser unit and I wish they were still made. No gasket to leak and the engine has never sucked up water. Most important is to get your static water level measured. |
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| Author: | deafwish [ Fri Dec 05, 2014 4:50 pm ] |
| Post subject: | Re: hydra lock |
Interesting. I had mine hydro-lock last weekend and come to think of it - my outdrive was up 3/4 of the way, too...
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| Author: | Graham R [ Fri Dec 05, 2014 4:51 pm ] |
| Post subject: | Re: hydra lock |
LouC wrote: 1) given the problems you have had, I would not anchor from the stern, because it can pull the stern down and if you get waves against the stern that makes it easier for water to get up the exhaust 2) I disagree with Volvo removing the flappers, in some installations this may be OK but obviously not in others. 3) You need to have the static water level measured in that boat and it may need riser extensions. I have the OMC one piece manifold/riser unit and I wish they were still made. No gasket to leak and the engine has never sucked up water. Most important is to get your static water level measured. VP sell special "high" risers, they add something like 4" to the height of the risers above the water line I believe. I also vaguely remember coming across a spacer kit ; hasically it fitted in between the riser and manifold, to give that extra height. I can well imagine that a boat fitted with the OEM MHP drive shield st up, or a retro- fitted standard one with the stub exhauset rubber hose could suffer from water ingress if the drive was 3/4 up. It's basically on open ended tube, clamped at the shield end only but wide open once the drive is tilted. |
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| Author: | alex8q4 [ Fri Dec 05, 2014 8:47 pm ] |
| Post subject: | Re: hydra lock |
I am new to Volvo this year. One of the first things i noticed is how high the drive tilts compared to the Merc's. Does any one know what the height difference is between the the exhaust outlet on the end of the out drive, and the top of the exhause raisers when the drive is all the way up? I could be off base here, I cant remember for sure how my setup looks. I recall my drive will come up almost to the underside of the swim platform, and there is a few inches of clearance between the top of the exhaust raisers and the underside on the deck. In my mind the height of the two can't be too far apart. If they are that close I can see how water could back wash to the engine. |
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| Author: | acguy [ Fri Dec 05, 2014 9:12 pm ] |
| Post subject: | Re: hydra lock |
I not sure but from what I am reading, is your exhaust bellows the type the is only clamped onto the transome housing and then it is a slip fit onto the drive itself? If that's the case then I can see quite easily how water would ingress with the drive tilted up. I had that style when I first purchased my boat but switch it out to the style that attaches to the outdrive via the inside circlip and gear clamp |
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| Author: | fi.na.tine [ Sat Dec 06, 2014 2:07 pm ] |
| Post subject: | Re: hydra lock |
So just approaching this from a different angle as to prevention. Maybe getting a set of muffs with a plug screwed into the hose inlet and placing those over the intakes when anchored would prevent this. (I may be approaching it all wrong - I'm no rocket surgeon when it comes to engines.)If I am dead wrong, and this will never work, please let me know. You would have to take the muffs off when you wanted to go again, but seeing as though I anchor the same on the river, I would be interested to find out.... |
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| Author: | LouC [ Sat Dec 06, 2014 2:13 pm ] |
| Post subject: | Re: hydra lock |
The water that's causing a problem, is going up the exhaust, not the water intakes on the drive.... This is not a problem usually when the engine is running because the pressure of the exhaust gases push the water out, unless the engine backfires or diesels and runs backward for a second which will pull water up the exhaust. Its a problem with the engine off, if the stern sits low in the water and waves are pushing against the stern. Like I said, since Merc has always used flappers, I question Volvo's assertion that the flappers in the Y pipe are not needed. If the exhaust risers are WELL above the static water line that might be so, but that is not so in all installations. In fact I bet that the static water line is rarely if ever measured unless the boat was having a problem. So the flappers in the Y pipe assuming they were functional is a fail safe set up.... I read Volvo's service bulletin on this. They said that the flappers were not effective and would fail and block the exhaust. This is wrong in my experience in that: The Volvos in question were the joint venture models similar to the OMC Cobras of the same era. 1) My OMC with flappers never pulled back water. 2) the only way these flappers can fail is if you have a bad overheat. The lack of cooling water will melt them. So you remove the risers and replace them if you have an overheat. |
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| Author: | fi.na.tine [ Sat Dec 06, 2014 3:05 pm ] |
| Post subject: | Re: hydra lock |
I knew there had to be a failure in my logic. |
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| Author: | deafwish [ Sat Dec 06, 2014 11:21 pm ] |
| Post subject: | Re: hydra lock |
LouC, How plausible is it for an engine to ingest water on a startup backfire while on ear muffs (out of the water) by vacuuming the water already in the manifolds? There's a good few litres of water in them and they're much closer to the cylinders than the flappers! I'm thinking this is very plausible and would make the flappers redundant even when the boat is in the water...
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| Author: | fi.na.tine [ Sun Dec 07, 2014 1:36 am ] |
| Post subject: | Re: hydra lock |
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| Author: | LouC [ Sun Dec 07, 2014 3:03 am ] |
| Post subject: | Re: hydra lock |
It can happen either way. The engine diesels and sucks in its own water. The operator slows down too fast and the following wave goes up the exhaust. Volvos faulty logic is shown in that most boats with thru the transom exhaust have flappers too. Why would Merc the biggest maker of sterndrives in the world, not save money by leaving them off if they thought they could? They disagree with Volvo too. Honestly if I had a Volvo unit that the OMC parts would fit, I'd install them no matter what Volvo says. All of the models in this range are way out of warrentee anyway so it doesn't matter what Volvo said back in 2000. Look at any Merc sterndrive made in the last 50 years they all have them. As I said in an earlier post, every installation is different. Many boats are marginal on the static water level measurement. Many marine mechanics don't even understand this or know how to measure it. But its critically important. In fact here you go, I just remembered this. As I said, I never had a hydrolock problem on my '88 OMC. However, when I had that overheat back in July '13 here's what happened: the raw water hose popped off the P/S cooler on the rear of the engine. The impeller continued to pump seawater in the bilge, weighing down the stern a LOT. Then engine overheated. Three factors: Flappers vaporized Stern low in the water Engine stalled after overheating When I checked the plugs and compression (which by the way, was about the same as 3 years before that, lucky) there was no sign of water in the cylinders, but the plugs did have a bit of rust on them, so some small quantity of salt water did get sucked up. Replaced the plugs and all was well. No water in the oil. Put in new flappers. This engine has enough static water level that this did not cause it to hydrolock. Deaf, as low as your boat sits in the water, I'd think more about it. Ask the guys at Hy Tek Marine exhaust. Do they think you need them based on how your boat sits? I also think the specific design of the riser section of the exhaust affects this issue, it was proven by Merc in their tests and they changed things because of it. http://www.marinemechanic.com/merc/dist ... engine.PDF |
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| Author: | alex8q4 [ Sun Dec 07, 2014 11:30 am ] |
| Post subject: | Re: hydra lock |
That was a very interesting read Lou! Did you happen to come across the document that shows how to measure static water level? |
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| Author: | LouC [ Sun Dec 07, 2014 11:49 am ] |
| Post subject: | Re: hydra lock |
I had seen it, but couldn't find it this time. It is out there though...something about using a clear tube to see how high the water level would be inside the boat relative to the top of the riser. |
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| Author: | rpengr [ Sun Dec 07, 2014 1:14 pm ] |
| Post subject: | Re: hydra lock |
deafwish wrote: LouC, How plausible is it for an engine to ingest water on a startup backfire while on ear muffs (out of the water) by vacuuming the water already in the manifolds? There's a good few litres of water in them and they're much closer to the cylinders than the flappers! I'm thinking this is very plausible and would make the flappers redundant even when the boat is in the water... I don't think it is plausible to suck in enough water to hydrolock an engine while running on the muffs (assuming the drive is down and water is draining out the prop normally). If the engine were to backfire or diesel in reverse while on the muffs, it could suck in a some drops of water that is coming out the tail of the riser, but were talking droplets, not a cup or so that would be required to hydrolock. That's my opinion for what it's worth. I would like to add two other optional parts into this conversation: 1. Some engines have valves on the risers that let air into the exhaust chamber if a suction is created (by wave action, changing temperature, or reverse rotation from backfire or similar). I have these valves on my 2000 VP 5.7GSPWTR as shown in this picture (on the inboard side if the risers, with a hose going towards the carb.) I have called these "anti-siphon valves", although I cannot find what the name is for sure.  2. Most exhaust bellows I have seen are slotted along the bottom folds to let water drain freely out the bottom of the bellows (especially with the engine trimmed way up. Do those of you who have had hydrolock problems have these slots in you exhaust bellows? I suggest that the slotted bellows are better than the non-slotted version. Ray |
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