Hydro Locked Mercruiser 5.0MPI Engine

Raft61 · **Posted:** Mon Jul 13, 2015 6:32 am

Sad story really (but could have been much worse...). As a result of some overheating problems I was having back in Jan (6mths ago), I nearly junked my engine...

While cruising around sightseeing recently, I put the engine into reverse and it started running rough. Not TOO bad but enough that the wife even commented that it didn't sound right. Headed back to the ramp and boat was a little hard to start when putting it on the trailer. Thought to myself that it's probably due for a service.

Tried to run it when I got home, but the engine just went "clunk" then wouldn't turn over anymore. Quickly checked the oil and it was a "chocolate milkshake" and over-filled to about 2/3rds to 1/2 way up the dip stick. Water in the oil!! Checked the oil filer and it was all through the top as well. No doubt I've got water in the cylinder and Hydro Locked the engine.

Thought it's probably due to a corroded manifold/riser, as the boat's about 10 yrs old and they have never been done (or even checked! Engine's in good cond and only done 240hrs) - In fact, at the last service I told the mechanic and he said he'd pull them out at the "next service" just to check them. As luck would have it that "next service" was due last month (just my luck to miss it by 1 month).

Also thought potentially maybe a head gasket (the usual suspect in a car) as I had three overheating incidents back in Jan until I found the cause (see http://www.smwebhead.com/phpBB3/viewtopic.php?f=11&t=13715 thread) - but I think the Merc has cast iron heads (not alloy), so hopefully not...

Quick ring around and the verbal diagnosis was the same everywhere. With that much water in the oil and Hydro Lock, engine likely to be trashed. No reconditioned/rebuilt Merc's (for a Bravo1) available locally, and new engine is likely to be about 18k-20k Aus Bills fitted.

Eventually found a local mechanic (Avante) who had just pulled and traded-in a 2010 5.0LMPI (for Bravo1) from a boat who's owner wanted to re-power with a bigger engine, they'd checked it and replaced manifolds/risers/pumps belts etc and said they'd do me a deal (about 6k bills + fitting) - but they would "of course" check my engine out first (I thought what's the chance they'll say my engine's OK when they have a engine they want to sell me...).

To their credit, they called me back in a couple of days and said my motor's repairable. Looks like what had happened was that one of the exhaust flappers was burnt out (obviously when the engine had been overheating 6 mths ago) and must have let water back up the exhaust (obviously when I went in reverse), which then filled the engine with a belly-full of water and eventually caused the hydrolock (fortunately not while underway but only on the starter). They checked compression and all OK. Valves & everything else seem OK. They were going to pressure test the manifolds/Risers - but I suggested they should be replaced anyway as I'd got 10yrs out of them. Replaced oil (3 times to get all the water out). Overall a MUCH cheaper outcome than I was first expecting.

Everything seems to be running fine again now. I guess time will tell if it's going to cause any other ongoing issues (any suggestions on what to look out for?)

Raft61 · **Posted:** Mon Jul 13, 2015 7:23 am

As a PS to above...

I was away on vacation when having the overheating problems back in January and had to use whatever mechanic I could get a hold of where we were (on the Gold Coast). Problem seemed to start after I got stuck on a Mud Bank.

He had two attempts at fixing my overheating problems (each time it overheated it was causing the alarm to sound, had to turn engine off and radio for a tow home).

After the third time I thought I'd wait until I got home to sort it out myself. Had he (or I) thought to check the flappers after the overheating, I might not have suffered the above...

Pic of the burnt flapper...

Raft61 · **Posted:** Mon Jul 13, 2015 7:55 am

PPS: The manifolds & elbows didn't look too bad. I probably could have got another couple of seasons out of them (which is why they wanted to pressure test them). Not bad for 10yrs in salt water.

But I thought better safe... Change em out.

LouC · **Posted:** Mon Jul 13, 2015 9:33 am

I had something similar with the Cobra 2 seasons ago. What happened was, I did such a good job cleaning out the obstructions in the lower gear housing that the extra water flow and pressure from the large Cobra impeller popped the hose off that goes from the transom mount to the P/S cooler!! Which promptly overheated the engine and filled the bilge with salt water. Well I thought the engine was trashed but I got lucky too. No water in the oil. While I was waiting for Sea Tow I checked the ex manifolds and they were 375*F. Yes that hot but not cracked (checked with acetone). Exhaust flappers were vaporized. Pulled the drive to get out the melted pieces.
I split the drive AGAIN to check the water tube grommets because they can get trashed from overheats.
Engine compression was fine, still running fine now 2 years later. Thank you General Motors. Long live cast iron.
Do you have the old style Merc manifolds, if so Id consider the Hy Tec one piece stainless units. They will last much longer and safeguard your engine no joint there to leak.

GottWhat · **Posted:** Mon Jul 13, 2015 9:54 am

Glad they were able to save your old engine, good luck!

Raft61 · **Posted:** Mon Jul 13, 2015 10:17 am

Yep, hopefully a good save. Fingers crossed nothing else comes up from it.

I've got the older style (but dry joint) Mercruiser Manifolds, not the catalytic ones. Had actually spoken to the guy from HyTec about two months ago and was thinking of replacing them with the SS one piece units at the next service (They're so much lighter and I believe they provide better airflow/tuning). But because all this happened so quickly, I asked the mechanic whether I should get the SS ones. He suggested that he's seen a few of them crack and wasn't a fan of them - should have gone with them (They're reasonably priced and they look great installed too).

LouC · **Posted:** Mon Jul 13, 2015 10:44 am

Interesting. Well if you have the dry joint system then you're in better shape regarding leaks for sure just plan on changing them out again in 6 years, maybe because you'll be ahead of the corrosion process. I have the one piece cast iron OMC manifold/riser units on mine and they are no longer available. So next time I will have to go with a standard system. Just as an FYI, here is what the outlets look like after 5.5 seasons in our salt water vs new:

https://www.dropbox.com/s/co8mqd4vi8qze ... w.jpg?dl=0

Notice how one outlet is totally clogged. Engine was starting to run a bit hot, but it wasn't the cause, it was the damn barnacles on the water screen!!
These were able to be cleaned and re-used but I had the new set all painted up so I installed them (2011) so in 2016 they will come off for an inspection.
I'd love to be able to use the Merc dry joint system on mine but its more complex because the exhaust hose diameter is different from OMC/Volvo (Merc is larger).

deafwish · **Posted:** Mon Jul 13, 2015 6:16 pm

I don't see how a burned flapper would allow for water to come back up the exhaust while the engine was running & allow you to get back to the boat ramp.
I'd almost bet a left nut that your exhaust manifold leaked water in to your cylinders between the ramp & home, which caused the hydro-lock.
I've been there & done that. With some prompt action, this can easily be fixed.
I now run the Hi-Tek Manifolds & would never go back to conventional cast manifolds...

viewtopic.php?f=11&t=13645&hilit=backfire&start=0

Raft61 · **Posted:** Mon Jul 13, 2015 8:43 pm

Yeah, actually you're probably right about the flappers. If it took water thru the exhaust like that it would have hydro locked straight away...

Also I still don't understand how that much water makes it from the cylinders into the sump (past the rings). Or how much water it takes to froth up the oil so that it looks so far overfilled. Oh well, I guess I'll find out soon enough if there's something else that caused it...

Now I'm really disappointed I didn't get the HyTek manifolds while I had the chance.

deafwish · **Posted:** Mon Jul 13, 2015 9:29 pm

Your starter will create a massive amount of rotating torque on your piston that is hydrolocked.
I'd assume you'd have a couple of hundred PSI of water pressure pushing past your piston rings!
My oil looked like a milkshake and was only approx. 300ml over full.
Buy an oil analysis kit and perform one 10 hours after the repairs.

Raft61 · **Posted:** Tue Jul 14, 2015 4:39 am

Thanks Deafwish,

Didn't know you could get an oil analysis kit... Will do!

Yeah, I get the pressure under hydro lock, but isn't there much more pressure under normal compression and actual combustion (as a gas) which doesn't get past the rings (or is that blow-by)? Although I guess under normal combustion the piston is free to move down, whereas under hydro lock the pressure stays and has to eventually go somewhere... (did I just answer my own question?)

LouC · **Posted:** Tue Jul 14, 2015 9:20 am

Fluid dynamics:
Air is compressible
Water is not
That's why under cranking hydrolock can actually bend connecting rods, break starters etc.

Since you have the dry joint manifolds, a leak around the joint between manifold and riser is very unlikely, that much water in the engine is more likely to have come from failed manifold or risers. The dry joint is a big improvement but cast iron still rusts in salt water. Its a good idea to take off cast manifolds every 5 years and check them, and also look in the exhaust ports and check the valves, you will see rust there even when a leak is just starting. Take a look at this pic of my engine, this was in 2011 the last time I changed the manifolds, even though its an old engine (original 1988 heads never off) you can see the exhaust valves are just normally colored, no rust at all. 100% salt water use the last 15 or so years.

https://www.dropbox.com/s/u3w9g3qvuxycb ... 1.jpg?dl=0

The rust on the cyl head between the exhaust ports is just from the gasket that holds moisture against the cast iron. There was no rust at all in the exhaust ports or on the exhaust valves. This is what you want to see.

Raft61 · **Posted:** Mon Jul 20, 2015 6:55 pm

Thanks for the pic LouC. Thanks all.
Yep... Will definitely make sure I pull manifolds off after 5yrs to check (not wait 10years ...for it to fail)

Raft61 · **Posted:** Mon Sep 14, 2015 1:16 pm

Well. Looks like the water's coming from somewhere else...

Was getting the boat ready for a day out and checked the oil... It's starting to milk up. I don't think it's just residual water in the oil lines etc, so will have to look further to see where it's coming from.

My guess is head gasket or head, as I had suffered from some overheating problems end of last season before I managed to sort out my cooling problem (blocked water flow). Might have warped or cracked a head (more pain coming...)

deafwish · **Posted:** Mon Sep 14, 2015 4:00 pm

I'd perform a leakdown and/ or compression test.
Change your oil ASAP!

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Hydro Locked Mercruiser 5.0MPI Engine

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