Overheating and hydro locked

[Mike Harding]

Hello everyone , my motor overheated from a bad thermostat and hydro locked , I replaced the thermostat and it ran normal with muffs on but when I put it in the lake , it hydro locked again, I pulled the plugs while on the lake and cranked it over and water was pumping out of the cylinders like a pump. Question is what can cause this much water into cylinders? Would a bad gasket do this? It’s a lot of water, no water in lower end of motor and again it didn’t do this with muffs on it , ran normally for 45 mins onshore and kept temp . Motor is 2005 Volvo Penta 5.7 Gxi-F

 

[Scott Danforth]

first, welcome aboard

doubt it was a bad thermostat, normally its from lack of water flow from a failed raw water pump.

if you did a serious overheat, you could have lost either head gaskets or the intake gasket. if any amount of water hit the exhaust castings, when hot, they can literally explode or crack.

 

[Mike Harding]

Thank you, my thermostat wasn’t allowing the raw water to circulate , thus the overheating . But if that wasn’t the likely cause I’m all ears. As for the water into the cylinders only when in the lake not when on muffs , you think intake or head gasket? Literally like a pump with the amount of water entering and exiting the cylinders with every motor rotation. Would a gasket allow that much water in? And I believe I suffered from what’s called passive hydro lock , motor heats up and is quickly turned off causing the heat of the manifolds to draw water up and in, it’s a known phenomenon but again if that’s not the likely situation then I’m listening. Just not sure what to take apart next it’s only on one side of motor and it’s a lot of water

 

[kenny nunez]

You can start by removing the spark plugs on the side that is getting water, connect a garden hose to the front of the manifold water inlet and just let the water run and see if water starts flowing out the cylinders.

 

[Scott Danforth]

I would pull the manifolds and acetone test them

is this the first time you are using the boat this year?

 

[Mike Harding]

I’ve been using it all year , I think my thermostat packed it in, and overheated the boat , that’s where this all started , overheated and I turned it off then tried to start again and it was hydro locked . Changed thermostat and ran it for 45 mins in the driveway And thought alll was well in the world so took the boat out and once on the lake it immediately overheated and hydro locked again

 

[Lou C]

Well if it blew head gaskets that can let water in but not as much as bad exhaust. Both are likely to let water in after the engine is shut off and cooling down. Not much if at all when the engine is running. I had some water in a cyl after blowing HGs but not enough to hydro lock.
You can drain the block & exhaust of water and then remove the plugs spin it over and blow the water out of the cyls. Spray fogging oil in the cyls to lube them. You can do an air pressure test of the cooling system to see if the HGs are leaking. And acetone test the exhaust manifolds

 

[Mike Harding]

Ok so my next question is what would allow the motor to pump water into cylinders when turning it over , almost like the pistons are acting like pumps and causing vacuum and bringing water in , is that possible ? Exhaust fills with water due to suction from pistons?

 

[Lou C]

It can run in from leaky exhaust after engine is shut off or from a bad head gasket same thing

 

[Lou C]

I’d do a comp test and check your exhaust

 

[Mike Harding]

Just did a compression test basically even across all cylinders at around 150psi , not sure if that rules out head gasket or head issues but I’m optimistic. Next step is acetone testing my exhaust manifold , is there a way to test riser?

 

[Lou C]

Post up pics after you clean up the sealing surfaces . Not really a way to test the elbows but the acetone test (be careful highly flammable) is good for manifolds. You go by the sealing surfaces and how much flaking rust you see in the cooling passages. Sealing surfaces when cleaned up should not be pitted or uneven. They have to be really flat to seal.
Comp test results look good; to be on the safe side I’d do the air pressure test on the cooling passages to make sure there is no leakage. This would show a blown HG or cracked head. Yes you can have close to normal comp test results and have a blown HG that leaks water into cyl as the engine cools off. Happened to me 3 seasons after a bad overheat.

 

[Lou C]

My symptoms were rough running that cleared up as it warmed up from slightly sticking valves, water in a cyl and water in the oil. Combustion gas was getting into the cooling water esp as the engine is shut off. Then as it cools water would leak back into one cyl. But my comp test results were normal, none were low. So do the air pressure test and see if the cooling passages hold pressure. If so then good, the only other issue is a bad overheat can definitely crack cyl heads, mine were cracked in the center cyl of the V6 heads right at the valve seat, but this did not cause a water leak that was all from the blown HGs. My overheat was in 7/2013 and the HGs did not blow till 8/2016. So even if it seems fine, just keep that in the back of your mind, after its up and running check for water in the oil. Wound up installing these with Fel/Pro marine head gaskets and also upgraded my exhaust to the two piece system at the same time.

 

[Mike Harding]

Thank you for all the replies, so I did my leak down test and Center cylinders on port side leak down about 10psi at 50 . Can’t hear or identify where the air is going other than back out the spark plug hole as the insert is only hand tight. You mentioned a leak down test on cooling channels is this different than through your spark plug holes? Not sure if I should pull my head to have peace of mind or trust the gauges and say my problem is elsewhere. In my mind the problem is catastrophic as the amount of water entering the cylinders seems more than a bad gasket could supply. Hopefully all this discussion will help someone down the road

 

[Mike Harding]

Acetone test on manifold showed no leaks as well

 

[Lou C]

If you do a search on these forums you will find it. You have to make up a fitting to apply compressed air to the thermostat housing raw water hose opening and connect both feeds for the manifolds with one hose. See if it holds 15 psi

 

[Mike Harding]

Alright I’m guilty of going down the rabbit hole and getting lost in the what if’s and what could be. But my problem seems a lot like water reversion , whereby the valve lap is pulling water like a vacuum back into the motor. It’s typically on big blocks and at times on sbc but most often seems to be exhaust component failure on my setup . So my question is this, aside from manifold and riser gaskets which I’m replacing and knowing that my compression is good as well as leak down tests being all good, is there something in my exhaust system which might be causing or allowing water back up and in . Just spitballing at this moment as I’m waiting on parts and want to make sure I’ve thought of everything

 

[Lou C]

Well to start with you should measure the static water line of your boat in the water. If it’s lower than 14” you might need taller elbows

 

[Mike Harding]

Alright I did the coolant system pressure test and it holds at 20psi no problem, at this point I’m thinking install the new riser gaskets and see if it’s solved , probably all that was ever wrong but just seemed like too much water for a failed gasket, hopefully this is the fix . I appreciate all the help Lou thank you very much

 

[Lou C]

Glad to hear that. I would measure the static waterline when you put the boat in the water just to be on the safe side