Over heat and then later hydro locked?

[jtkr996]

Hello,
I have a 1995 Regal with a 5.8Fsi.

I have a (now) recurring issue where after a mild overheat the motor hydro locks after being shut down on the trailer. Water enters the cylinders via the exhaust ports.

2 years ago I launched in some dirty water (driftwood/debris from a big storm) and before I could get out of the no wake zone she overheated. (gauge never went over 190-200 but it usually runs 150ish) After cooling it off I checked the raw water pump and it was clear so I decided to put it back on the trailer.

It ran fine and powered onto the trailer. When I made it back to the top of the ramp I attempted to start the motor and it was hydro locked. Back 3 cylinders on both sides had water in them.

I Pulled the plugs, got the water out and it spun fine. I decided to change the manifolds as they were the originals.Also changed the t-stat (my presumed cause of the overheat) put it together and all was well. Ran great all of the 2016 season and had it out the last couple weekends with no issues.


... until now. Launched this Sunday (after running great all day Saturday) Exact same scenario just happened again. There was lots of Debris at the ramp. Got out of the no wake zone and noticed it was overheating. Let it cool, pulled a hose from the Raw water pump and it was not blocked. Decided to put it back on the trailer,

I shut it down and even restarted it once before pulling out of the water no problem. A half hour later on dry land I tried to turn it over and it was hydro locked.
Pulled plugs, same issue. Water in the exhaust manifolds and cylinders.

I assuming the debris had something to do with the overheating, otherwise it's a huge coincidence. I'll plan to replace the T-stat again and make sure they system if flowing.


My real question is, is there any likely scenario where I didn't hurt my manifolds / risers?

Is there some other possible explanation where this water could have seeped in?

The only options I can think of would be the joint between the manifolds and risers, but I'd expect to see some kind of visual sign but the gaskets looked like new (because they almost are)

Or if somehow there was lingering water in the system that the exhaust pressure was keeping out until I shut it down.


I really hate to spend the $$ to replace the manifolds to later find out I didn't need them. I've overheated the boat twice before due to a bad raw water pump and never had any hydro locking issues. They just don't seem like they would be that fragile?

Anybody have a similar experience or ideas on what could cause this besides cracked manifolds or risers? Somebody please validate my wishful thinking...

Thanks in advance,

 

[jtkr996]

Follow up:
I found a old bulletin from Volvo saying that a overheat may cause the gaskets at the riser/manifold to leak. They changed the gasket material as a result.

I spoke to one person that says if I have water in the cylinder it's got to be a cracked manifold.

Another I spoke to says that gasket area is a very common spot to leak. The same person also said if I didn't get the manifolds hot enough to discolor or burn up my exhaust bellows then no way I got it hot enough to crack them.


Obviously I want to believe my manifolds are fine and that water just got by the gaskets, but why would that happen after shutting the engine down? Wouldn't the water stop flowing up thru the riser as soon as the circulating pump stopped?

 

[bruceb58]

You need to do a pressure test on your water passages of your block. It's possible you have a cracked head or head gasket.

You replaced both your risers and manifolds right? Did you use OEM manifolds? Did you use the Volvo gasket between the manifold and the risers?

 

[Lou C]

An easy thing to do is test the manifolds first. Take them off and prop them up so they are level on the ground. Then carefully fill them with acetone and watch the ex ports that match up with the cyl head ports. Look for wetness that would show a leak. The acetone will find a smaller leak than water because it has less surface tension..
You also might want to do a comp test and leak down test to see if you have a blown head gasket. On the Ford V8s I'm not sure but I wonder if overheating can cause the intake hadket to fail letting water in an intake port. It does not sound like it got hot enough though.

 

[Lou C]

If they do not leak you might want to take them and the risers to an auto machine shop to get the mating surfaces milled perfectly flat.

 

[Lou C]

There are a number of sources of water in a marine engine; I had water in 2 cyls that I traced to blown head gaskets. The cyl heads also had cracks in the center cyls (V6) but I did not have water in those cyls. This engine had normal comp test results because of the way the head gasket blew. The exhaust msnifolds did not leak.

 

[Scott Danforth]

pull the manifolds and do an acetone test for cracks. you will know immediately