Merc 470 Rebuild, issue with cooling system

[alexr254]

We were running the newly rebuilt engine today for a few minutes, out of the boat with a running water hose connected to the inlet, for the raw water cooling.

The raw hose water kept on running for a few minutes when engine was shut down.

We later found water on all 4 plugs and in all cylinders... OUCH!!
We quickly removed all water and dried it out..

Now were trying to figure out what caused this.... Could it have been the raw water hose running even while engine was off? The water was coming out of the exhaust tube so we figured it would not fill up into the open cylinder from the exhaust manifold.

Somehow water got in there, and we have no visable leaks...

please help this is our first ever rebuild, and were running into newbie issues i guess.

 

[Don S]

Re: Merc 470 Rebuild, issue with cooling system

Was it straight water or antifreeze in the cylinders? You do have AF in the engine don't you?

If water from the raw water side, the only place it could be is the elbow leaking into the exhaust manifold.

 

[alexr254]

Re: Merc 470 Rebuild, issue with cooling system

It was straight water, no antifreeze. We do have a 50/50 antifreeze in the cloosed cooling part of the engine.
We just replaced the exhaust riser gasket..

Can it be because we have straight water running while the engine is off?

 

[Don S]

Re: Merc 470 Rebuild, issue with cooling system

Can it be because we have straight water running while the engine is off?

No, it shouldn't be a problem at all.
You changed the riser gasket, but what shape was the gasket surface of the riser in. It must be flat, and clean, and the passages through the riser must be clear, and no holes in the wall of the riser between the water and exhaust passages.

 

[natemoore]

Re: Merc 470 Rebuild, issue with cooling system

Here's a TSB of that subject:

View attachment MSB 88_02 leaking exhaust elbow.pdf

 

[alexr254]

Re: Merc 470 Rebuild, issue with cooling system

Thanks

I am using 27-18272

We ended up getting all water out, and trying it again without running water while off.. Whatta you know.. It didnt happen again...

I am guessing its due to high water pressure coming from my hose, it was filling up too fast and the water was getting through the exhaust manifold into the cylinder holes while the engine was shut off.
There definately was no leaks, surfaces on the elbow and manifold are flush, and were done by a machinist.

 

[natemoore]

Re: Merc 470 Rebuild, issue with cooling system

Could an exhaust shutter back up the water enough to allow it to fill up the exhaust riser and spill down into the exhaust manifold and then into the cylinders?