water in cylinder(s)

Big Block 454 MPI Magnum. Cruising along, temperature spiked. checked drive pickup, no restrictions. Ran compression test, two cylinders low. Pulled thermostat and ran for another few days and water intruded # 5 cylinder, and bent a pushrod. Disassembled engine, assumed head gasket(s) blown. Could not find anything wrong with head gaskets, no visible cracks in head nor block. Also water in # 4. No water in oil pan, but top end milky. What else could it be? Risers and manflds are only a few years old.

Re: water in cylinder(s)

Woohoo, pretty sure I know this one -and you've caught it before it totaled a head. The Merc I/Os have a built-in obsolescense. That's the only way I know how to describe it. The fault is the gaskets on the exhaust manifold elbow risers, they're the upside down Us at the rear of of each head. The exhaust manifold has a cooling jacket which recirculates water to cool the exhaust. This is what is dumping water in your back cylinders. What happens is that the riser has thicker wall to the outside then to the inside. So when the gasket goes it leaks to the inside first. The water jacket water will drain into the back cylinders once the engine is turned off. On cranking to start next time there will be a knock from the water in the cylinder(s). This typically blows the head, piston or engine block so your leak is still small.

I recommend:
1) Machine home the head(s) before re-installing them with new head gaskets. Use non-retorquing head gaskets.
2) Remove the elbow risers -you may have to cut a small area of fiberglass engine housing out to get to the rear bolts. Clean the riser surface and matching manifold surface of the old gasket material. It will be a mess since they're paper gaskets and water has intruded. Make sure both matching surfaces of the engine-side are smooth. I've sanded mine before. The side towards the engine (or to front of boat) is the problem seal. The back seal is irrelevant as it will drain out the exhaust if it ever leaks.
2) Fix the elbow riser gaskets!
-Purchase new gaskets and Permatex RTV Blue silicone sealant. Work the silicone into both sides of the (paper) gasket until saturated. Allow 24 hr.s to dry. The critical seal is the joint towards the engine. Put the silconed gaskets there and torque to spec.

I hope you save your engine. I bought a nice 165 for $300 which blew up from this fault. The block was blown so I had to put in a rebuild. That was 15 years ago. Never changed the elbow riser gaskets again and no problems since.

Re: water in cylinder(s)

I forgot to mention that the silicone should be worked into the edges of the gaskets too, particularly the smaller holes which are used for the cooling water. The cooling water must not be able to come in contact with paper gasket material, just silicone and steel.

Re: water in cylinder(s)

The temperature may have spiked due to a plastic bag over the water pickup. When you stopped and shut the engine off, the bag fell off.
This has caused more than one overheat trust me. If it overheated and warped an exhaust valve it will suck water back into the cylinders at idle, plus the riser/manifolds gaskets could start leaking due to the overheat.
Have the valves checked, and install the head back on per the OEM service manual. Install new OEM riser gaskets and DO NOT use the method above. With OEM gaskets, they are graphite coated and go on dry.
Here is the service bulletin on the gaskets. http://www.boatfix.com/merc/Bullet/99/99_10.pdf

I could give you a link to the OEM service manual, but for some reason, new people to the forum never give year or serial numbers for their engines.

Re: water in cylinder(s)

Don what's your beef with RTV silicone? I looked at the new gaskets and they do not appear to be impervious to water. They appear to be a combination of paper, metal and graphite, i.e. high-temp exhaust gaskets rather than water gaskets -which is their most important role with the elbow risers.

A simple test would be dumping one of the new gaskets in a bucket of water and coming back in a few weeks to check for discoloration and swelling.

In 30 years of boating and several Merc I/Os the elbow riser gaskets are the #1 cause of catastrophic Merc I/O failure. As a mechanic and board moderator you are free to disagree and with far more authority but I will stand by my assessment.

Re: water in cylinder(s)

Did you read the bulletin?

Re: water in cylinder(s)

Yes I did read the bulletin. I question the quality and suitability of the recommended gasket. I believe the reference part is unsuitable for sustained contact with water. As you know this gasket remains immersed in raw water from the moment the engine is started until the exhaust manifold is winterized or manually drained via the petcock.

Re: water in cylinder(s)

They aren't paper any more !!!!!!

I believe the reference part is unsuitable for sustained contact with water.

Click to expand...

I guess it's possible you know more about these new gaskets than the engineers, but I doubt it.

Re: water in cylinder(s)

Considering the innumerable engine failures attributable to the elbow riser gaskets I highly doubt the engineers remain ignorant of its shortcomings. But the purpose of Mercruiser engineers, iboats.com and mechanics is to generate revenue so I'll just stop here. You have my regards. Good day.