Hi. Smoke or possibly steam from the starboard exhaust pipe. nothing from the port pipe. After a high speed run it smokes/steams to the extent that fellow boaters stop and offer me assistance. When the engine cools down after some minutes of idling, it still smokes but maybe one tenth of what it does right after the run. Sparkplugs look fairly normal, temp is OK, oil is OK. Exhaust manifolds are cool enough for one to be able to lay a hand on them without problem. It is fairly cool outside here ,maybe in the low 50s. Engine is a 1998/99 502 MPI with Gil exhaust and silent choice. Any ideas what it could be?

I think you get more steam when the water starts to cool down. I would check the gaskets between manifold and risers. My old motor had a lot of steam right before it puked from an exhaust failure.

I would worry about it. The steam may be due to a bad riser gasket, as Dave M suggested, or a bad manifold or riser. The steam is not going to do any damage, but standing water in the manifold after shutdown will rust the exhaust valve seats and stems.

I would pull the riser and check for water in the manifold. I would also check compression on that side.

Dave

It is Gil manifolds with a jumper hose between the manifold and the riser. So there is no water passage through the gasket that can leak. If water enters the exhaust before it is supposed to it must be a hole in the manifold or riser somewhere. There is however no sign of water on the plugs. I will do a compression check and see if it is OK. Any other ideas?

Do the manifolds and risers have water passages that are just blocked by a solid gaske ? Some are built this way and are not true dry joint, if this is the case you may have a gasket failure. One way or another if it steeming so much that other boaters offer assistance something is defenitly wrong If there are no gaskets or water ports I would suggest pulling them both and having them checked. Could also be the sea water pump, if the housing is worn and it is not flowing enough water you can see steam but dtll not overheat. When was the last time you serviced it ?

It is a true dry joint, no water reaches the gasket between manifold and riser. The waterpump and impeller has just been changed. I also picked out ALL the pieces from the old impeller. So, what is left.... a hole in the manifold or riser?

I have now done some further troubleshooting. During engine warm up there is no smoke or steam at all from either pipe. That indicates that there is nothing wrong with the engine itself ie no burning of oil. There is probably no water entering the exhaust in the wrong place either, since then it should steam all the time. However, there is less coolingwater coming out of the starboard pipe and the water from the starboard pipe is consequently some 40 degrees F warmer. For some reason the water is unevenly distributed between the manifolds. Is it as obrien99 says that this is normal on a BB Chevy?

He also said that the starboard side is the cooler side.

Is this a problem that started recently or has it always done this? You either have a flow resitriction somewhere on the starboard manifold cooling, or there is higher exhaust back pressure (stuck or partially stuck silent choice) on that side.

I guess you did not do a compression test? I still think it's a good idea.

Dave

Dave, I will do a compression check. What shall I look for,ie what is the connection between the compression and the steam? A blown head gasket?

Yes, they rarely are equal at idle. You might check your water pump impeller next chance you get. When you have a water leak in the head or manifold, it will steam all the time.