1983 350 mercruiser 260 I/O overheating

Ok this seems like a diferent peoblem than what other people have had. I got this Baja 20ss with a Chevy 350 mercruiser 260 I/O in it from a relative that let it sit for 3 years. I replaced the whole impeller assembly and the therostat on top of the motor. It pumps water well thru the thru hull exhaust system. I have noticed that the starboard side seems to put out more water and stays way cooler, you can leave your hand on the manifold and riser all day long. The port side runs way way hotter, you can only leave your hand on on the riser for 3 seconds then OUCH! Port manifold is hot too and there is less water going out thru the exhaust on that side and way more exhaust smoke than the other side. It quited out on the lake the other day and we were ripping up the lake for 5 minutes then it smoked a bit and wanted to stop and didn't want to start up then. I had to be towed in, how embarrasing. It cooled down and I coulden't believe that it started up again. It starts right up and runs great but the port side heats up badly. Any advise seeing that it's only the port side that has a issue would be appreciated. It will heat up on the trailer in neutral you don't need to have a big load on the system. Could it be the circulating water pump on the front of the engine or a head gasket?? Please help, I want to go fast again. "Ricky Bobby"

 

There are drain plugs on the manifolds and on the block.
Turn them loose and you'll find that on the port side no water comes out.
The water passages in Mercruiser exhaust manifolds corrode badly and flakes of rust can clog them completely, especially after prolonged storage.
So you have to remove the hoses and the port riser to remove the debris.

 

Thanks it's dark out now but I will try removing the plugs tomorrow to see what comes out and I will also remove the port riser and manifold to see if there is any build up blocking the passages. Thank you for your help, I will write back to say what happened. As a side note, today I checked the plugs and they all looked good and there gapped correctly. I checked the fuel/water separator and there was only good gas in it, no water that I could see when I put the gas in a clear glass bowl. I told my neighbor about the problem and he knows a bit about boats. He told me now that I have done all this stuff to try to fix it. Put it in the lake again and not just with the on the ear muffs on because the water pressure may change the results. I told him with it warmed up and running I checked the outside temp of the risers with the temp sensor on my fluke meter and the port side is running around 140 degrees and the starbord side is about 105 degrees with the earmuffs on running off cold hose water. He said about 140 degrees is normal for my motor and it's strange that the starbord side is running cool but mabye the lake will change it. Who knows but I will post when I find out. Thanks...

 

OK I had a few minutes after work and I put the boat in the lake and tried it. I just let it idle for about a half hour and kinda did some circles not real fast. After it was way warmed up some water kinda like condensation was comming out of the black hose that goes from the port side valve cover to the side of the carbutator, I think they call it a flame arrester or something. Anyway a small amount of water was comming out of the hose right there at the carburator and making a mist was it hit the motor. Kinda like steam and the faster the engine revs the more steam you get. so the starbord side stayed cool and the port side got really hot again. The temp on the port riser and manifold got to about 160 degrees. the other side you could leave your hand on all day long. Oh and the 2 hoses that go to the front of the risers from the place the thermostat is mounted in stayed really cool not even warm when all the other hoses were hot!!!

 

The hose from the valve cover to the flame arrester is supposed to feed crankcase fumes back to the intake. If you see water there, you probably have a cracked cylinder head or a blown gasket. That is not unusual in an engine with a cooling problem.

You cannot diagnose properly by just putting your hand on hoses. A cold hose can be filled with cold water but it may also be empty because there is a blocked passage. So get your tools and dismantle the cooling system.
And while you're at it, check the condition of the circulation pump, the impeller may have lost its wings.

 

Ok I took pretty much the whole motor appart yesterday and found what I think the problem was. On the starbord side, under the manifold there is a crack or opening in the block that goes from one of the water passages under the cylinder head to under the manifold which is where the water was going to, under the manifold. The manifolds are in great condition but the water passages on the cylinder heads were pretty blocked up right where the gaskets go. My friend says the block can not be fixed. I may be ignorant but I have to ask, can ya fix a small crack like this with JB Weld or anything? or No? I know it's a long shot but is it worth trying it or do I need to go spend $1200 on a short block?

 

Take it down to your local welding shop. They'll have welded up enough blocks to tell you if it's possible. No goo in a tube is going to cure your engine's illness. It really depends on where the crack is.