OverHeating Temp 43 mercruiser

"Well i have a 99 searay with

"Well i have a 99 searay with as 4.3 merc with a alpha one outdrive. It also has a closed cooling system in it. But not entirely closed. Seawater only goes into my manifolds. i got this boat used. The temp was normal at 170F degrees. But the very last time i took it out for fishing the temp started going up. slowing moving pass 180F
then the temp alarm went off, so i shut it down.
Then i grab my emergency tools out and remove the termostat. That stopped the needle from going pass 180F. So i kept on doing what was planned for the day. the next week i bought new manifolds a 2 piece one (i have a 1 piece) thinking it might be the reason for the increase of temp. I also saw my water shutter were not there. what happen to them? Is there a aftermarket one the is metal rather that plastic. Do you think my engine is ok. What else could be the reason for overheating?"

"You bought it used. Did the

"You bought it used. Did the previous owner have the O/D sea water impeller changed at some time? The heat exchanger could need to be cleaned--cooling tubes are narrowed due to corrosion build up. Is the belt tight on the circulation pump? Maybe you just sucked in some debris in the lower O/D water inlet. Two screws hold it in place. Check the bellows for cracks--it is about time to replace them if not already done.

If you run it out of the water with a garden hose and it does not overheat, but it does overheat in the lake, then that is a good sign the lower unit water pump needs replaced. The garden hose is providing the water pressure to keep the water moving. A failed impeller can not push enough seawater thru the heat exchanger to remove the heat from the engine coolant.

The inlet hose from the engine to the exchanger will be hot and the outlet should be warm. If the outlet from the exchanger to the engine is almost as hot as the inlet, then the exchanger needs to be checked.

Is the coolant in the exchanger fresh and a green color or a dark rusty color? The dark color means it has been neglected by the first owner.

Since the thermostat is out, you can change the antifreeze by draining the block; capture the fluid and dispose of it at a recycler. Then backflush the engine and the exchanger with a hose until it runs clear. Drain the water out of the block and exchanger and put in a 50/50 mixture of distilled water and antifreeze and a new thermostat and pressure cap for the heat exchanger. Don't know about the flappers. Good luck."

"No the previous owner didnt d

"No the previous owner didnt do anything to it. He justed used it the parked it under a tree, the boat wasnt cover and the drain plug still on. For four years. I got a good deal on it. All I had to do was have the alternator and starter rebuilt. I also did a complete fluid change. and plugs rotor cap. About the flapper or water shutters Could that have been the reason why i see alittle rust on the exhaust valve? I also think the impellor is original. Is it easy to replace? How?"

"Minh, The exhaust flappers ar

"Minh, The exhaust flappers are not your problem. They simply keep water from backing up into the exhaust manifold, from the ocean or lake, if you suddenly come to a stop. Rust on the exhaust valves is a sign that the manifold may be leaking. You have replaced that, so that issue should be resolved. The impeller in the outdrive should be replaced, since it has been 7 years or so. Purchase a manual and read the procedure. It is not too hard to do"

"Mihn: Since the boat sat for

"Mihn: Since the boat sat for a long time it needs a good out drive inspection. There are shift linkages and drive shafts with grease fittings on the U-joints of the Out/Drive inside the bellows that require lubrication. The O/D must be removed to do this work.

The bellows and sea water hose are nearing their useful life and you should consider replacing them when the O/D is removed especially if the other owner left the O/D in the up position which causes the rubber in the bellows to become set (used to being in that position)in the up position. It happened to me.

Now that you are moving the O/D up and down it will develop a crack in it and seawater gets in and ruins the shafts, bearings, coupling etc. Very expensive repairs. The coupling cost me $800 to replace.

The gimbal bearing can be inspected at this time and lubed or replaced if needed along with a cleaning, inspection and lubrication of the engine coupling. VERY IMPORTANT.

These procedures can be done by you if you follow the instructions in the servcie manual and use an alignment tool to reinstall the O/D. Consider having a professional do this work and watch them do it to learn.

The parts are not expensive except the coupling. Engine must be pulled to replace it. Remember, you pay for what you get either now when it is less money or later when the O/D is ruined and it's $1,000 to $2,000 for a replacement O/D.

My bill for a new engine coupling, water pump kit, bellows kit, new gimbal bearing (rusted) and labor was $1,450 by an independent marine mechanic. The dealer wanted $3,500."

Thanks for the tip guys. I jus

Thanks for the tip guys. I just bought a new set of manifold. Is the metal flappers better than the plastic one from Mercruiser?