1999 Mercruiser 4.3L V6 Alpha One

My dad gave me a boat..as a gift! Ha!
My question is I can start the boat in the driveway using muffs and it runs fine. I then put the lower unit in a large bucket of water covering the water intakes and it won't suck in any water. Bad impeller? Bad water pump?
Any suggestions as to my next "fun" step?

Yes. You need to check your impeller.
When you ran it on muffs did you notice water shooting from the exhaust ports?
Removing the lower unit is simple. There are plenty of YouTube videos if you get stuck.
I would be tempted to replace the impeller anyway while you have the leg off.
Try this and come back if it hasn't made a difference.

Of course do not run the engine for ages if you're sure there is no water being sucked through it as you may cause engine damage

Unless you can get a big enough bucket to go 3 or 4 inches above the trim cylinder you wont see water and will most likely damage the impeller. If it runs normally on the muffs, thats all you need to know until you get it in the water at cruise rpm

When running on muffs, yes water was coming out. BT Doc- not sure where the trim cylinders are located. Sorry for my ignorance. I'm learning as I go. The container I'm using covers the vents on both sides of the unit. The same place where I attach the muffs.
The next question will be "Why are you doing that? Just use the muffs!" Or put it in the water!
Truth be told my father gave me this boat after not winterizing properly. I suspect a valve cover issue. Also the boat was left exposed to rain with oil dipstick out and had water in the oil. I have since pumped everything out, changed the spark plugs, distributer cap, ignition coil, rebuilt the carb. I'm using the bucket method to recirc the water and adding Blue Devil. Probably not the best fix..but I'm willing to give a try.

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I’d it wasn’t winterized properly and you have water in the oil you will have more than a valve cover problem. I’d suggest pressure testing the cooling system so you know what you’re getting into $$$ before you put a lot of money into it.

A boat that's free (or cheap) is neither. You're looking at a possible engine replacement due to a cracked engine block. However before all the doom and gloom, do your testing IN THE WATER, tied up at the dock. Get the engine warmed up and check the temp gauge and by touching the exhaust elbow. If you can't touch it cz it's too hot then shut the engine off immediately as it's probably not pushing water thru. Running on "muffs" in the driveway doesn't tell you if you have a bad water pump impeller cz the water is forced thru the engine under pressure.

Thank you for all the input. I've replaced the impeller ( there were a lot of gaskets missing, boat is clean as a whistle..looks like someone was just in a hurry)and started the boat back up using a large bin. Ran for about 30 mins..it was pulling the water fine, temp running 175-180. Then noticed the water output slowed to a trickle. I'm not sure what caused it to slow down. Temp remained good. I'm taking the lower unit back off now and retracing my steps. Yay! Good times.

The exhaust going into the water tends to make a froth of the water, which doesn't pump so well. Seen that happen before where a perfectly good set up doesn't pump.

Jeff

Reelchicsfish said:

Thank you for all the input. I've replaced the impeller ( there were a lot of gaskets missing, boat is clean as a whistle..looks like someone was just in a hurry)and started the boat back up using a large bin. Ran for about 30 mins..it was pulling the water fine, temp running 175-180. Then noticed the water output slowed to a trickle. I'm not sure what caused it to slow down. Temp remained good. I'm taking the lower unit back off now and retracing my steps. Yay! Good times.

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Take pictures of the lower unit where the pump mounts up. Especially where the black rubber filler block is, paying attention to the aluminum water dam. We are looking for rot on the water dam.
Did you replace the whole pump or just the impeller? On a gen2 Alpha if you use an after market pump and housing, the liner in the pump will rotate and close down water flow.

While you have it apart this time, if you bought an aftermarket pump or just changed the impeller, go to your local Merc dealer and pick up a complete OEM pump kit with the lower seal carrier, a new water dam and filler block. Do it right.

o2batsea said:

A boat that's free (or cheap) is neither. You're looking at a possible engine replacement due to a cracked engine block. However before all the doom and gloom, do your testing IN THE WATER, tied up at the dock. Get the engine warmed up and check the temp gauge and by touching the exhaust elbow. If you can't touch it cz it's too hot then shut the engine off immediately as it's probably not pushing water thru. Running on "muffs" in the driveway doesn't tell you if you have a bad water pump impeller cz the water is forced thru the engine under pressure.

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Yup. I think that's where I'm at. I finally took the heads off and took them to a machine shop. Sadly, the guy said they look great. I'm pretty sure that's one of the only times I was disappointed to hear something looked good. I did take some pictures of the block. I'll try to post them here. Looking at them top left I'm guessing 5 and 3 it looks like a crack. Then again at 7 lower left. I'm gonna clean up a little better and inspect them more. Now the question is do I buy short block and replace everything, or pull the trigger and buy a long.


P.S. Until today, I thought the difference between a short and long block was length.

Reelchicsfish said:

Yup. I think that's where I'm at. I finally took the heads off and took them to a machine shop. Sadly, the guy said they look great. I'm pretty sure that's one of the only times I was disappointed to hear something looked good. I did take some pictures of the block. I'll try to post them here. Looking at them top left I'm guessing 5 and 3 it looks like a crack. Then again at 7 lower left. I'm gonna clean up a little better and inspect them more. Now the question is do I buy short block and replace everything, or pull the trigger and buy a long.


P.S. Until today, I thought the difference between a short and long block was length.

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no this is one case where length doesn't matter, my thinking your options are (low road) 4.3 out of a junk yard, new head gaskets and brass freeze plugs. High road new or rebuilt long block. Need to check you exhaust manifolds and intake water cross over for cracks as well.

Reelchicsfish said:

.............. Now the question is do I buy short block and replace everything, or pull the trigger and buy a long.

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What is your skill level regarding SBC engine work?

Choices:

....... Buy a short block and have your cylinder heads gone through.
Install them with the correct head gaskets.
Adjust your cam followers using the 6 stop static procedure.

....... Buy a long block.
Have the shop adjust the cam followers using the 6 stop static procedure.



By the way, the brass plugs are "casting core plugs", aka "welch" plugs.


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