sea water pump troubleshooting 7.4L

[1998233]

I tried to make two preventive maintenance steps before launching this year. (1997 233 Boat sits all winter in NY.)
1) SEA WATER (RAW WATER) IMPELLER
2) THERMOSTAT

I have done the impeller twice before so this was my third time. I do it every two years although impeller looks like new after two years. It is always a difficult job to do.

I had not done the thermostat before. Afterwards it seemed easy to complete.

Again did both of these as preventative; had no previous overheating issues.

Launched boat, drove slowly out of marina and after maybe 1/8th of mile noted temp was at 175 (not 160 as rated) and smelled warm. Turned it off. Let it set 5 minutes. Didnt really seem to cool off but wind was blowing me past marina at this point so started up drove 1/8 mile back to marina, got to almost 200 degrees and turned it off again. What is setpoint for overtemp alarm? Mine never went off.

Afterwards, noted the rubber exhaust bellows were brownish. Poured a little water on them and they were boiling hot as was the risers and manifolds.

Now I need to go back to marina and troubleshoot the problem. I think its the sea water pump.

How do I confirm the sea water pump is not working properly?

Should I pull the bottom outlet hose off and see if any water is coming out? Or will that shoot water somewhere electrical or otherwise undesired?

I do I confirm the thermostat is or is not working right?

[rabiddawg]

To confirm the thermostat is working you are going to have to heat some water with it submerged in it.

Are you sure you installed the thermostat correctly?

[1998233]

Not sure yet. Of course it is possible. I infer from your question you think it sounds more like the thermostat?

Other than upside down, (which I am not sure is even possible) how would one do this replacement incorrectly.

I bought the Mercruiser OEM kit at the marina. Used the new cork ring gasket and the gray gasket with the two tiny brass ringed thru holes on each end. I had 3 extra gaskets in the kit plus a black O ring I didnt use.

[Holy Smokes]

Make certain the correct gasket was used. I once had a stat housing on a 454 requiring a bypass notch.

[rabiddawg]

It may be possible to install the stat upside down. I don’t know. I’m just throwing it out there.

If the stat is in correctly but isn’t opening its going to run hot. Pull it out and drop it in a pot of hot water to see if it opens.

Look for restrictions and blockages in the water lines and coolers.

Good luck

[xlint89]

Make sure your sea water pump hoses are correctly installed.

If mounted in reverse, the engine and exhaust will get real hot, real fast.

Temp alarm should sound around 180* I believe

[1998233]

Water was not even reaching the thermostat. Havent checked it but highly doubt I messed thermostat up. I am now pursuing hypothesis that there was an air leak in the sea pump assembly. Took sea water pump all apart. Impeller blades were seemingly half one way and half the other. Was not impressed with O ring. Seems impeller did not reach the bottom and was therefore sticking out as high as the o ring AND there was a polished wear pattern on the metal plate.

[1998233]

Replaced entire sea water pump. Did not help. Seems intake hose/system is failed. Dont know in what manner yet.

[Big Block Power]

Hose could be kinked or pinched off at the transom mount area.

[xlint89]

Don't they call it Bravoitis when the intake opening has corrosion and closes up?

[Big Block Power]

Don't they call it Bravoitis when the intake opening has corrosion and closes up?

Yes that. Thanks

[1998233]

The challenge is on my 1997 233 you cannot see where the sea water pump intake hose connects to the transom, mostly because the power steering rack is on top it. I have heard it is really hard to get clevis pin out of steering arm.


https://www.youtube.com/watch?v=Mn6L8Fy ... A&index=82

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My question to the board is why or how would this static durable hose get pinched or bent at the transom when one cannot even lay a finger on it because it is so surrounded by other stuff?

[AsLan7]

The challenge is on my 1997 233 you cannot see where the sea water pump intake hose connects to the transom, mostly because the power steering rack is on top it. I have heard it is really hard to get clevis pin out of steering arm.


https://www.youtube.com/watch?v=Mn6L8Fy ... A&index=82

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My question to the board is why or how would this static durable hose get pinched or bent at the transom when one cannot even lay a finger on it because it is so surrounded by other stuff?

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It is quite difficult to access without pulling the engine but it can be done. Ironically we had a similar challenge and ended up pulling our engine anyways due to another issue (transom steering bracket snapped ) and fixed the intake properly. The aluminum actually corroded around the bolt thread of the intake housing which kept the housing from being tightly sealed around the intake hose causing air to be sucked in. That plastic piece may or may not have been collapsing as per that vid. There’s also a special tool required to insert and extract that plastic piece mentioned in the vid.

I documented the issue here.

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