7.4L Overheating

[CayugaCobalt]

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?

How do I confirm the thermostat is or is not working right other than removing and putting in pot of boiling water?

 

[Bondo]

Ayuh,..... I suspect the raw water pump, or the seawater pickup line, as if the t-stat was stuck, the exhaust rubber wouldn't have burnt up,.....

 

[alldodge]

Might very well be the new impeller. Installed a new one on mine this year and didn't make it to my slip. The impeller was extra hard to install was the only difference, but it came apart in pieces

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

Remove the hose going to the thermostat housing from the pump. Point it toward the bilge and start the motor

 

[johnkom]

When you reinstalled the lower unit to the upper and misaligned the water tube, that would make everything overheat pretty quickly. Don't ask me how I know.

JK

 

[Scott Danforth]

could be bravoitis

the brown rubber bits are now toast....... literally. you need new exhaust rubber bits including the flappers.

rubber bits are good for 250 degrees F max. exhaust temperatures without water are 1100-1400 degrees. the rubber bits never stood a chance.

 

[CayugaCobalt]

When you reinstalled the lower unit to the upper and misaligned the water tube, that would make everything overheat pretty quickly. Don't ask me how I know.

JK

I did not seperate my upper and lower units. But thanks for your input.

 

[CayugaCobalt]

could be bravoitis

the brown rubber bits are now toast....... literally. you need new exhaust rubber bits including the flappers.

rubber bits are good for 250 degrees F max. exhaust temperatures without water are 1100-1400 degrees. the rubber bits never stood a chance.

 

[CayugaCobalt]

so you are saying i need #5 and #7 and #8?

 

[Scott Danforth]

1, 5, 7, 8

 

[CayugaCobalt]

1, 5, 7, 8

Thanks, Scott. OEM part prices are silly high. For 1 and 5 you think aftermarket is ok?

 

[CayugaCobalt]

Might very well be the new impeller. Installed a new one on mine this year and didn't make it to my slip. The impeller was extra hard to install was the only difference, but it came apart in pieces



Remove the hose going to the thermostat housing from the pump. Point it toward the bilge and start the motor

The sea water pump aint pumping. No water reaching thermostat. No water coming out of water pump on the block. And not even any water coming out of the sea water pump outlet. I am presuming 20 seconds is an adequate test time?
Can you tell me a little more about your impeller story. I presume it was installed expertly and was OEM part?

 

[CayugaCobalt]

1, 5, 7, 8

looking like Bravoitis was the correct call. Sea water pump is fine except it aint pumping any water.

 

[alldodge]

The sea water pump aint pumping. No water reaching thermostat. No water coming out of water pump on the block. And not even any water coming out of the sea water pump outlet. I am presuming 20 seconds is an adequate test time?
Can you tell me a little more about your impeller story. I presume it was installed expertly and was OEM part?

Mine was a Merc OEM impeller, might have been 2 years old. Only thing different I noticed was it was extra hard to get the impeller in the housing. Use Glycerin and as before, it didn't make it to my slip before it over heated.

Had another on the shelf, replaced at the dock and this one went in easier. Somehow even a Merc went bad. Could be it was real old stock, I didn't notice at the time. Live and learn

 

[CayugaCobalt]

I see you told another boater with an overheating 454 that if you are in freshwater, like I am, it is very unlikely you have Bravoitis as Mr Danforth suggested. https://forums.iboats.com/threads/any-other-ways-to-solve-bravoitis.742355/

I also read where Mr Danforth mentioned any small air leak on intake side will diminish flow/suction. What if the ring gasket just isnt sealing the sea water pump housing, would this explain it?

 

[alldodge]

What if the ring gasket just isnt sealing the sea water pump housing, would this explain it?

That would cause some issues but if it did there would most likely be a leak.

Look at the hose under the bell housing and gimbal ring. It can twist sometimes when it gets old and will cut off the flow

Check the intake hose to make sure its on top of the raw water pump. Comes in on the top and to the motor on the bottom

 

[CayugaCobalt]

Definitely did not have hoses backwards on sea pump. Checked that. However the intake hose does look like an old dry salami and not like black rubber.

You can see how impeller was mixed up and off center. Was definitely rubbing the wear plate off center. I have flipped the wear plate over now to use the other side. Feels to me like the impeller doesnt reach the bottom of the housing and is setting up and out as far as O ring. Additionally in bottom of housing there is black ring that protrudes.

IMG 4009 Video shows no water reaching thermostat.

Not easy finding the transom end of that intake hose. Tried 5 times with phone camera.

I did muck about with my bilge pump last month and had to force it out from under the motor from the starboard side and then RAM it back under on same drivers starboard side. Maybe pump crushed the hose?

 

[CayugaCobalt]

That would cause some issues but if it did there would most likely be a leak.

Look at the hose under the bell housing and gimbal ring. It can twist sometimes when it gets old and will cut off the flow

Check the intake hose to make sure its on top of the raw water pump. Comes in on the top and to the motor on the bottom

There was no leak I saw of.
Is the hose under the bell housing and gimbal the intake hose?

 

[alldodge]

The ring in the bottom of the housing is wear. The housing should not have the ring, need new housing. I started replacing the entire pump every two season. $100 and done

 

[CayugaCobalt]

The ring in the bottom of the housing is wear. The housing should not have the ring, need new housing. I started replacing the entire pump every two season. $100 and done

entire new pump kit did not help. by removing the c shaped hose on the water pump, is this a valid way to test sea water pump? how long should it take for water to get picked up and pumped out these holes?

 

[alldodge]

Removing the hose will work, I would have removed the hose coming from the pump to the thermostat housing.

Don't know your serial number so the pic below is generic. Your motor should have a power steering and oil coolers. They are both inline with the hose coming from the raw water pump. Remove the hoses and back flush everything. Look closely at the oil cooler because they can get clogged